ESTIMATION OF IRON, ALUMINA AND PHOSPHORIC ACID. 169 



shorter method of analysis is certainly much to be desired. 

 Aiming at this object, I have suggested the following 

 method, which appears to me to greatly lessen the amount 

 of work and time occupied in obtaining the desired results. 



The method is an adaptation of those previously made 

 use of, but as the amount of phosphoric acid already in 

 solution is an unknown quantity, another factor has to be 

 sought in carrying out the calculation. This is supplied 

 by the weight of the mixed phosphates of iron and alumina. 

 The method is as follows: — To the solution, which must be 

 sufficiently acid to produce a yellow colour and not a reddish 

 one with the iron present, is added a definite quantity of a 

 standard solution of sodic dihydric phosphate. In case the 

 original solution is too strongly acid, this can be partially 

 neutralized by caustic potash or by evaporation ; and it is 

 convenient to work with 20 or 30 cc. of solution containing 

 not more than '1 gm. of the mixed oxides. With this 

 amount of liquid, the precipitation can be conveniently 

 carried out in a 100 cc. flask. Caustic potash of decinormal 

 strength is gradually run in under constant shaking until 

 the pink tint with methyl orange has just disappeared. 

 The volume is made up to 80 or 90 cc. and warmed for a 

 short time on the water bath. This heating causes the 

 precipitate to coagulate and quickly settle. The precipit- 

 ate is now filtered off and well washed with hot water 

 until the filtrate gives no cloudiness with silver nitrate 

 when tested for chlorides, assuming them to be present. 

 A few more washings after this stage is arrived at, 

 thoroughly stirring up the precipitate on the filter, are 

 then sufficient. The filtrate and washings together will 

 then make 200 or 250 cc. Calcium chloride in excess is 

 added, the whole made slightly acid to methyl orange by a 

 few drops of decinormal hydrochloric or sulphuric acid, and 

 boiled to get rid of any carbonic acid. The procedure is 



