304 



Alf Trolle. 



The titration was the usual chlorine titration as carried out by 

 the international investigations. For this purpose, as is known, a 

 solution of silver nitrate and potassium Chromate is used as indicator. 

 The following, detailed description may be of interest possibly to the 

 non-experts. 



With a so-called pipette ca. 15 gm. of the sample to be invest- 

 igated was poured into a clean tube and then some drops of potas- 

 sium Chromate solution added. From a graduated burette the silver 

 nitrate solution was now run drop by drop into the tube. 



The silver nitrate combines with the chlorine of the sea-water and 

 a white precipitate of silver chloride is formed. As soon as all the 



Fig. 7. Installation оГ the instruments for titration \vorl<; С B. Thestrup phot. 



chlorme is used up, the silver nitrate begins to act upon the potas- 

 sium Chromate and the liquid is coloured red. 



Thus, a distinct change of colour occurs, as soon as all the 

 chlorine is combined in the silver chloride and the quantity of silver 

 nitrate necessary for this purpose is read off on the burette. 



A quantity of normal water, that is, water in which the amount 

 of chlorine had been very exactly determined beforehand, was obtained 

 from the Central Laboratory in Christiania for use on the Expedition. 



On investigating how much silver nitrate was required to neu- 

 tralize the known amount of chlorine of the normal water, the amount 

 of chlorine in the unknown sample could now be determined by the 

 proportions between the readings. 



