Matthew Steel 



177 



consists in determining the weight of the combined iron and aki- 

 minum phosphates according to the technique of the A.O.A.C. 

 method, then determining the iron content by the Mixer and Du- 

 Bois (11) modification of the Zimmerman-Rheinhardt permanga- 

 nate method in an ahquot portion of the original acid sol. A 

 " blank " is made on the reagents used in the method and the " weight 

 of the blank" is added to the amount of FeP04; this weight is then 

 subtracted from the combined weights of AIPO4 and FePO^. See 

 Table 2. 



TABLE 2 



Data pertaining to the estimation of aluminum by Steel's method 



7. Estimation of iron and aluminum by the Government 

 Research Committee method (12). This method is very simi- 

 lar to the modified A.O.A.C. method used by Steel (13). How- 

 ever, there are a few minor differences which are worthy of note, 

 the most important of which are the following: 



A. — The use of ammonium phosphate instead of sodium phos- 

 phate. 



B. — Performing the acid digestion of the iron and aluminum 

 phosphates in flasks made of glass containing little 

 alumina, such as " Kavalier " er " F-Z resistant glass."* 



* This committee was estimating the iron and aluminum content of phosphate 

 rock, which contained more or less fluorin. They condemn the use of glass con- 

 taining a relatively high percentage of alumina on account of the solvent action 

 of the fluorin. This precaution is of little moment in the estimation of aluminum 

 in animal tissues or foodstuffs, as fluorin is rarely if ever present in these sub- 

 stances. 



