202 Sanitary Studies of Baking Powders 



The fact that the masses of phosphate could be ignited to con- 

 stant zveight, after a preliminary production of oxid, suggests that 

 a "surface layer" of the oxid protected the remaining phosphate 

 from further decomposition, 



CoNCLUsiONS. The Schmidt-Hoagland method for the deter- 

 mination of aluminium gave results which involved a loss of as 

 much as 7 percent of the available aluminium, but which was 

 usually about 4 percent. 



The losses appear to have been due, in the main, to the forma- 

 tion of AI2O3 from AIPO4, in the precipitate of the latter during 

 ignition, but also partly to the solubility of AIPO4 in the reagents 

 and washings. 



The material, as finally weighed, is not wholly normal ortho- 

 phosphate of aluminium, but contains less phosphoric anhydrid than 

 does the same weight of ortho-phosphate. 



The indicated error might invalidate the method for accurate 

 determinations of relatively large amounts of aluminium. For 

 comparatively small quantities, however, the error appears to be 

 negligible. 



