196 



Sanitary Studies of Baking Powders 



In Order to ascertain whether correct results were obtainable by 

 this procedura, a sol. of a very pure potassium alum was prepared 

 and standardized. This sol. was found to be free from phosphate 

 and to contain a negligible trace of iron. The standardization of 

 the sol. was effected by precipitating the aluminium as hydroxid, in 

 the presence of ammonium chlorid, with a current of ammonia gas 

 and removing almost all the ammonia by boiling. The hydroxid 

 was filtered off, washed, re-dissolved in a little hydrochloric acid 

 sol., then re-precipitated as before, and finally ignited and weighed 

 as AI2O3. The analytic data are appended. 



Volume of Solution taken. 



CC, 

 50 



25 



Found. 



mg. 



194-3 

 97-5 



Weight of AI2O3 . 



Per CC. 



mg. 



3.89 



3-90 



The Schmidt-Hoagland method was then applied to portions of 

 the same sol., with the results summarized below: 



From these figures it is evident that the Schmidt-Hoagland 

 method may give results involving a loss of as much as 7 percent 

 of the available aluminium. The average error was about 4 per- 

 cent. In determinations of very small amounts of aluminium, say 

 less than 3 mg., a loss of 7 percent might fall within the ränge of 

 error of an ordinary analytical balance, and would be insignificant. 



Altho the indicated error is relatively unimportant, in determi- 

 nations of small amounts of aluminium in biological materials, we 

 endeavored, nevertheless, to ascertain its cause. 



