Experimentarium

Arbejdsgruppen arbejder p.t. med planer om et museum eller om muligt et ”Hands-on Eksperimentarium” og evt. et virtuelt eksperimentarium hvor eksempler på de instrumenter Martin Knudsen udviklede til dybhavsforskning, medico-fysiske forsøg samt andre fysiske forsøg og opstillinger kan komme til deres ret og afprøves af publikum. Det kan så bevares for eftertiden udover at være til glæde og læring for interesserede.
Netop i disse år er mange værdifulde, og absolut bevaringsværdige, samlinger fra Danmarks Guldalder for Havundersøgelser og oceanografi ved at blive herreløse.
På grund af den vanskelige økonomiske situation for Danmarks eksisterende museer og samlinger har disse svært ved at acceptere gaver og donationer i denne kategori p.g.a. omkostninger til opbevaring, registrering og udstillinger.
Det at vort håb at vi i arbejdsgruppen kan skaffe egnede lokaler til foreløbig opbevaring med henblik på senere offentlig udstilling.

Personer med arkivalier og samlinger vedrørende Havundersøgelser og Oceanografi, som kunne være interesseret i samarbejde om opbevaring og udstilling, bedes rette henvendelse til vor konsulent på dette område:
Lektor. Em Lic. et dr. scient. i Fysisk Oceanografi Niels Kristian Højerslev på: nkh@gfy.ku.dk

Personer med arkivalier og samlinger vedrørende medico-fysik, gassers kinetik, elektromagnetisme samt strømningsfysik, som måtte være interesserede, bedes rette henvendelse til Bjarne Fredberg Knudsen på: bfk@empas.dk

Personer med arkivalier og samlinger vedrørende Martin Knudsens barndom og opvækst, lokalhistorisk perspektiv, som måtte være interesseret i de ovenfor skitserede initiativer bedes rette henvendelse til Carl Pedersen på: carlgmpederen@gmail.com

Henvendelser vedrørende denne hjemmeside bedes rettet til webmaster på:

martinknudsen71@gmail.com

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Foreløbigt museum

1: Forsøg og opstillinger lavet af Professor Martin Knudsen

2: Arkivalier med tilknytning til Professor Martin Knudsen

3: Artikler (og links) til relevante emner vedr. Martin Knudsens arbejder og forskning

Hans Jørgen Nielsen, Konservator v. Københavns Universitet. Liv og levned.
Professor Martin Knudsens gode ven og samarbejdspartner,som fremstillede de instrumenter Martin Knudsen brugte i sin forskning vedr. oceanografi. m.m.
Konservator Hans Jørgen Nielsen (BLW) 120315-30
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1: Forsøg og opstillinger lavet af Professor Martin Knudsen

Martin Knudsen´s erfaringer med cigarrygning – fra Røgringe til kuglelyn:
(under redigering illustrationer mangler)
(For hele filen med illustrationer, tryk på linket herunder)
Martin Knudsen eksperimenter røgringe til perlyn 110830-3

Vi har en centrifuge. Den centrifugerer vasketøj, så vandet i det våde tøj slynges ud, falder ned i bunden og pumpes ud. Som mange centrifuger består den af en skål, der drejer om en akse. Skålens væg er perforeret, rustfrit stål, stærk nok til at holde på vasketøjet. Og gennemtrængelig for vand der skal væk. God nok til sit formål. Men plasma kan den ikke centrifugere. Plasma kan vanskeligt spærres inde af faststof. Enten vil det faste stof afkæle plasmaen utilladeligt, eller den mange tusind grader varme plasma vil destruere det faste stof. Til at ”holde” på en klum, plasma må man anvende en ”magnetisk flaske”, et magnet felt, som confin´er plasmaen. Det skabes i de fleste fysiske apparater af store elektromagneter, af og til også under anvendelse af supraledning, for at få dem kraftige nok. At bringe store elektromagneter til at rotere som en centrifuge lyder mildt sagt vanskeligt.
Det ser ud til der skal andre metoder til: En centrifuge uden skål med faste vægge har man f.eks. i en røgring. Man kan fylde sin mund med røg (eller man kan bede en ryger om at udføre forsøget for en). Munden åbnes til et stort O og med tungen som stempel kan man foretage en stødvis udblæsning af røgen. Med nogen øvelse kan nogle rygere derved blæse en røgring (Åge Knudsen var eminent til det!). Store flotte røgringe har jeg også set komme ud af stenfiskerens og fiskerbådes udblæsningsrør. De allerflotteste og bedst kontrollerede røgringe jeg bhar været præsenteret for var de fysiske forsøg vi lavede som medicinske fysikforsøg. Det var forsøg designet af professor Martin Knudsen tilbage i 1920´erne.

Jeg husker det således: Se fig.1. På katederet var opstillet to store næsten kubiske kasser med henved en meters mellemrum. I hver kasse havde den side, der vender mod den anden kasse, et hul med en diameter på 5cm. Den modstående side i hver kasse bestod af en gummi membran. Hver kasse havde desuden en lem. Gennem denne kunne der sættes en skål med en væske som fyldte kasserne med røg (flydende kulsyre, kvælstof, eller ammoniak + saltsyre). Når man slog på gummimembranerne, skød der en tyk flot røgring ud af kassens hul. Røgringene havde fart på – det var som om de ”svømmede” afsted gennem klasseværelset, for så efter få sekunder at gå i stå og opløses i en lille røgsky. Ringen hed ”vortex”, fik vi at vide. Røgringen gik i stå ved friktionen med den omgivende næsten stillestående luft i klasseværelset.

Røgringe fremstillet af ammoniak og saltsyre
Men så blev der slået på begge kasser samtidigt. Og efter et par forsøg, hvor ringene passerede forbi hinanden, lykkedes det at få de to røgringe til at ramme hinanden centralt trods den store afstand mellem kasserne. Så ”klistrede” de to røgringe sammen til en ”dobbelt-vortex” og denne var mange gange mere stabil end de enkelte røgringe. Den dobbelte røg-vortex svævede langsomt rundt i klasserummet måske drevet af trækken fra radiatorerne?
Dobbelte røg-vortex´ernes ”levetid” var væsentlig længere end enkelt-vortex´erne måske 10-15 sekunder længere.

Hvis man som det ses af fig.2 lægger et snit gennem en dobbelt vortex-røgring, og alene betragter den bageste del, så ses det, at pustet fra kassens hul at pustet fra kassen går gennem røgringens midte og i ringens yderside bevæger røgen sig tilbage. I et snit gennem ringen vil røgen dermed rotere. Derved ligner røgringen et svinghjul. Man kan altså sige at Martin Knudsen´s enkelte og dobbelte vortex´er faktisk er centrifuger med cirkulære rotationsakser. Bevægelsesenergien som overføres til ”røgsvinghjulet” stammer udelukkende fra anslaget på kasse væggene. Hvis nu røgen i kasserne blev erstattet af plasma? Fik man så en plasma-centrifuge? Hov nej, for kasserne kan ikke indeslutte plasma. Plasma kan confines i en magnetisk flaske.
Jamen, sådan en har man jo i en lynbane, sålænge lynstrømmen varer! Plasma indeni. Elektrisk strøm på langs igennem lynbanen. Denne strøm er ledsaget af et magnetfelt, som confiner lynbanen. Det ser virkelig ud som om der er lagt an til dannelse af en plasmacentrifuge. Men der sker jo normalt ikke noget! Den elektriske strøm dør ud. Confinement´en – den magnetiske flaske – forsvinder med lynstrømmen. Røret er væk! Der blev ikke slået på noget der ligner membranerne i røg-kasse modellen. Ofte ser man dog en serie af nye lyngennemslag i den samme bane. Rester af joniseret luft bevirker at nye udladninger er tilbøjelig til at følge samme bane. Strømmen varer hver gang kun få millisekunder; men er tilgengæld på flere tusind ampere. Som regel varer det 10-50 millisekunder før det nye gennemslag finder sted gennem samme joniseringsbane. 5-6 lyn passerer ofte gennem den samme lynbane; men med pauser imellem. Disse tal kendes fra fotografiske optagelser med roterende spejl.
Men uhyre sjældent må det kunne ske, at et nyt lyngennemslag kommer så tæt efter det forrige, at strømmen fra det første lyn stadig er ”on” når det næste gennemslag kommer. Eller med andre ord, at et nyt lyn rammer en eksisterende lynbane. Og så er der lagt op til at der kan sker noget spændende: Det nye lyngennemslag virker som slaget på membranen på Martin Knudsen´s røgkasser, for et nyt lyngennemslag vil særdeles pluseligt øge temperatur og confinement – og dermed trykket – enormt. Men hvor er hullerne fra Martin Knudsen´s røgrings-kasser? Ja, se nu er et lyn altså ikke spor retlinet. Det slår nogle gevaldige knæk. Og i ydersiden ved et knæk må lynbanens confinement have en svækkelse. Svækkelse og et pludseligt opstået forøget tryk må uvægerligt føre til en utæthed i den magnetiske flaske. Når det sker lige i det øjeblik hvor trykket i confinement-røret er vokset, så opstår der en stød-agtig bevægelse af hele plasmaen fra begge sider hen mod utætheden. Se fig.3.

Det er præcist den ideelle situation for skabelse af en dobbelt-vortex. Vel nok endnu bedre end Martin Knudsen´s eksperiment hvor der 1) skulle bankes rimeligt samtidigt på de to kassebagvægge, og 2) skulle sigtes godt på grund af den store afstand mellem kassernes huller, som var nødvendig af hensyn til de studerendes mulighed for at se at de to vandrende enkelt-røgringe mødtes og kobledes sammen til en dobbelt-vortex. Ved ”lyn i lyn”er samtidigheden tilstede af sig selv og tillige ligger confinement´ernes ”rørmundinger” i hinandens forlængelser i lynbanens knæk og endda tæt overfor hinanden. Fig.3 viser skitsemæssigt et øjebliksbillede af det meget korte tidsrum, hvor jævnstrømmen fra det første gennemslag endnu ikke er døet ud, og hvor det andet lungennemslag lige akkurat skal komme. Magnetfeltet, som confiner plasma strengen er skematisk vist som et ugennemsigtigt rør, som har et af lynbanens mange knæk midt i billedet. Lidt for simplet er svækkelsen vist som et knæk på røret. For simplet, dels fordi magnetfeltet jo er usynlgt, dels fordi ”svækkelsen”af magnetfeltet jo ikke har karakter af et ”brud” på røret; men – nå ja – netop blot er en svækkelse. At svækkelsen egentlig alene findes i knækkets yderside har kun sekundær betydning i sammenligning med det voldsomme stød, som sætter lyn-banens plasmaindhold i ét stort stød, i bevægelse fra begge sider, hen mod utætheden.

Et øjeblik senere er den dobbelte vortex dannet. Dette er vist skamatisk i fig.4. En meget stor del af det andet gennemslags elektriske energiindhold vil være medgået til at skabe rotationen i den dobbelte vortex, så svinghjulet har fået masser af energi. Det betyder at plasmaen roterer hurtigt omkring de to cirkulerende vortex´ers rotationsakser.
Jamen, så er der altså dannet en plasma-centrifuge!!
Man må simpelthen forvente at under de givne betingelser, (et første gennemslag og, inden dettes lyn er ophørt, et nyt lyn, der rammer det gamle), så må der kunne dannes en dobbel plasmavortex, som er en plasmacentrifuge. Eller rettere: På lynbanen må man forvente at et antal sådanne vortex´er på steder, hvor lynbanen har knæk. Og på afstand må de se ud som kugler. Nå ja, ét er, at man må forvente at et sådant fænomen skulle kunne finde sted, men ér det observeret?? —ja det er det!! Endda så mange gange at de har fået et navn: Det kaldes et PERLELYN

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2: Arkivalier med tilknytning til Professor Martin Knudsen
(klik på link herunder)
Brev fra MK til Niels Bohr af 13-03-1912
Til Niels Bohr fra MK (Nobelprisen i 1922)
Fru E Knudsen til Niels Bohr (Mk død i 1949)
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3: Artikler (og links) til relevante emner vedr. Martin Knudsens arbejder og forskning
Artikkrel i PhysRevLett. i Sept.2011 med henvisning til Martin Knudsen
Physics 2011 med henv. til Martin Knudsen
Kronik i FS
Fysikeren fra Hasmark – Kronik FyesnStifttidende 110921
Københavns Universitets jubilæumsskrift fra 1979 om Martin Knudsen

Kinetisk Teori (under redigering illustrationer mangler)
(For hele filen med illustrationer, tryk på linket herunder)
Kinetisk Teori 120104-2
kinetisk teori, fysisk teori for gassers og andre fortyndede partikelsystemers egenskaber. Den kinetiske teori blev grundlagt af R. Clausius, J.C. Maxwell og L. Boltzmann i sidste halvdel af 1800-t. De mest afgørende bidrag fra 1872 og 1896 skyldes Boltzmann, hvis metoder til en kvantitativ beskrivelse af gassers varmeledningsevne og viskositet har vist sig anvendelige i mange andre sammenhænge. Den kinetiske teori blev udviklet med henblik på at forstå fortyndede klassiske gassers opførsel, men den er i løbet af 1900-t. blevet anvendt på metaller, halvledere, superledere, plasmaer og andre partikelsystemer, der i en eller anden forstand kan betragtes som fortyndede.
I en fortyndet gas er afstanden mellem molekylerne langt større end molekylernes udstrækning. Det er derfor muligt at betragte partiklerne som frit bevægelige i tidsrummene mellem deres indbyrdes sammenstød. Den kinetiske teori giver en statistisk beskrivelse af partiklernes fordeling i det seks-dimensionale faserum, der udgøres af en partikels stedvektor r og impulsvektor p. Den statistiske fordelingsfunktion f(r,p,t), der i almindelighed afhænger af tiden t, er et mål for antallet af partikler i et lille område omkring punktet (r,p) i det seksdimensionale faserum.
Den kinetiske ligning, der også betegnes Boltzmann-ligningen, beskriver, hvorledes den statistiske fordeling ændres dels på grund af partiklernes bevægelse i ydre felter, dels på grund af deres indbyrdes sammenstød. Ved at løse den kinetiske ligning kan man finde fordelingsfunktionen for fx metalelektroner, der accelereres af et ydre elektrisk felt, mens de bremses af stød mod urenheder eller fononer. Herved kan størrelsen af metallets elektriske modstand beregnes, idet den elektriske strømtæthed kan findes ud fra kendskabet til fordelingsfunktionen.
I klassiske gasser giver den kinetiske teori en præcis beskrivelse af fx viskositetens størrelse og temperaturafhængighed. For simple partikelsystemer som ædelgasser er forskellen mellem eksperimentelt målte og teoretisk beregnede værdier af viskositeten meget lille, normalt under 1%.
Selvom kvantemekanikken begrænser muligheden for at angive nøjagtige værdier af en partikels sted og impuls (jf. Heisenbergs ubestemthedsrelation), kan den kinetiske beskrivelse også anvendes på kvantesystemer, forudsat at de ydre felter varierer tilstrækkelig langsomt i rum og tid. Det er også muligt at tage hensyn til, at partiklernes vekselvirkning giver anledning til et middelfelt, der påvirker den enkelte partikels bevægelse. Herved bliver den kinetiske teori også anvendelig for fysiske systemer som superledere og kvantevæsker, hvor partiklernes indbyrdes vekselvirkning spiller en afgørende rolle.
atomare kollisioner, sammenstød mellem et atom eller en ion og elektroner, fotoner, atomer eller ioner; herved foregår der fysiske og i visse tilfælde kemiske processer, hvis beskrivelse og forståelse kan sammenfattes i studiet af atomare kollisioner. Meget nært relateret hertil — og ofte også omfattet af samme betegnelse — er de stødprocesser, hvori molekyler eller molekylioner indgår.
I store dele af verdensrummet, hvor der findes frie atomer, ioner eller molekyler som fx i Jordens, Solens samt de øvrige planeters og stjerners atmosfærer eller i det interstellare rum, er atomare stødprocesser meget betydningsfulde. Fx bestemmes formen på solspektret i det synlige område, et emne af fundamental betydning for alt liv på Jorden, af fotoners kollisioner med negative brintioner på Solens overflade. De astrofysiske og atmosfærefysiske stødprocesser kan i nogle tilfælde udforskes fra Jorden, nemlig når processen er ledsaget af lysudsendelse (fx nordlys) eller anden elektromagnetisk stråling, der kan trænge igennem Jordens atmosfære, eller de kan studeres ved hjælp af udstyr, der opsendes med balloner, raketter eller rumfartøjer.
På Jorden er atomare kollisioner betydningsfulde inden for mange grene af naturvidenskab og teknologi. Som eksempler kan nævnes stødprocesser i gasser, der udnyttes til frembringelse af elektriske lyskilder og gaslasere, eller stødprocesser på overflader og i faste stoffer, hvorved det er muligt at opnå informationer om de geometriske strukturer eller om den kemiske sammensætning af disse materialer. Ved hjælp af acceleratorer, der frembringer energirige elektroner, fotoner eller ioner, er det også muligt via atomare kollisioner at modificere de mekaniske, kemiske eller elektroniske egenskaber hos faste stoffer, hvilket har bidraget til udvikling af nye eller forbedrede materialer. Atomare kollisioner, der finder sted i levende væv, udnyttes fx inden for strålebehandling og til at frembringe mutationer hos planter. Kollisionsprocesser mellem ioner indtager en central rolle inden for fusionsforskningen, som tilstræber en energiproduktion gennem sammensmeltning af atomare ioner.
Atomare kollisioner kan inddeles i elastiske kollisioner, for hvilke det gælder, at den totale kinetiske energi af de kolliderende atomer er den samme før og efter kollisionen, samt uelastiske kollisioner, i hvilke en del af den kinetiske energi anvendes til at excitere eller ionisere de kolliderende atomer.
Elastiske kollisioner
Tanken om at udlede luftarternes egenskaber fra atomernes eller molekylernes bevægelse blev endeligt udformet i den kinetiske gasteori i midten af 1800-t. Atomer og molekyler i en luftart bevæger sig ved stuetemperatur med hastigheder svarende til en gennemsnitlig kinetisk energi på under 1/50 af, hvad der kræves for at excitere et atom fra dets grundtilstand. De elastiske kollisioner, som luftartens atomer tager del i, resulterer i en ændring af bevægelsesretningerne samt en overførsel af energi mellem de kolliderende atomer. Sandsynligheden for, at en given stødproces vil finde sted, udtrykkes ved et reaktionstværsnit, der opgives som et areal. Sådanne tværsnit bestemmer en lang række egenskaber hos luftarterne såsom middelvejlængde mellem to kollisioner, diffusion, gnidning og varmeledningsevne.
Uelastiske kollisioner
Når energien af de kolliderende atomer øges, aftager den relative sandsynlighed for elastiske kollisioner, og tværsnittet for uelastiske kollisioner, i hvilke én eller begge de kolliderende partnere bliver exciteret eller ioniseret, dominerer. Lige siden E. Rutherford i begyndelsen af 1900-t. anvendte kollisioner mellem atomare partikler til at udforske atomer (se atom), har uelastiske kollisioner indtaget en central rolle i udredningen af atomets og atomkernens struktur. Ved stød mellem atomer og elektroner efterviste J. Franck og G. Hertz således kvantiseringen af atomets energiniveauer, som forudsagt i Niels Bohrs atomteori. Excitationen af atomer som følge af uelastiske stødprocesser med elektroner er den dominerende proces for lysudladning i gasser, der nyttiggøres i fx elektriske lamper. Excitation er også den dominerende mekanisme for energiafsættelse for ladede partikler, der passerer igennem stof, en mekanisme, der udnyttes til detektion af ladede partikler. En meget betydningsfuld gruppe af uelastiske atomare kollisioner udgøres af de reaktive kollisioner, som danner grundlaget for væsentlige dele af kemien, og hvorved projektilatomet og objektatomet efter stødet udgør et molekyle. Reaktive kollisioner sker fx under forbrændingsprocesser.

Tryk i luftarter.
Hvordan forklares luftens tryk. Vi kan få en ide ved at se på en luftart fyldt i en kasse (Fig. 1). Luftarten består af molekyler og det er deres stød med væggene som giver anledning til trykket. Det er mængden af stød der afgør hvor højt trykket p er. I kemien benyttes begrebet antal “mol” n. Der gælder følgende formel, hvor m er massen af luftarten og M er molmassen:
TRY(4.1)

Til måling af temperaturen benyttes den absolutte temperatur T der måles i kelvin (K). I forhold til temperaturen t i grader Celsius.
TRY(4.2)

Fig. 1. En beholder fyldt med molekyler. Molekylerne bevæger sig i alle mulige retninger. Når de rammer en af væggene vil de blive kaste tilbage fra væggen. Jo flere molekyler der rammer væggene, jo højere er trykket. Er temperaturen høj vil molekylerne bevæge sig hurtigere og derved øges chancen for de rammer væggene. Hvis temperaturen sænkes til det absolutte nulpunkt – 273,15 0C vil molekylerne efterhånden ligge stille og derfor vil trykket falde til nul.

Udledning Idealgasloven.
Trykket afhænger af følgende størrelser:
• Kassens størrelse eller volumen V.
• Den absolutte temperatur T i kassen.
• Antal mol n i kassen.
De ovennævnte resultater kan samles i en formel der kaldes for idealgasloven og som gælder for næsten alle gasser (luftarter):

TRY(4.3)

Her er R en konstant, kaldet gaskonstanten der gælder for alle de ideale gasser.
TRY(4.4)

Bemærk at V skal måles i kubikmeter og p i Pascal. Enheden for R: er Joule per mol per Kelvin. En Joule er et mål for energi og er det samme som en Newton-meter, således at enhederne stemmer.

At idealgasloven er rigtig kan undersøges med en række forsøg. Hvis vi undersøger trykket i en kanyle finder vi følgende resultat, som kaldes Boyle-Mariottes lov. Her er k en konstant altså et tal.
En sådan proces hvor temperaturen er konstant kaldes en isotermisk proces.
TRY(4.5)

Vi kan også undersøge hvordan p afhænger af T, hvis rumfanget er konstant. Det fører til følgende lov:
TRY(4.6)

også kendt som Charles lov.
Lad os benytte disse to love til at udlede idealgasloven. Betragt figur 3. Til start er trykket p1, rumfanget V1 og temperaturen T1. Stemplet flyttes nu ud til det nye rumfang V2 men temperaturen er den samme. Trykket er faldet til p. Vi har da fra Boyle-Mariottes lov:

TRY(4.6a)
som omskrives til:

TRY(4.6b)
Stemplet holdes nu fast så rumfanget er V2 men temperaturen ændres til T2. Trykket er steget til p2. Vi har da fra Charles lov:

TRY(4.6c)
som omskrives til:

TRY(4.6d)
Ved sammenligning af TRY(4.6b) og TRY(4.6d) fås:

TRY(4.6e)
som giver idealgasloven:

TRY(4.6f)

Fig. 3. Udledning af idealgasloven sker ved en totrinsproces. Først flyttes stemplet ud under konstant temperatur. Under denne proces gælder Boyle-Mariottes lov. I den anden proces ændres temperaturen medens rumfanget er konstant så Charles lov gælder.

Varme og energi.
Har vi en gas indesluttet i en beholder kan vi øge den indre energi også kaldet den termiske energi E eller U enten ved:
• at opvarme gassen ved at tilføre varme Q
eller ved:
• at udføre et stykke arbejde A eller W på gassen, ved at trykke gassen sammen.
Ændringen i den indre energi er givet ved:
TRY(4.7)
Det kaldes for varmeteoriens første hovedsætning. For en ideal (monatomig, ædelgas) gas gælder at ændringen i den indre energi kun afhænger at ændringen i temperaturen:
TRY(4.8)
Det kan udledes ved at se på kinetisk molekylteori. Her er CV den molære varmefylde ved konstant rumfang, CP er den molære varmefylde ved konstant tryk. Varmefylden er det vi kender fra opvarmning af væsker, medens CP ofte benyttes i kemien. Hvis gassen er toatomig (oxygen, nitrogen) bliver CV = 5/2R og CP = 7/2R.
Det udførte arbejde på en gas er givet ved (se figur 3):
TRY(4.9)

Fig. 3. Når et stempel i en cykelpumpe bliver trykket ind, udføres der et stykke arbejde, som afhænger af kraften og dermed af trykket.

Isotermisk arbejde.
Lad os se på det udførte arbejde under konstant temperatur kaldet en isotermisk proces. Vi benytter idealgasloven og finder:
ved integration (se figur 4) mellem grænserne V1 og V2:
TRY(4.10)
Da gassen udvider sig er V2 er større end V1, så gassen har udført et positivt arbejde på os, medens vi har udført et negativt arbejde på gassen. Trykker vi derimod gassen sammen vil vi udføre et positivt stykke arbejde.
Projekt 1. Gennemgå trinnene i den sidste ligning.

Fig. 4. Arbejdet på en gas er givet ved arealet under grafen. Hvis gassen presses sammen er det os der udfører et positivt arbejde på gassen og hvis gassen udvider sig er det gassen der udfører arbejde på os.

Adiabatisk proces.
Hvis systemet ikke udveksler varme med omgivelserne vil Q være lig nul. Det er hvad der sker op gennem atmosfæren. For sådan en adiabatisk proces gælder følgende sammenhæng:
TRY(4.11)
hvor k er en konstant. Ligningen minder stærkt om Boyle-Mariottes lov.
Projekt 2. Vis ved at benytte idealgasloven og TRY(4.11) at der også gælder:
TRY(4.12)
hvor k er den samme konstant som før.
Fra TRY(4.7) finder vi:
TRY(4.13)
og fra TRY(4.8) følger:
TRY(4.14)
For en adiabatisk proces er Q = 0. Det følger at der må gælde:
TRY(4.15)
og dermed ved division med dT at:
TRY(4.16)
Projekt 3. Vis ved at benytte idealgasloven og TRY(4.12) at TRY(4.16) er opfyldt.
Projekt 4. Udregn som under TRY(4.10) arbejdet ved en adiabatisk proces.
Projekt 5.
Udnyt i det følgende at:

TRY(4.17)
samt at der altid gælder:

TRY(4.18)
til at vise at arbejdet kan skrives på den simple måde:

TRY(4.19)

CP og CV.
Lad os se på en proces hvor luften opvarmes ved konstant volumen. I følge TRY(4.14) gælder der:
TRY(4.20)
Det svarer til den sædvanlige formel for opvarmning af et fast eller flydende stof. Da CV er den molære varmefylde kan man også benytte det sædvanlige udtryk hvor n erstattes med massen m og CV med varmefylden c.
Hvis vi opvarmer luften ved konstant tryk har vi per definition:
TRY(4.21)
Da p er konstant følger fra TRY(4.14) at:
TRY(4.22)
Ved at benytte idealgasloven TRY(4.3) får vi:
TRY(4.23)
og dermed:
TRY(4.24)
Ved sammenligning af TRY(4.21) og TRY(4.24) følger resultatet i TRY(4.18).
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Medico-Fysik (Artiklen er under redigering illustrationer mangler)
(For hele filen med illustrationer, tryk på linket herunder)
Medico-Fysik Videreudvikling af Martin Knudsens forsøg 110813-1

Medico udvikling omfatter en bred vifte af aktiviteter, og er alternativt kaldet bioteknologi og Biomedical Engineering. Det er et tværfagligt emne der integrerer faglige ingeniør kundskaber med en grundlæggende medicinsk viden om den menneskelige krop og en forståelse af, hvordan det fungerer med raske, syge eller tilskadekomne.
Mange af de fremskridt på dette område synes almindelige så som – hofte udskiftninger, pacemakere, medico-billeddannelse, livsnødvendige systemer og medicinske lasere er blot et par eksempler på resultaterne af omfattende industriel forskning og udvikling, som ofte er groet ud af offentlig forskning. En pionér i Danmark for medico-fysiske udviklinger blev gjort af professor Martin Knudsen, som var leder af Medico-fysisk samling ved Københavns Universitet.
Medico ingeniører opfylder et behov for sundhedssektoren – som er verdens største industrielle sektor, som har en omsætning, der nærmer sig 1000 milliarder kroner om året – og er i øjeblikket ved at udvide med en sats på 7% om året. Mulighederne for medico ingeniører er enorme, og det er et af de få områder inden for teknik, der ventes at fortsætte med at vokse i mange år.
Storbritannien er en af verdens førende inden medico forskning og fremstilling og tilbyder mange universitetsstudierne og kurser. Den brede vifte af aktiviteter der omfatter emnet betyder, at fokus for medicinalteknik kan være meget forskellige – der er flere emner at vælge imellem indenfor medico end i andre mere traditionelle ingeniørfag. For eksempel, hvor de fleste medicinske ingeniører i dag har et mekanisk eller elektronisk grunduddannelse, er der andre der kan være fokuseret mere på materialelære, fysik eller biologi.
Biomedical kontra Mediko
Mediko udvikling Professor Martin Knudsen var i første halvdel af 1900-tallet foregangsmand for konstruktion og opstillinger af medico-fysiske apparaturer i Danmark. I dag har medico udviklingen centrale moduler i maskinteknik og basal medicin, sammen med specialiserede moduler i Biomekanik, biofluids og biomaterialer, implantat design og kunstige organer, rehabilitering engineering, computer-og robotteknologi bistået kirurgi, vævsmanipulering, medicinske apparater og udstyr, fysiologiske målinger, medicinsk billeddannelse og diagnosticeringsteknikker, og lovgivningsmæssige spørgsmål og medicinsk etik.
Direkte forbindelser med de lokale hospitaler og helst en medico uddannelse er afgørende, hvis man skal have klinisk erfaring.
I lighed med de fleste ingeniørvidenskabelige fag, team-arbejde, præsentation og inter-personlige færdigheder er meget vigtige for medico ingeniører da de ofte vil være den person, der bygger bro over kløften mellem klinikere, patienter, salg og markedsføring, og fremstillingsaktiviteter. Medicinal ingeniører er imidlertid enestående i deres systemer og integrerende tilgang til problemløsning, deres evne til at føre resultaterne af grundforskningen i den kommercielle og kliniske indstilling og deres evne til at fungere i et tværfagligt miljø.

Medicinsk udstyr er designet til at støtte i diagnosticering, overvågning eller behandling af medicinske tilstande. Disse enheder er normalt konstrueret med strenge sikkerhedsstandarder.
De vigtigste emner: implantat, kunstige lemmer, korrigerende linser, cochlear implantater, dental implantater, proteser (okulær, facial)

Grundlæggende medicinske apparater
• Diagnostisk udstyr omfatter medicinsk billeddannelse maskiner, der anvendes til at understøtte diagnosen. Eksempler herpå er ultralyd og MR-maskiner, PET og CT-scannere og røntgenudstyr.
• Terapeutiske udstyr omfatter infusionspumper, medicinske lasere og LASIK kirurgisk udstyr.
• Livs opretholdende udstyr anvendes til at sikre patienters kropslige funktion. Disse omfatter medicinske ventilatorer, hjerte-, lunge-maskiner, ECMO, og dialyse maskiner.
• Kliniske computer programmer muliggør at medico-medicinsk personale kan måle patientens medicinske tilstand. Observatører kan måle patientens vitale tegn og andre parametre, herunder EKG, EEG, blodtryk, og opløste gasser i blodet.
• Klinisk-kemisk laboratorieudstyr som hel- eller halvautomatisk analyserer blod, urin og gener.
• Diagnostisk medicinsk udstyr, kan også bruges i hjemmet til visse formål, fx til kontrol og behandling af diabetes mellitus
Medicinske apparater er afgørende resultatgivende elementer i sundhedssektoren. Personalet uddannet til anvendelsen og serviceringen af avanceret udstyr kaldes ofte biomedicinsk udstyrs teknikker eller på engelsk Biomedical Equipment Technician forkortet som BMET . De er hovedsageligt beskæftiget ved hospitaler og refereres ofte til som medico ingeniører, der er ansvarlige for at sikre det medicinsk udstyrs funktionalitet.
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List of publications about ICES history, compiled by Jens Smed (former ICES Hydrographer).
The list is not complete, but forms a solid core for the building of a more comprehensive list, containing references to internationally published literature as well as literature published in member countries.
Record of Persons and Events
LIST OF PRESIDENTS 1902 – 2009
1902 – 1908 W. Herwig, Germany
1908 – 1912 W.E. Archer, UK
1912 – 1915 F. Rose, Germany
1915 – 1920 Otto Pettersson, Sweden
1920 – 1938 Henry G. Maurice, UK
1938 – 1948 Johan Hjort, Norway
1948 – 1952 K.A. Andersson, Sweden

LIST OF VICE–PRESIDENTS 1902 – 2011

1902–1913 O. Pettersson, Sweden
1908–1913 O. von Grimm, Russia
1908–1912 F. Rose, Germany
1913–1914 N. Knipowitch, Russia
1912–1920 H.G. Maurice, UK
1920–1938 J. Hjort, Norway
1920–1921 M J. Kerzoncuf, France
1921–1944 M T. Tissier, France
1927–1944 C. Heinrici, Germany
1933–1947 M. Knudsen, Denmark
1938–1946 A.T.A. Dobson, UK
1945–1948 K.A. Andersson, Sweden
1947–1954 G.J. Lienesch, Netherlands
1948–1951 A. Ramalho, Portugal
EXTRAORDINARY MEMBERS OF THE BUREAU

1902–1908 C.F. Drechsel, Denmark
1903–1908 D’Arcy Wentworth Thompson, UK
1903–1908 F. Nansen, Norway
1903–1908 O. von Grimm, Russia
1907 Th. Lewald, Germany
1908 W.E. Archer, UK
1908 F. Rose, Germany

GENERAL SECRETARIES 1902 – 2006
1945 – 1950 H. Blegvad, Denmark
1944 – 1945 E. Brønniche, Denmark (Acting Administrative Secretary)
1932 – 1944 M.W. Nellemose, Denmark
1927 – 1932 Schøning, Denmark (Administrative Secretary)
1908 – 1927 C.F. Drechsel, Denmark (Member of the Bureau)
1902 – 1908 P.P.C. Hoek, the Netherlands (Member of the Bureau)
LIST OF CHAIRMEN OF THE CONSULTATIVE COMMITTEE 1925 – 2008/ SCICOM 2009- 2010
1950 – 1952 G.M. Graham, UK
1946 – 1950 R.S. Clark, UK
1938 – 1946 E.S. Russell, UK
1925 – 1938 J. Hjort, Norway
Statuary meetings and Annually science conferences 1902-1948
Statutory Meetings and Annual Science Conferences 1902 – 2011
1902 22 July Copenhagen
1903 23 February Copenhagen
1904 25 February Hamburg
1905 21 July Copenhagen
1906 27 February Amsterdam
1907 13 June London
1908 17 July Copenhagen
1909 06 August Copenhagen
1910 22 September Copenhagen
1911 No formal meeting
1912 22 April Copenhagen
1912 18 September Copenhagen
1913 16 September Copenhagen
19181 23 May Copenhagen
1920 02 March London
1921 14 July Copenhagen
1922 14 September Copenhagen
1923 01 October Paris
1924 11 September Copenhagen
1925 01 September Copenhagen
1926 06 September Copenhagen
19272 23 May Copenhagen
19272 27 May Stockholm
1928 04 June Copenhagen
1929 08 April London
1930 26 May Copenhagen
1931 23 March Copenhagen
1932 20 June Copenhagen
1933 08 May Paris
1934 04 June Copenhagen
1935 27 May Copenhagen
1936 11 May Copenhagen
1937 05 July Copenhagen
1938 23 May Copenhagen
1939 10 May Berlin
1945 15 October Copenhagen
1946 12 August Stockholm
1947 20 October Copenhagen
1948 04 October Copenhagen
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Salinimetry – History of the salinity determination 120203-7

(under redigering. Illustrationer mangler)
(For hele filen med illustrationer, tryk på linket herunder)
Salinimetry – History of the salinity determination 120203-7

Chapter 1: Early Determination of Salinity: from Ancient Concepts to Challenger Results
Chapter 2: Introduction of the International Standard Seawater – by Martin Knudsen
Chapter 3: Implementation of the electrical conductivity of seawater –partly M.Knudsen
Chapter 4: Development of the Practical Salinity Scale
1. Early Determination of Salinity: from Ancient Concepts to Challenger Results
Empedocles

The saltiness of seawater has been recognized throughout recorded history. Theories about origin of the seawater and nature of saltiness of the sea have first been formulated by ancient philosophers. In the 6th century BC Greek scientists abandoned mythological interpretations of the universe in favor of explanation relying on natural causes. Famous pre-Socratic philosopher and poet Empedocles (490-430BC) is known as a founder of the cosmogony theory of the four classical elements. But he was also the first philosopher, who left such poetical definition of the seawater origin: “The Sea is the Sweat of the Earth ” (The Fragments, Book1, p.179) Another philosopher said that all the earth was at first surrounded with moisture, some of which later formed the sea in a process of drying which would ultimately end in the loss of the sea (attributed to Anaximander and Diogenes of Apollonia). One more philosopher simply attributed the saltiness to the earth that the water picked up as it came in contact with the earth as it ran over it, just as water strained through ashes is known to be salty. The sea itself was explained by the accumulation of the run-off (attributed to Metrodorus of Chios and Anaxagoras).

Aristotle

Aristotle (384-322BC) summarized Greek philosopher´s views by saying: “At first the Earth was surrounded by moisture. Then the sun began to dry it up, part of it evaporated, and is the cause of winds while the remainder formed the seas. So the seas are being dried up. Others say that the sea is a kind of sweat exuded by the earth when the sun heats it, and that this explains its saltiness, for all sweat is salt. Others say that the saltiness is due to the earth. Just as water strained through ashes becomes salt, so the sea owes its saltiness to the mixture of earth with similar properties.” Aristotle mentioned that salt water was heavier and more dens than fresh water, and salt water would seek a lower level. Aristotle was aware that the sea contained other than just salt and commented on both its salt and bitter taste. Aristotle apparently was the first person to have noticed and attempted to explain the bitter quality of sea water – a point which did not occur in the literature for at least two thousand years later. More specifically he was the first to mention something other than salt and water in seawater. The salt from the sea (prepared by evaporation) was weaker in saltiness and was generally not as white, and less lumpy than “normal” salt. He added: “Why is the sea salty and bitter? Is it because the juices in the sea are numerous? For saltiness and bitterness appear at the same time.” One of Aristotle’s experimental proofs that saltiness is due to the admixture of some substance was with the use of a completely closed wax vessel. This container was lowered into the sea and: “then the water that percolates through the wax sides of the vessel is sweet, the earthy stuff, the admixture of which makes the water salt, being separated of as it were by a filter.” Aristotle’s attempts to explain the saltiness of the sea were hardly altogether clear and the wax container experiment is just one simple example. Later confusion and misconceptions did arise concerning this subject area. From a compositional standpoint, Aristotle tried to answer the questions: why the sea water was salty, why water which is naturally fresh became salt, and what was the nature of the material that caused the bitter taste present in sea water.
Pliny the Elder

Roman natural philosopher and naval commander Pliny the Elder (25-76AC) in his fundamental work “Naturalis Historia” in Chapter 104 “Why the sea is salt”, presents Aristotele’s discoveries and gives qualitative description of salinity distribution with depth: “Hence it is that the widely-diffused sea is impregnated with the flavor of salt, in consequence of what is sweet and mild being evaporated from it, which the force of fire easily accomplishes; while all the more acrid and thick matter is left behind; on which account the water of the sea is less salt at some depth than at the surface.” In his explanation Pliny followed Aristotle, and helped to open up magnificent arena for the scholastics of the Middle Ages to dispute in. Pliny appears to have been the first person to give an early quantitative estimate for the amount of salt in sea water by which one could make sea water: “If more than a sextarius of salt is dropped into four sextari of water, the water is overpowered, and the salt does not dissolve. However, a sextarius of salt and four sextari of water give the strength and properties of the saltest sea. But it is thought that the most reasonable proportion is to compound the measure of water given above with eight cyathi of salt. This mixture warms the sinews without chafing the skin.” As in a case of Aristotle, Pliny thought the salt content should be greater at the surface due to the loss of water here. Yet along with Aristotle Pliny knew that salt water was more dense than fresh water, and he indicates that patches of fresh water can be found floating on the surface of the sea.
Seneca

Another Roman and contemporary of Pliny was the philosopher Lucius Seneca (3BC-65AD). Seneca’s view as to the nature of the world appeared in his Quaestiones Naturales. Seneca was a keen observer, and much of the Quaestiones Naturales present his own observations with more originality than, for example, Pliny. Seneca had noticed that the water level and the salinity of the sea remained constant even though water was constantly being added by rivers and rain. The constancy was, he believed, due to the evaporation of the sea’s waters. He believed that saline waters could be filtered by earth and attributed the formation of calcareous tuffs to this action. Seneca thought that the world in the beginning was characterized by a primordial ocean, and the substances dissolved therein separated out over some space of time. Although he know that solubility of a substance was in some way related to the water’s temperature and that the temperature of the sea varied, he seems to have believed that the ocean’s saltiness was a constant.
Bishop Watson says: “There are few questions respecting the natural history of the globe which have been discussed with more attention, or decided with less satisfaction, than that concerning the primary cause of the saltiness of the sea. The solution of it had perplexed the philosophers before time of Aristotle; it surpassed his own great genius, and those of his followers who have attempted to support his arguments have been betrayed into very ill grounded conclusions concerning it. Father Kircher, after having consulted three and thirty authors upon the subject, could not help remarking, that the fluctuations of the ocean itself were scarily more various then opinions of men concerning the origin of its saline impregnation”.

Leonardo da Vinci

In the Renaissance period Leonardo da Vinci (1452-1519) in his famous The Notebooks in Note 946 “Refutation of the Pliny’s theory of the saltiness of the sea” polemicize with Pliny: “Pliny says, that the water of the sea is salt because the heat of the sun dries up the moisture and drinks it up; and this gives to the wide stretching Sea the savor of salt. But this cannot be admitted, because if the saltiness of the sea were caused by the heat of the sun, there can be no doubt that lakes, pools and marshes would be so much the more salt, as their waters have less motion and are of less depth; but experience shows us, on the contrary, that these lakes have their waters quite free from salt. Again it is stated by Pliny that this saltiness might originate, because all the sweet and subtle portions which the heat attracts easily being taken away, the more bitter and coarser part will remain, and thus the water on the surface is fresher than at the bottom; but this is contradicted by the same reason given above. Again, it has been said that the saltiness of the sea is the sweat of the earth; to this it may be answered that all the springs of water which penetrate through the earth, would then be salt. But the conclusion is, that the saltiness of the sea must proceed from the many springs of water which, as they penetrate into the earth, find mines of salt and these they dissolve in part, and carry with them to the ocean and the other seas, whence the clouds, the begetters of rivers, never carry it up. And the sea would be saltier in our times than ever it was at any time; and if the adversary were to say that in infinite time the sea would dry up or congeal into salt, to this I answer that this salt is restored to the earth by the setting free of that part of the earth which rises out of the sea with the salt it has acquired, and the rivers return it to the earth under the sea.”

Robert Boyle

Scientific work on ocean salts was first done by the celebrated British natural philosopher Robert Boyle in 1674 with his publication of “Observations and Experiments in the Saltiness of the Sea”: “The Cause of the Saltiness of the Sea appears by Aristotle’s Writings to have busied the Curiosity of Naturalists before his time; since which, his Authority, perhaps much more than his Reasons, did for divers Ages make the Schools and the generality of Naturalists of his Opinion, till towards the end of the last Century, and the beginning of ours, some Learned Men took the boldness to question the common Opinion; since when the Controversy has been kept on foot, and, for ought I know, will be so, as long as this argued on both sides but by Dialectical Arguments, which may be probable on both sides, but are not convincing on either. Wherefore I shall here briefly deliver some particulars about the Saltiness of the Sea, obtained by my own trials, where I was able; and where I was not, by the best Relations I could procure, especially from Navigators.”
“After all, (says he,) it may be observed, that we are inquiring into the cause of a phenomenon, which it may be said had no secondary cause at all. It is taken for granted, in this disquisition, that the water which covered the globe in its chaotic state, was not impregnated with salt as at present, but quite fresh: now this is an opinion concerning a matter of fact, which can never be proved either way; and surely we extend our speculations very far, when we attempt to explain a phenomenon, primeval to, or coeval with, the formation of the earth.”
Saltness of the Sea

This sensible writer then states the different experiments which have been made to discover the saltiness of the sea, round the shores of Britain; and proposes the following simple method of ascertaining it with tolerable certainty:”As it is not every person who can make himself expert in the use of common means of estimating the quantity of salt has g contained in sea water, I will mention a method of doing it, which is so easy and simple, that every common sailor may understand and practice it; and which, at the same time, from the trials I have made of it, seems to be as exact a method as any that has yet been thought of. – Take a clean towel, or any other piece of cloth; dry it well before the sun or before the fire, then weigh it accurately, and note down its weight; dip it in the sea water, and, when taken out, wring it a little till it will not drip when hung up to dry; weigh it in this wet state, then dry it in the sun or at the fire, and when it is perfectly dry, weigh it again: the excess of the weight of the wetted cloth above its original weight, is the weight of the sea water imbibed by the cloth; and the excess of the weight of the cloth after being dried, above its original weight, is the specific gravity of the salt retained by the cloth; and by comparing this weight with the weight of the sea water imbibed by the cloth, we obtain the proportion of salt contained in that species of sea water.” Whoever undertakes to ascertain the quantity of salt contained in sea water, either by this or any other method, would do well to observe the state of the weather preceding the time when the sea water is taken out of the sea; for the quantity of salt contained in the water near the surface, may be influenced, both by the antecedent moisture, and the antecedent heat of the atmosphere. And this leads to the consideration of a question proposed by Aristotle, – Why are the upper parts of the sea Salter and warmer than the lower? Some philosophers, admitting the fact, have followed him in attempting to explain it; whilst others have thought themselves authorized by experiment to deny the truth of the position; and those, perhaps, will argue with the greatest justness, who shall affirm that it is neither generally to be admitted, nor generally to be rejected, but that the sea in some places, and under certain circumstances, is saltier and warmer at the surface, than at any considerable depth beneath it, while in many others the reverse is true. The question consists of two parts, between which, though there probably is a connection, yet it is not so necessary a one as to hinder us from considering each part by itself. With regard to the use of this salt property of sea water, it is observed, that the saltiness of the sea preserves its waters pure and sweet, which otherwise would corrupt, and emit a stench like a filthy lake, and consequently that none of the myriads of creatures which now live therein could exist. From thence also the sea water becomes much heavier, and therefore ships of greater size and burden are safely borne thereon. Salt water also does not freeze so soon as fresh water, hence the Seas are more possible for navigation.
Boyle measured and compiled a considerable set of data for variations in the saltiness of surface seawater. He personally made a series of observations on the water of the English Channel, collecting it from various depths, and observing its specific gravity. He also designed an improved piece of equipment for sampling seawater at depth, but the depths at which it was used were modest: 30m with his own instrument, 80m with another, similar sampler. Boyle investigated the saltiness of the water by a number of processes: he tried the estimation of total solids by direct evaporation and ignition, but not being satisfied with result, he ultimately took the density as an index of the saltiness, and determined this either by means of a glass hydrometer, by weighting in a phial which was afterward weighted when full of distilled water, or by weighting a piece of sulphur in distilled water and sea water consecutively. His measurements of the salt in seawater were done also by precipitating the salt. He recommended the use of silver nitrate to determine the sweetness of all waters (Boyle, 1693). For the next century, no systematic studies of sea water salts were done using a common analytic scheme.

Louis Marsilli

Count Louis Ferdinand Marsilli (1658-1730) was the first actual marine scientist. For some years he served as a military officer aboard ship in the Mediterranean. Throughout most of this time he spent his leisure in the study of the sea. The methods Marsilli chose to analyze sea water were essentially those of Boyle’s. The chemical substances that Marsilli used were spirit of salt ammoniac and oil of tartar. Rather than using process of simple evaporation, he too, used distillation of known weight of sea water to produce the dry salt of the sea water. This was not uncommon by this time. These residues he weighted. Over period of time, in spite of all the care he took with the balance, he became convinced that the hydrometer was preferable in such measurements. Aside from inconsistencies in residue weights Marsilli had a consistent lightness in weight determined by balance. Marsilli believed the weight loss to be due to a loss of salt during the distillation caused by action of fire. The fire he believed actually consumed some salt. He found the same inconsistencies and lightness in using the balance to check saltiness of artificially prepared sea water.

Histoire Physique de la Mer

The Histoire Physique de la Mer was written by Marsilli and published in Amsterdam in 1725. Prior to the Histoire Physique de la Mer, no book existed that dealt solely with the sea from the scientific standpoint. This book of 173 pages with many accompanying plates covered all of the aspects of the sea. The first part dealt with the sea’s basin, the second with the water itself, the third the movements of the water, the fourth and the fifth marine plants and animals. Topics such as the nature of the bottom, saltiness, temperature, density, currents and color were treated. In the study of these he commonly made use of the hydrometer, microscope and balance. For density determinations at sea he used the hydrometer, as the balance was not reliable on board ship. The Histoire Physique de la Mer is truly remarkable book. As with most creative thinkers, Marsilli’s work is a complex mixture of the old and the new. While it was ahead of its time from the standpoint of ocean study its chemistry was characteristic of the period in which it was written. The use of data tables was not new in water analyses although Marsilli first used them in reporting of the large number of sea water analyses along with the location from which each sample was taken, and accompanying tide, current, temperature and time data, much like modern station data. He felt that many of the ocean parameters influenced other and took great care in his measurement. Prior to Marsilli virtually all sea water samples were performed by people other than the sampler and brought usually some distance to the analyst.
Antoine Lavoisier

Late in the 18th century, Antoine Lavoisier (1743-1794) used evaporation with a solvent extraction to obtain data for his analysis of sea water. In 1772 he wrote a paper on the use of alcohol in mineral water analyses. In it he chose to include the first analysis of sea water ever published. Sea water, according to Lavoisier, was a mineral water, but the most complicated one that he had examined. The analysis of sea water was essentially this. Lavoisier evaporated the total volume of water slowly to dryness by means of a “feu de lampe” in a “capsule de verre”. In the drying process “selenite” and “sel gypseux” were precipitated naturally as the water became more concentrated. These salts were removed, dried and weighted. Alcohol was then added to the final dried saline mass and the “sel marin a base de sel d’Epsom” dissolved in it. The existing residue was then heated with a two-to-one mixture (by volume) of alcohol and water until completely dissolved. “Sel de Glauber” and “sel d’Epsom” crystallized from the cooled solution, and were dried and weighed. The remaining alcohol-water solution contained some “sel marin” and “sel marin a base de sel d’Epsom” which was again slowly evaporated, dried and weighed. Six years after the paper on the use of alcohol in water analyses Lavoisier wrote a short paper on the analysis of water from the Dead Sea. The procedure for analysis of the Dead Sea water was essentially the same as that used in the sea water analysis previously. In the course of this analysis Lavoisier used eight different mixtures of alcohol and water. Lavoisier is recognized as a major contributor to the chemistry of sea water, although he wrote only one article solely on this subject and included only one other analysis of sea water in his writings. Lavoisier was familiar with the precipitate formed in salt solution by the addition of “dissolution d’argent” (silver nitrate) and he, of course, knew that precipitate was “lune cornee” (luna cornea: silver chloride). He used this test as a rough indication of the saltiness of the liquids, but did not regard this test as useful.

Torbern Olof Bergman
Torbern Olof Bergman (1735-1784) in 1774 used evaporation and precipitation to carry out a detailed examination of all natural waters and developed a list of the substances that he had identified in sea water. He introduced the technique of weighing the precipitated salts to determine their concentrations (Wallace, 1980).
Joseph Gay-Lussac

Joseph Louis Gay-Lussac (1817) used titremetry to develop simple and accurate methods to determine the salts and concluded that the salt concentrations of open sea water were constant everywhere. Most of Gay-Lussac’s comments on the sea are contained in the article “Note sur la Salure de l’Ocean Atlantique” (Note on the Saltiness of the Atlantic Ocean). A number of seawater samples were gathered from the middle of the English Channel by Gay-Lussac himself. It not only shows his willingness to go to sea but his understanding that the chemist should take his own samples whenever possible. Evaporation-solvent-extraction continued to be the primary method of determining saltiness until Murray (1818) introduced the indirect method involving the precipitation of specific “acids and bases,” then inferring the constituents of sea salt. Gay-Lussac agreed with Murray that the total salt content of seawater could be determined by an analysis such as Murrays simply by the addition of the weights of the individually determined components; but he felt that for the determination of the absolute salt content only a simple evaporation would work: “but it is simpler and more exact to determine it by evaporation until a deep red. This procedure is done very conveniently in a matrass whose neck is tilted at an angle of about 45° and which is stirred continually while it is over the flame, as soon as the salts begin to precipitate, in order to avoid bumping. The boiling cannot throw anything outside, and the residue yielded weighs exactly the weight of the saline substances”. On the basis of his own values and those of others, he concluded that everything indicated that seawater contained at least “trois centimes et demi (three and a half percent) of salt matter– “. After much consideration, Gay-Lussac decided that the “salureâ” of the great oceans have very small variations, if it is not the same everywhere (1817).This is extremely important. This is the first precise pronouncement that the salinity of the open ocean (specifically the Atlantic) is nearly the same (Wallace, 2004).

Alexander Mercet

Between 1819-1822 Alexander Marcet (1770-1822) performed some of the first measurements of the concentrations of the major salts in seawater, and he also invented a sampling bottle capable of retrieving samples directly from the ocean depths. He discovered that the highly precise and accurate measurement of the chemical composition of seawater could be accomplished by gravimetric analysis. As Marcet summarized his method of analysis, the procedure was:
1. To ascertain the quantity of saline matter contained in a known weight of the water under examination, desiccated in a uniform and well defined mode; and to compare it with the specific gravity of the water.
2. To precipitate the muriatic acid from a known weight of the water, by nitrate of silver.
3. To precipitate the sulfuric acid by nitrate of barites, from another similar portion of water.
4. To precipitate the lime from the water.
5. To precipitate the magnesia from the clear liquor remaining after the separation of the lime, which have the best effect by phosphate of ammonia, or of soda, with the addition of carbonate of ammonia.
The soda, by this method, is the only which is not precipitated, and which, therefore, can only be inferred by calculation.
Marcet also proposed that seawater contained small quantities of all soluble substances and that the relative abundances of some were constant (a theory later to be known as Marcet’s Principle).

Georg Forchhammer

The concept of salinity was introduced by the Danish chemist Johann Georg Forchhammer in 1865. Forchhammer worked under great disadvantages: his samples of water were brought home by seafaring men from different parts of the world in corked bottles, and they were necessarily all taken from the surface or immediately beneath it. Forchhammer did not attempt to determine quantitatively all the elements that occur in sea water, but confined himself to the very accurate estimation of the principal salt components, such as chlorine, sulphuric acid, magnesia, lime, potash and soda. Georg Forchhammer found that the ratio of major salts in samples of seawater from various locations was constant. This constant ratio is known as Forchhammer’s Principle, or the Principle of Constant Proportions. One of the most interesting his scientific work “On the Constitution of Sea Water at Different Depths and in Different Latitudes” (1863) made an era in the history of ocean chemistry.

Sir John Murray

The most comprehensive early study of the composition of seawater was that made by W. Dittmar (1884) on 77 samples collected by chemist J.Y. Buchanan during the HMS Challenger Expedition (1872-1876).”The physical and chemical investigations conducted by Mr. J.Y. Buchanan, during the three and half years’ cruise of H.M.S. Challenger, are among the most important and valuable of the Expedition. Mr. Buchanan collected daily, with much care, samples of the surface water, and determined the specific gravity. At all Stations, a slip water bottle was attached to the sounding line, and the specific gravity of the specimen of bottom water thus collected was also ascertained. At every Station, where practicable, waters were collected from intermediate depths at 25, 50, 100, 200, 300, 400, and 800 fathoms [46, 92, 183, 366, 732, 1463 metre, red] from the surface, with a stop-cock water bottle attached to a separate sounding line, under Mr. Buchanan’s personal supervision. The specific gravity of these waters was also determined. The routine chemical work of the Laboratory consisted in boiling out the gases from, and in determining the carbonic acid in, as many samples as possible. A very large number of samples of sea-water were collected from the surface, bottom, and intermediate depths, and preserved in glass stopper bottles. These were either sent to home along with other collections from various ports touched at during the expedition or brought home by the ship. It is difficult to any one, except those who actually witnessed the daily work at sea, to form an adequate idea of the labor, skill, and continuous effort required to carry these observations in all sorts of weather, and to form, and bring home successfully, collections and observations like those which have resulted from Mr. Buchanan’s exertions. Shortly after return to England, Mr. Buchanan analyzed a number of the samples of gas which had been boiled out from the waters on board ship. As Mr. Buchanan was subsequently unable to proceed with the chemical work connected with the Expedition, the reminder of the gas samples (along with the results of those analyzed), the water samples, and Mr. Buchanan’s official journals, were entrusted by late sir C. Wyville Thomson to Professor W. Dittmar, F.R.S., with a request that he would undertake certain analyses of the gas samples and the waters. Professor Dittmar forwarded reports on his analyses at various times to the late Editor during the years 1878-81.

W.Dittmar

In the year 1882, Professor Dittmar undertook, at my request, to complete the gas and water analyses, and to prepare a Report on the whole of this investigations into the Composition of Ocean-Water, embracing the work done on board ship by Mr. Buchanan.” John Murray, Editorial Notes to Report of the Scientific Results of the Voyage of HMS Challenger during the years 1873-76, Physics and Chemistry,V1.

J.Y.Buchanan

With the exception of the early analysis as to the purity of a certain well-known soap, no results of an analytical laboratory have received more publicity and attention than the classical results obtained at the University of Edinburg by Dittmar on the waters collected by J.Y. Buchanan. Since then many investigators have become interested in the chemistry of the sea. “The importance of this result cannot be over emphasized, as upon it depend the validity of chlorinity-salinity-density relationship and, hence, the accuracy of all conclusions based on distribution of density where the latter is determined by chemical or indirect physical methods, such as electrical conductivity…” Sverdrup, Johnson, Fleming (1942)

2. Introduction of the International Standard Seawater
Martin Knudsen

Studies of ocean circulation, which were carried out later in 19th century, involved investigation the distribution of salinity. Attempts were made to measure salt content by heating to remove the water from the sample by evaporation. Simple drying was accompanied by losses of volatile compounds and the hydroscopic nature of the thick residue made the measurement of its weight very difficult. A dry residue method was offered as a solution; the seawater sample was evaporated and dried to a stable weight at 480° C after processing with hydrochloric acid. On this basis salinity was defined as “the total amount of solid material in grams contained in one kilogram of seawater when all the carbonate has been converted to oxide, all the bromine and iodine replaced by chlorine, and all the organic material oxidized”.
Accordingly there was a need for a better method of determination total dissolved salts then the tedious and unreliable one of evaporating a sample. In 1889 the International Council for the Exploration of the Sea named Martin Knudsen as chairman of a commission to study the problem of determination the salinity of seawater. Based on the premise of constancy of ionic ratios in seawater, the commission defined a “chlorinity” that could be determined by a simple volumetric titration using silver nitrate, to be used as a measure of salinity. Knudsen and his colleagues made measurement on samples of seawater from the different regions of the World Ocean and on the basis of comparison of nine determinations of salinity and chlorinity, proposed the formula:
S = 0.03 + 1.805Cl (1)
This served oceanographers for the next 65 years. In his proposal Knudsen stressed the importance of the measurement of salinity of seawater in physical, climatologically and biological investigations and maintained that the measurement could be carried out by titration with an accuracy of 0.04 ppm but that was not generally achieved by the method them in use. Usually a few titrations were carried out by weighing and all volumetric titration were then referred to these. Knudsen pointed out that titration by weighing was at that time a fairly difficult operation and the errors in salinity determination were usually as high as 0.1-0.2 ppm. Obviously, better accuracy could be obtained in salinity determination if all water samples were examined in one laboratory but Knudsen realized that this would not be very practical. Instead he proposed that all interested nations should contribute to the establishment of an institution for procuring standard water. This institution would prepare (and standardize in terms of its chlorinity) the standard water and distribute samples to interested laboratories, together with a statement of the physical and chemical qualities (properties) of standard.
Knudsen’s proposal has been reported in some detail on the Stockholm Conference in 1899. Persuasive though his arguments were, Knudsen’s proposal was not accepted in its entirety by the Conference. Despite his doubts, Knudsen’s arguments for a standard water evidently found favor with the members of the Conference, as it shown by the following quotation from the hydrographical program which they agreed upon. A footnote explains this further: … “By Standard water shall be understood samples of filtered seawater, the physical and chemical properties of which are known with all possible accuracy by analysis, and statements of which are sent to the different laboratories”. Thus, the need for standard water for use in all laboratories was established.
It should be stressed that preparation of standard seawater was nothing new for Knudsen. Prior to the Stockholm Conference he had made five different batches of such standards for use in Danish hydrographic work. About 80 tubes of standard seawater were prepared in April 1900 and were distributed to Russia, Sweden, Norway, Finland and Germany and were used for all Danish titrations until August 1902.

F.Nansen

The Central Laboratory from which standard samples would be sent, refers to proposal by Fridtjof Nansen, one of the Norwegian delegates to the Stockholm Conference. In meantime a second preparatory conference had been held in Christiania (Oslo) in 1901 at which Knudsen presented a provisional report on determination of the constants of seawater and then compilation of the Hydrographical Tables. In the hydrographic program the use of Knudsen’s Tables was directly prescribed. It was further prescribed that “The same standard seawater shall be employed in all cases for standardizing the solution used for chlorine determinations”. In the autumn of 1902 the Central Laboratory was opened, but unfortunately it had a relatively short life. In 1908 Nansen decided that he no longer wished to continue as director and it was decided to close down the Laboratory. The Council agreed that, whereas the further elaboration of special problems in future must be entrusted to the specialists of the various countries, there remained “practical charges, in which all the hydrographers are concerned, e.g., the preparation of normal (standard) water. It seems natural to hand over again to Docent M. Knudsen this task …” Knudsen agreed to direct, on behalf of the Council, the preparation and distribution of the standard seawater were transferred from the Central Laboratory to Copenhagen in September 1908, where it remained until it was transferred to England in 1974.

From the start of preparation of the standard has remained the same in principle though there have been some changes in detail. The water has usually been collected at the surface in the North Atlantic and transported in glass carboys or, more recently, polythene containers to the Standard Seawater Service premises. It is then pumped through filters into the storage tank and circulated through the filters for 2-3 weeks to achieve thorough mixing. During this period the seawater is gradually diluted with distilled water to give a final salinity near 35. For sealing the seawater in the glass ampoules the method used today is similar to the one described by Knudsen in 1903, though the scale is now much bigger of course.
3. Implementation of the electrical conductivity of seawater

Svante Arrhenious

A work of a chemical nature, while it had no direct reference to the sea water, was, nevertheless, important to an understanding of the chemistry of sea water by explaining the state of solution of the salts therein. This was the great Swedish chemist Svante Arrhenius’ (1859-1927) theory of electro-lytic dissociation. In short Arrhenius said that salts dissolved in water broke up into dissociated molecules. He further postulated the existence of electric charge of these dissociated parts. While the road was by no means easy, Arrhenius’ theory flourished. The difficulty in visualizing the state of a salt in solution was made easier. The scientific world was generally quick to use this theory. By 1910 Sir John Murray included in one of his book this definition: Ion – a form of molecular aggregation of matter in aqueous solution. An inorganic salt, base, or acid is partly split, when in solution, into ions. The metals mostly give cat ions, which carry a negative electrical charge and go to the positive pole in electrolysis. Acid radicals and certain non-metals form positively charged anions. In any solution the total negative charges on the cat ions exactly balance the total positive charge on the anions. It is impossible to isolate ions as such; when completed to assume the solid state, they combine with one another to give electrically neutral molecules. It was possible for oceanographers to “resolve” the constituents of sea water much more readily.
Hercules Tornóe

In the late 19th century a method was developed for determining the salinity of the seawater sample from measurement of its electrical conductivity. The Norwegian chemist Hercules Tornóe became a pioneer in this matter. At the meeting on 6 October 1893 of the Norwegian Academy of Science, he reported on the series of investigations which showed that salinity of the seawater could be determined by measuring the electrical conductivity of the water. The conductivity would be determined by means of alternating current and a telephone bridge. As conductivity is also greatly influenced by temperature, the temperature would have to be determined with great accuracy and its influence eliminated. Martin Knudsen went a step further by designing an instrument which, based on the same principle, made it possible to determine the salinity and temperature of the seawater without collecting water samples or pulling the thermometer out of the water. Through the method aroused considerable interest it did not really gain ground, undoubtedly because the underlying instrument technique was not sufficiently developed at the time.

Although the electrical conductivity of seawater had been used together with temperature for salinity determination since 1930, (Winer, 1930), precision salinometers based on this principle had to await the advent of modern electronics. In the late 1950s the measurement of electrical conductivity started to replace the chlorinity titration as a means of estimating salinity. Salinometers, incorporating high precision comparator bridges and thermostatically controlled baths, were developed to compare the electrical conductivity of the sample with that of standard seawater of known chlorinity (and hence salinity) at the same temperature. The measured conductivity ratio was then converted to salinity by means of relationships which had been established in 1934, (Thomas, Thompson, Utterback, 1934), but which were not of the desired quality. Cox has noted that there was an error in their extrapolation of measured values to 15°C but even after this was corrected unacceptable discrepancies were occurring between salinities calculated from conductivity ratio and temperature and those resulting from the application of (1) to a chlorinity titration.
New relationship between salinity, conductivity ratio and temperature were, therefore, established based on measurements carried out on natural seawaters covering a wide salinity range. Thus the chlorinity based salinity became re-defined in terms of conductivity ratio and at the same time the equation (1) was replaced by:
S = 1.80655 Cl (2)

This made both salinity and chlorinity conservative properties. Equations and tables based on the new measurements were published in 1966 by UNESCO and were widely adopted. Although the new conductivity/salinity relationships and definition of salinity helped to establish uniformity in salinity determinations, they had limitations. As they were originally intended for use with laboratory salinometers, they had a limited temperature range so could not be used for converting data from in situ instruments which were mostly used at temperatures below 10°C. Also the samples of seawaters used for the basic measurements were natural seawaters in which there were probably variations in ionic ratios which affected conductivity/chlorinity relationships. In addition, Standard Seawater used for all salinity determinations was certified only in chlorinity which was not satisfactory for a conductivity standard.
4. Development of the Practical Salinity Scale

The work aimed at the development of a uniform repeatable Practical Salinity Scale, based on electrical conductivity measurement, was undertaken in 1975 at the request of the UNESCO-SCOR-ICES-IAPSO, Joint Panel on Oceanographic Tables and Standards (JPOTS) in several different laboratories in four countries with radically different measurement equipment. The following groups were involved:
1. A.L. Bradshaw and K.E. Schleicher, Woods Hole Oceanographic Institution (WHOI), Woods Hole, USA;
2. F. Culkin and N.D. Smith, Institute of Oceanographic Sciences (IOS), Wormley, UK;
3. T.M. Dauphinee, J. Ancsin, H.P. Klein and M.J. Philips, National Research Council (NRC), Ottawa, Canada;
4. R.G. Perkin and E.L. Lewis, Institute for Ocean Sciences (IOS-C), Sidney, Canada;
5. A. Poisson, Laboratorie d’Oceanograpic Physique (LOP), Paris, France.
The work done to develop the scale could be presented in five parts:
1. Set up a reproducible primary standard of electrical conductivity, against which all future lots of standards and other standards could be measured. The standard chosen was the conductivity at 15°C of a solution of potassium chloride (KCl) in distilled water having a specified concentration chosen to give a conductivity ratio of 1 to current standard seawaters (referred to 35‰) at 15°C and normal atmospheric pressure. Determination of the standard concentration KCl and ancillary experiments to facilitate future work were carried out at IOS, NRC, and LOP. The standard seawater samples were supplied by the Standard Seawater Service at IOS and were known to be on the curve of conductivity (C) versus chlorinity (Cl) of recent batches, thus ensuring continuity of the scale at the transition date. The agreement among the three laboratories turned out to be as good as one could reasonably expect. The final values for KCl (IOS 32.4353, NRC 32.4356, LOP 32.4358 gKCl/kg solution have a spread of only 0.5 mg/kg [equivalent to 0.6 ppm S]).The average (rounded to 32.4356 g/kg) has been used by JPOTS in the definition of the Practical Salinity Scale 1978. Remarkable, this averaged value of KCl absolutely confirm the result, achieved by Dauphinee’s team from NRC.
Karl Schleicher

2. Determine the relationship between salinity and the ratio of the conductivity at salinity S to the conductivity of the standard seawater at different temperatures under atmospheric pressure. These measurements were carried out over the whole ocean range at NRC (0 < S < 42‰, -2 < t < 15°C) and LOP (4 < S < 42‰, -1< t < 30°C) and confirmatory data was supplied by WHOI. The NRC and LOP data are in total agreement over almost the entire range of overlap to the 1-ppm level, and are with few exceptions within the combined experimental error of the confirmatory data.
3. Determine the effect of temperature on the ratio rt of the conductivity of standard seawater (S=35‰).The function rt is required for most in-situ measurements where the measured quantity is the ratio of in-situ conductivity to the conductivity at 35‰, some reference temperature, usually 15°C and p = 0. These measurements were carried out at NRC and WHOI with confirmation from earlier work at NRC. The WHOI data lies between the two NRC sets and differs from the most-recent more-accurate set by substantially less than 1 ppm S, except at the highest temperatures.
4. Determine the effect of pressure on the conductivity of seawater over the full range of oceanic temperatures and salinities. This function is required to correct in-situ conductivity measurements to their zero pressure equivalents before the final calculation of the salinity is carried out. Equipment to measure conductivities under pressure to the accuracy required was only available at WHOI, and so all measurements were carried out there and it was not possible to get good independent confirmation of the Bradshaw and Schleicher data. However, confirmation was available from their earlier, almost universally used pressure data, since the new and old data sets are in excellent agreement. Also field checks by other workers have indicated there are no problems with the earlier data. The new equations are based on both sets of measurements.
5. Consolidate into a single set of equations the final experimental values as supplied by the various laboratories. These equations define Practical Salinity in term of the conductivity ratio at 15°C and give a mechanism for calculation of salinity from conductivity, temperature and pressure measurements. This part of the work was carried out at IOS-C as a “neutral party” not involved in the actual measurements, with suggestions as to appropriate forms of the equations from the groups involved and some check calculations at NRC. The outcome of this analysis has been a set of equations quite different in form from those previously in use which were shown to be inadequate to match the precision of the new experimental data base.
Neil Brown

In addition important confirmatory evidence not actually used to derive the scale was obtained from F. Millero, University of Miami, Miami,USA, and from earlier work of N. Brown and B. Alentoff, US Office of Naval Research, San-Diego, USA. One of the conditions for acceptance of any results was that there should be independent confirmation over most of the range of interest. It was decided that the measurements would be carried out on recent lots of standard seawater as supplied by the Seawater Service at the Institute of Oceanographic Sciences, Wormley, UK, weight diluted or concentrated as necessary using distilled water for all dilutions.
The definition of the scale, as reported by Lewis in the paper immediately following entitled, “The Practical Salinity Scale 1978 and Its Antecedents.” Equations of the Practical Salinity Scale 1978 (PSS-78) have been accepted by the groups involved and by JPOTS and were adopted by a large part of the International Oceanographic Community at the IAPSO meeting in Canberra, Australia, in December of 1979, by SCOR in September 1980, by International Oceanographic Commission of UNESCO in June 1980. PSS-78 is recommended for use by all oceanographers in reporting future oceanographic data. For a nearly 30 years the Practical Salinity Scale in service of Oceanography as sophisticated algorithm for computation and reporting of ocean salinity data.

JPOTS Meeting in Sidney, Canada, 1980
Left-to-right: J. Crease, W. Kroebel, T. Dauphinee, F. Culkin, C. Ross, E. Lewis, J. Gieskes, S. Morcos, A. Poisson, O. Mamayev, F. Millero, N. Fofonoff, R. Perkin, F. Fisher, M. Ménaché.
Referencer:
1. Maury M: “On the Saltness of the Sea” (1855)
2. Report on the Scientific Results of the Voyage of the H.M.S. Challenger during the years 1873-1876. Physics and Chemistry. (1884)
Vol1:
I. Dittmar W: Report on Researches into the Composition of Ocean-Water, collected by H.M.S.Challenger, during the years 1873-1876.
II. Buchanan JY: Report on the Specific Gravity of Samples of Ocean-Water, observed on board H.M.S.Challenger, during the years 1873-1876.
III.Report on the Deep-Sea Temperature Observations of Ocean-Water, taken by the Officers of the Expedition, during the years 1873-1876.
3. Buchanan JY: Comptes Rendus of Observation and Reasoning. (1917)
4. Herdman WA: Founders of Oceanography and their work. (1923)
5. Sverdrup HU, Johnson MW, Fleming RH: The Oceans. (1942)
6. Stuart RH: Introduction to Physical Oceanography. (2003)
7. UNESCO technical papers in marine science #37
“Background papers and supporting data on the Practical Salinity Scale 1978”
8. UNESCO technical papers in marine science #62
“Salinity and density of seawater: Tables for high salinities (42 to 50)
9. Park K, Burt WV: Electrolytic Conductance of Sea Water and the Salinometer. (1965)
(Part 1)
10. Park K, Burt WV: Electrolytic Conductance of Sea Water and the Salinometer. (1965)
(Part 2)
11. M.C.Stalcup MC: Salinity Measurements. (1991)
12. Shkvorets I, Johnson F: The Performance of the New Micro-Salinometer MS-310. (2007)
13. Shkvorets I, Johnson F, Yashayaev I: A New Method of Salinometry. (2009)
www.salinometry.com
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Salinimetry – Methods of Determination of salinity

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Salinimetry – Methods of Determination of salinity 110824-1

Determination of salinity, as the total measure of inorganic dissolved matter, is by evaporation of the water and weighing of the residue. This is a difficult process, because some carbon dioxide and hydrogen chloride escape during the evaporation process and corrections must be made for this. Furthermore, at sea methods involving weighing cannot be used. So the methods to be applied on board a ship have to be indirect ones. In the past century only two major methods have been used in the oceanography for measurement of the seawater samples salinity: chlorinity titration and conductometry.
1. Chlorinity Titration
Chemical determination of halide content by titration was for many years the usual routine method for determining the “sea salt” content of sea water samples.
Karl Mohr

This method, which known as Mohr method (Mohr, 1856), consist of titrating a sample of seawater with silver nitrate solution of known concentration to the point where all halides (chloride plus a small amount of bromide ) have been precipitated as silver halide, as detected by suitable indicators or electrode systems. A 15ml Knudsen pipette is used to measure the sea water sample into the titration vessel. This pipette differs from the standard type in that, after filling, the volume of sample is defined by rotation of a 3-way stopcock fitted at the upper end.
The titrant used in Mohr method is silver nitrate:

Cl- + Ag+ = AgCl

Usually most of the silver nitrate is added as a strong solution, to just short of the end-point , and then the titration is completed with a more dilute solution of silver nitrate. The other halides present are similarly precipitated. Potassium chromate is added as an indicator so that, when the halides have been titrated to a low level at the end point, silver chromate is precipitated:

2 Ag+ + CrO42- = Ag2CrO4

The titrant is normally added from the Knudsen bulb burette. Again, this is designed so that it can be used for routine analysis at sea; the burette is filled by gravity from a large storage container, and a zero mark is defined by a three-way stopcock at the top, as in the Knudsen pipette. Since most open-ocean samples lie in a relatively small chlorinity range, the burette is designed so that much of its capacity is in the bulb. This allows the scale to be graduated in increments of 0-0.02 ml to improve precision. Chlorinities between 16‰ and 21‰ can be determinent using silver nitrate solution of 36.75g/l; outside this range the titrant strenght must be adjusted to that the titre falls on scale.

Before titration commences, five drops of 10% potassium chromate solution are added to the sample. The silver nitrate is then added as a fine stream from the burette, with strong magnetic stirring to break up the silver chloride flocs. The endpoint is indicated by the precipitate turning pale brick-red for more than 30sec after addition of the last drop increment of silver nitrate.
The silver nitrate solutions are calibrated against IAPSO Standard Seawater certified in chlorinity (nowadays only in K15)

Knudsen Burette

The chlorinity of the unknown seawater is calculated as follows:
Clu = Cls × Tu × Ws \ Ts × Wu
where:
Clu and Cls – chlorinity of unknown and standard,
Wu and Ws – weight of unknown and standard,
Tu and Ts – silver nitrate titre for unknown and standard.
A modification of the Knudsen titration has been suggested by the Grasshoff and Wensk (1972). This uses a Metrohm incremental piston burette in place of Knudsen burette; the absence of greased stopcocks from the system is stated to improve markedly the convience and accuracy of shipboard analysis.
Potentiometric end point determination has been utilized by several workers to enhance the precision of the silver nitrate titration. Reeburgh and Carpenter (1964) used a differential electrochemical system for end point detection.
One of the major drawbacks of manual titration methods lies in the time taken per sample and the operators skill required. A semi-automatic method of chlorinity titration has been described (Jarner and Aren,1970) which reduces the time per sample to 5min while retaining high precision (0.004‰ in chlorinity).

Chlorinity was then converted to salinity by means of equation [1] or later equation [2] , prior to the introduction of the Practical Salinity Scale 1978. Chlorinity is now regarded as an independent chemical parameter to describe the properties of seawater and has no defined relationship to salinity.

2. Electrical Conductivity.
In the past fifty years, the chlorinity titration, which was time-consuming and required a certain degree of analytical skill, has been largely replaced by the measurement of electrical conductivity as a mean of estimating salinity.

The laboratory method consist of comparing by use salinometers the electrical conductivity of the sample with that of a standard (IAPSO Standard Seawater) of known salinity at the same temperature.
The measured conductivity ratio is than converted to the practical salinity by means of the equation of the PSS-78