i68 



Sanitary Studies of Baking Powders 



As soon as the precipitated aluminum phosphate (mixed with iron 

 phosphate) has sedimented, collect it on an ashless filter, wash it with 

 hot water, ignite it and then weigh the residue. In an aliquot portion 

 of the original acid liquid determine the amount of iron by the Zimmer- 

 man-Rheinhardt method.^ The calculated amount of FePO^ is then 

 subtracted from the weight of the mixed AIPO^ and FePO^." 



This method was followed with but one exception. Enoug'h 

 sodium phosphate was added to form an excess over that required 

 to form both AIPO4 and FeP04. This is a necessary correction 

 probably accidentally omitted from Steel's description. 



The results obtained by this method, with mixtures of FeCls and 

 Al2( 504)3, a^G given in Table 2. 



TABLE 2 



Data pertaining to results obtained with Steel's method 



(o) Ignited in porcelain. 

 parent silica. 



(b) Ignited in platinum. (c) Ignited in trans- 



The precipitations were made in a vol. of 300-400 cc. The 



precipitates were washed free of Chlorides only, no attempt being 



made to wash free of phosphates since this would have resulted in 



effecting the hydrolysis of the AIPO4 and FePO^.*^ The wash-water 



contained a small amount of sodium acetate to prevent as much as 



possible such hydrolysis. In Det'ns 3 and 4 (Table 2), the washing 



was not completed, the runnings giving a decided test. This was 



done to determine whether the losses as shown in Det'ns i and 2 



were due to hydrolysis during the process of washing free from 



" Mixer and DuBois : Loc. cit. 



^Caven: Jour. See. Chem. Ind., 1896, xv, p. 17; Cameron and Hurst: Jour. 

 Amer. Chem. Soc, 1904, xxvi, p. 885. 



