Matthew Steel 



i8i 



TABLE 5 



Data periaining to the comparative efficiency of ihe three methods {Steel's, Gov. 

 Research Cotnmitiee's, and Schmidt and Hoagland's) 



III. Discussion of the relative merits of the three methods: 

 accuracy and precision attainable in aqueous sol. and in the 

 presence of large amounts of organic matter. The accuraqr of 

 the results obtained by the phosphate methods is affected (a) by 

 varying conc. of mineral acids at the time of precipitation of the 

 iron and aluminum as phosphates, (b) by the presence of aluminum 

 in appreciable quantities in the glassware used, (c) by variations in 

 the relative proportions of iron to aluminum (the best results are 

 obtained when the proportion of iron to aluminum is about 2 to i ) , 

 (d) by the quantities of iron and aluminum contained in the portion 

 used for analysis (the most accurate results are obtained when the 

 combined iron and aluminum phosphates do not weigh over 100 

 mg.) and (e) hy the temp. to which the crticihles are heated (either 

 the blast lamp, the muffle furnace, or the Meker burner may be used 

 to effect this incineration with equal accuracy, but the author prefers 

 the Meker hurner). "^ 



* Italics were inserted by the editor of the Biochem. Bull. See page 169. 



