§ 52. IRON. 69 



must be in the form of a sulphate or a chloride, and the 

 solution should contain about 0.5 grm. of iron and an 

 excess of free sulphuric or hydrochloric acid and as little 

 nitric acid as possible ; heat the solution in a small, long- 

 necked flask placed in an inclined position, drop in a few 

 pieces of pure zinc, and conduct carbonic acid through 

 the flask in the same manner as described above, for dis- 

 solving the ferrous salt ; the ferric compound is reduced 

 to a ferrous salt by the zinc, with the evolution of hydro- 

 gen. When the solution is decolorized, and all the zinc 

 is dissolved, cool the liquid as quickly as possible by im- 

 mersing the flask in cold water, while carbonic acid is 

 still passing through, transfer the solution to a beaker, 

 rinse the flask into the beaker with a considerable quanti- 

 ty of water, and dilute the solution until it contains about 

 200 c.c. for every 0.2 grm. of iron supposed to be present ; 

 the solution must be more largely diluted if the salt was 

 a chloride, or was dissolved in hydrochloric acid, instead 

 of sulphuric. 



To this solution add the solution of permanganate in 

 the same manner as directed above, for the treatment of 

 the ferrous salt. 



The amount of iron m the quantity of solution taken 

 will be given by the proportion 



C ; F = C : X 

 7 

 in which C = the number of cubic centimetres of per- 

 manganic solution used in the trial with the known quan- 

 tity of ferrous salt, F = the weight of the ferrous salt 

 taken, C = the number of cubic centimetres of perman- 

 ganic solution used in the trial with the substance exam- 

 ined, and X = the amount of iron therein. 



The solution of potassic permanganate is most con- 

 veniently kept in a bottle provided with an ordinary 

 washing-bottle arrangement for filling the burette from 

 it • then the bottle need not be opened until empty, no 



