39 



the iodine and bromine content*of a sample of 

 Water from Lake Gairdner. 



By W. Ternent Cooke, D.Sc. 

 [Read April 12, 1917.] 



The courtesy of Mr. A. C. Broughton put me in possession 

 of about half a litre of brine which, according to the donor, 

 was the liquor left after evaporating about 4 gallons of lake 

 water and removing the salts, mostly common salt, which had 

 crystallized out. 



The liquor had a very faintly alkaline reaction, and was 

 very syruppy. 



For iodine about 20 c.c, and for bromine 1 or 2 c.c, 

 were sufficient, respectively, to give distinct qualitative tests 

 for these elements. 



The methods of analysis are essentially those given in 

 Treadwell-Hall (Analytical Chemistry, vol. ii., p. 617, 2nd 

 ed.). 



The brine was added to three times its volume of spirit, 

 and after standing about two days the crystals, almost pure 

 magnesium chloride, which, separated, were filtered off and 

 washed once with spirit. From the nitrate most of the spirit 

 was distilled off, and the remainder driven off by evaporation 

 in an open dish. The brine left solidified on cooling; it was 

 dissolved and made up to 1 litre. This litre of solution, 

 which will be referred to below as the "brine," represents, 

 therefore, 4 gallons (about 18 litres) of the original lake 

 water. 



Iodine. — An attempt, seemingly fairly successful, was 

 made first to estimate the iodine colorimetrically. Two 

 similar burettes (those with a tap at the side and a pro- 

 longation below the tap) were used. Into the first was put 

 40 c.c, say, of brine, and into the second the same volume 

 of distilled water. To each was added about 5 c.c. of 

 chloroform and one or two drops of "nitrose" (nitrosulphonic 

 acid). On shaking the first and allowing to stand the 

 chloroform took on a certain depth of colour, due to free 

 iodine. This tint could be matched fairly closely by adding 

 to the second tube measured amounts of T £o potassium iodide 

 solution, shaking and allowing to stand. Thus: — 



40 c.c. brine matched 0'3 c.c. of iodide. 



50 ,, ,, ,, 0-4 ,, 



Whence we find that 1 litre of lake water contains '00054 grm 

 iodine, or 1 lb. of iodine is found in 186,100 gallons. 



