WATER ANALYSIS 59 



Solutions required : (a) Ferrous sulphate solution (5 per 

 cent in i per cent H 2 SO 4 ) ; (b) Standard potassium per- 

 manganate solution (5-638 grm. per litre), I c.c. = I c.c. 

 oxygen at normal temperature and pressure ; (c) Ltd. 

 pot. bichromate solution (879 grm. per litre), i c.c.= I c.c. 

 oxygen at normal temperature and pressure ; (d) Sulphuric 

 acid, 50 per cent in distilled water. 



PROCESS. Measure the exact capacity of the large bulb. 

 Fill it by siphonage to avoid absorption of atmospheric 

 oxygen. Insert stopper and drain off excess of fluid. 

 Remove stopper, withdraw 7 c.c. of fluid, add 5 c.c. of 

 ferrous sulphate solution by pipette to bottom of bulb, 

 fill up mouth with strong ammonia solution, and insert 

 stopper. Mix by swinging. A precipitate of greenish 

 ferrous hydrate forms, which absorbs dissolved oxygen, 

 becoming brownish ferric hydrate. Allow to stand fifteen 

 minutes. Then add 50 c.c. of the sulphuric acid solu- 

 tion to the small bulb, and opening the stopcock 

 allow it to mix into the larger bulb. The hydrates are 

 dissolved, and sulphates formed. Pour out into a beaker, 

 and titrate with permanganate in case of water, and with 

 bichromate for sewage. For latter, end reaction is got 

 by removing a drop of liquid from the beaker, and touch- 

 ing a drop of solution of potassium ferricyanide, when if 

 oxidation is incomplete, a blue colour (Turnbull's blue) is 

 produced within two minutes. A control or preliminary 

 titration is made by taking the same quantity of sample 

 (less 7 c.c.), adding first 50 c.c. of the sulphuric acid, then 

 5 c.c. of the ferrous sulphate solution, and then titrating. 

 The end of the titration with permanganate is a permanent 

 faint pink tint. 



The Sewage Commission recommend that the suspended 

 solids should be removed before estimating the dissolved 

 oxygen, because " small variations in the amounts of solids 

 in suspension in effluents may seriously affect the rate at 

 which effluents take up oxygen." 



Kjeldahl's Method for Total Nitrogen. Owing to the 

 large amount of organic matter in sewage, the estimation 

 of albuminoid ammonia is alleged to be unreliable, and 

 the estimation of the total nitrogen is preferred. 



