METHOD OF DETERMINING IRON IN WATERS. 347 



The standard solutions and materials required are as 

 follows : — 



'i) Standard Iron Solution. This is prepared by weigh- 

 ing out 07 grm. of ammonio-ferrous sulphate ( = o - i 

 grm. Fe), dissolving in water, and adding i cub. cent, of 

 the sulphuric acid ; the iron is next oxidized by adding 

 an exact sufficiency of the potassium-permanganate solu- 

 tion from a burette, and the whole diluted to I litre. Of 

 this solution i cub. cent. = o'oooi grm. Fe. 



(2) Solution of Potassium Permanganate. This must 

 be moderately dilute ; but it is not necessary that it should 

 be of standard strength. 



(3) Standard Nitric Acid. Is prepared by diluting 50 

 cub. cent, of pure strong nitric acid to 1 litre. 



(4) Potassium-Ferrocyanide Solution. Is obtained by 

 dissolving 1 part of the salt in 25 parts of water. 



(5) Strong Sulphuric Acid diluted with an equal volume 

 of water. 



(6) Two similar glass cylinders and a glass rod. The 

 former should hold rather more than 200 cub. cent, each, 

 the point equivalent to that measure being marked on the 

 glass. 



(7) A burette marked to o*i cub. cent, for the iron solu- 

 tion, and an ordinary burette for the permanganate. 



(8) Three 1 cub.-centim. pipettes for the ferrocyanide, 

 nitric acid, and sulphuric acid respectively, the one for the 

 last being marked also to deliver 0*5 cub. cent. 



The following is the method of analysis employed : — 

 A measured quantity of the water less than 1 litre in 

 bulk is taken, the amount being regulated according to 

 the quantity of iron contained in the water, which is 

 judged by a previously made qualitative experiment of 

 adding 1 cub. cent, of the ferrocyanide to a portion of the 

 oxidized water. One cub. centim. of the sulphuric acid is 

 added, and then the permanganate from a burette till a 



2 a 2 



