\a('l as a standard; Ilcriiiaii ' and leather and Kilcv - liave reported 

 a potentioinetric melliod wliicli is \'('i\- rapid and jirecise. 



Comjxirisoii Technique: About 50 gi-ains of sea watci' of known ap- 

 proximate chlorinity were transferred to a 12o-]nl., giass-stoppered 

 Eilenineyer flask. A slight excess of acidified strong silver nitrate 

 solution, usually about 53 grams, was transferred to a similar vessel. 

 The silver nitrate solution, hereafter referred to as the AgNOslstrong), 

 was prepared to be ec|uivalent to ca. 18.29°/oo CI and later analyzed as 

 18.278°/oo CI equivalent. In a darkened room the two solutions were 

 condjined, mixed, and stored in a 500-nd. Erlenmeyer for ca. 10 hours. 

 Tlie total volume including washing from transferring was 250 to 300 

 ml. I sually four samples were run tln-ough at one time. Tlie solution 

 was decanted onto a filter and the precipitate washed five tunes with 

 acidified conchictivity water. Final fiUering was accomplished by 

 slight suction and the precipitate washed tw^o tunes with conductivity 

 water. The filtrate, ca. 500 ml., was ti'ansferred to a 600 nd. beaker 

 and the vohune r(>(hiced to 20-50 ml. on a water bath. After some 

 experimentation, very efficient evaporation was accomplished by im- 

 attended air baths heated by properly adjusted Fischer burners. After 

 this volume reduction, the slight excess of silver nitrate was titrated 

 volumetrically witli annnonium tliiocyanate (ca. 0.05 N) and l)ack 

 titratiHl witli weak silver nitrate using 2 nd. of a saturated, acidihetl 

 sohition of Ferric Alum (FeXH4(S04)2 ■ 12 H.O) as indicator. From 

 the quantity of XrT4S(\V, weak Ag.XO.s and the established ratios of 

 these volumes to a unit mass of AgX03(strong), the exact amount of 

 AgN03(str()ng) corresponding to a weiglied amount of sea-water 

 sample was cojnputed. The exjjression for cliloi-inity in sea water used 

 for this comparison technique is: 



CI °/ =19 374 ^~^^ ' ^'' 

 ^ /oo ^•'•■^^^Sample-Sp 



where P 2S and "Sample" ai'e I lie masses of Xoinial water and the 

 sample respectively; and S|) and Sc the amounts of silver nitrate re- 

 (juired to pi'ecii)itate all of the halides in the Xormal water and the 

 sample, respectivelv. The value 19.374 is the nominal chlorinity of 

 P 28. 



All weighings were double weighings and buoyancy connections were 

 made only for the "exact" techni(|ue described below as in the com- 

 ])aris()n techni(|ue the coi rect ions for buoyancy are always positive in 

 the inuncM'ator and (h'tiominaloi' and are api)roximateiy the same for 

 norjnal water and sea water as their density is almost the same. All 

 a|)j)arati were calibrated against an "S" class 10 gram mass, checked 

 by the Xational Bureau ol' Standai'ds. All solutions were made up 

 with reag(Mit gi'ade chemicals, nitrogen oxide U-c{^ II XO;,, conductivity 

 walei', and sealed with an e\a|)orat ion proof techni(|ue. Care was 



76 



