SANITARY STUDIES OF BAKING POWDERS 



7. A direct test of the degree of accuracy o£ the Schmidt-Hoag- 

 land method for the quantitative determination of 



aluminium 



ARNOLD K. BALLS 



(Biochemical Laboratory of Columbia Umversity, at the College of Physicians 



and Surgeons, New York) 



(Received for publication, December i, 1915) 



Prior to the inauguration of a study of the absorption of alu- 

 minium from aluminized foods, we tested directly the accuracy of 

 the Schmidt-Hoagland^ method for the determination of aluminium 

 — the method we expected to use in the investigation.^ This method 

 is conducted, in principle, as follows: The organic matter is de- 

 stroyed, silica dehydrated and removed, and ammonium phosphate 

 added to the aluminium-containing sol., which is acid with hydro- 

 chloric acid. The sol. is then neutralized with an excess of am- 

 monium thiosulfate, followed by the addition of ammonium acetate 

 and acetic acid. The aluminium is precipitated as the phosphate, 

 accompanied by large proportions of sulfur; while any iron that 

 may be present, being in the ferrous condition, remains in Solution. 

 The phosphate thus obtained is purified by re-precipitation accord- 

 ing to the original plan, and then is ignited to constant weight in a 

 silica dish.^ The advantages of this method, in the analysis of 

 biological materials, arise from the facts that iron is conveniently 

 excluded, that phosphates do not interfere, and that a direct deter- 

 mination of the aluminium is possible. 



^ Schmidt and Hoagland : Jour. Biol. Chem., 1912, xi, p. 387. 



2 Gies : Biochemical Bulletin, 1916, v, pp. 151 and 189. 



3 Silica dishes, even of the " clear " variety, last but a short time, repeated 

 ignitions causing them to " scale off " on the exterior. In these tests ordinary 

 crucibles of German porcelain were used with entire satisfaction ; they withstood, 

 without loss of weight, the temp's of ignition to which the precipitates were 

 subjected. 



195 



