Paul E. Howe 163 



Goat blood. Samples of dry, pulverized goat blood, obtained in 

 the market and of doubtful purity, were oxidized as above, after the 

 addition of weighed amounts of the almiiinum sulfate sol. The 

 analytic results in Table 5 were obtained. 



Discussion and conclusions. Data have been presented showing 

 the comparative results obtained with two methods for the determi- 

 nation of aluminum in the presence of iron; the method proposed 

 by the Assoc. of Official Agric. Chemists as modified by Steel, and 

 that described by Schmidt and Hoagland. The comparison is on 

 the basis of small amounts of aluminum (equivalent, approximately 

 to 10 mg. of aluminum phosphate or 4 mg. of aluminum oxide), such 

 as would probably be determined in the analysis of tissues.''^' ^ 



The results of the experiments show an agreement between the 

 two methods when aluminum is determined in sol. containing a pure 

 aluminum salt and in sol. containing mixtures of pure aluminum 

 and iron salts. The analysis of blood to which aluminum sulfate 

 had been added gave results which were slightly lower in the case 

 of the method proposed by the Assoc. of Official Agric. Chemists as 

 modified by Steel. 



Considering the two methods from the point of view of manipu- 

 lation, the method of Schmidt and Hoagland commends itself par- 

 ticularly. The combined precipitate of sulfur and of aluminum 

 phosphate is readily filtered off and washed. We experienced some 

 difficulty at the beginning of our experiments with regard to the 

 amount of ammonium acetate required for precipitation of the 

 aluminum. Not enough ammonium acetate was added to obtain 

 a precipitate (the presence or absence of small precipitates of alu- 

 minum phosphate would be masked by the sulfur) because of the 

 acidity of the sol. This difficulty disappeared as soon as the proper 

 conditions were once established. 



The method proposed by the Assoc. of Official Agric. Chemists, 

 as modified by Steel, presented considerable difficulty in the matter 

 of manipulation. Following the directions as given, we did not 

 always obtain complete precipitation at 50° C. It was necessary to 

 heat the filtrate to boiling to obtain the final traces of the phosphates. 



^ Steel : Loc. cit. 

 8 Kahn : Loc. cit. 



