i6o Sanitary Sfudies of Baking Powders 



of ammonium thiosulfate (in sol.) and, after several minutes, 6 to 8 

 gm. of ammonium acetate (in sol.) and 4 cc. of strong acetic acid are 

 added. Heating is continued for about half an hour to expel SO2, 

 the precipitate allowed to settle, filtered and washed once by decanta- 

 tion. The precipitate is redissolved in 2 to 2.5 cc. of conc. hydro- 

 chloric acid, the sol. diluted to about 300 cc, 0.5 gm. of ammonium 

 phosphate added for each 100 mg. of aluminum phosphate present 

 and the aluminum precipitated as described above. The precipitate 

 is filtered and washed several times with hot water to remove Chlorides, 

 and ignited in a transparent silica crucible until constant weight is 

 reached to remove excess of P0O5." 



Experimental. As a preliminary procedure, blank determina- 

 tions were carried out with both methods on dist. water, using the 

 quantities of Solutions and reagents required for the precipitation of 

 approximately 10 mg. of aluminum phosphate. The accompanying 

 results were obtained (Table i) : 



TABLE I 



Comparative data pertaining to the weights of material obtained in blank de- 



terminations 



A. O. A. C. (Steel) Method Schmidt-Hoagland Method 



Milligram Milligram 



1.0 0.7 



0.6 0.6 



0.8 0.6 



0.8 0.6 



0.9 0.5 



Sol. of pure aluminum sulfate and ferric chlorid were used in 

 comparing the two methods under investigation. Quantities of alu- 

 minum sulfate sol. were weighed out such that the weight of alu- 

 minum phosphate obtained upon precipitation would be approxi- 

 mately 10 mg. When ferric chlorid was added it was in amounts 

 which gave approximately 20 mg. of the phosphate. 



Aluminum sulfate. Analysis of the aluminum sulfate sol. 

 gave the results in Table 2 : 



