BY DR. BURDON-SANDERSON. 203 



solved in pure dilute hydrochloric acid, and the iron deter- 

 mined volumetrically with permanganate of potash. This is 

 accomplished as follows : 



The volumetrical solution of permanganate which is usual- 

 ly employed, is prepared by dissolving the pure crystals in 

 distilled water, in the proportion of 3.16 grammes to the litre. 

 It is of such strength that 17.85 centimetres correspond ap- 

 proximatively to one-tenth of a gramme of metallic iron. It 

 is, however, necessary, before using it, to determine its exact 

 strength, by means of a weighed quantity of solution of the 

 double sulphate of iron and ammonia. The mode of preparing 

 this salt will be found in Button's " Volumetrical Analysis." 

 It contains exactly one-seventh of its weight of iron, so that 

 0.7 gramme represents 0.1 gramme of iron. The mode of ap- 

 plying it is as follows: 



0.7 gramme of the salt having been dissolved in a beaker in 

 distilled water, and five or six c. c. of dilute (1 : 5) sulphuric 

 acid added, the permanganate solution is delivered from a bu- 

 rette, having a glass stopcock, until a point is reached at which 

 the rose coior no longer disappears on shaking. As the per- 

 manganate must be slightly in excess to produce a percepti- 

 ble color, a correction should be made by ascertaining experi- 

 mentally how much of the salt is required to produce the 

 observed intensity of color in the quantity of liquid used. 

 This quantity should then be deducted from the result. The 

 number of cubic centimetres used for 0.7 gramme of the 

 double sulphate, (i. e., 0.1 gramme of metallic iron) must be 

 marked on the bottle. As the method depends on the con- 

 version of the iron from the lower to the higher stage of oxi- 

 dation at the expense of the permanganate, it is obviously 

 necessary that the whole of the iron in the liquid to be ope- 

 rated upon should be in the condition (to use modern lan- 

 guage) of a ferrous salt. For this reason, the first step in 

 dealing with the hydrochloric acid solution of blood ash, is to 

 reduce it. With this view, the solution of ash is first intro- 

 duced into the flask already mentioned, in which it is gently 

 boiled with a few pieces of zinc until the latter is dissolved 

 and the liquid is colorless. It is then allowed to cool and 

 diluted to fifty centimetres, after which the solution of per- 

 manganate is added to it from the burette, as before, until 

 the rose color becomes permanent after agitation. For each 

 centimetre of the red liquid emplo3 r ed in attaining this result, 

 the quantity of solution in the flask contains 0.0056 gramme 

 of iron. 



