L. J. Curtman and P. Gross 167 



iron titer of the sol. changed slightly. This was corrected by re- 

 standardizing the sol. at the time it was used for the determination 

 of the iron value of the blood. 



FeCl^ sol. Five 1. of a sol., i cc. =: i mg. of Fe (approximately) 

 containing i percent of HCl (sp. gr., 1.2) was standardized as follows: 



(a) Fifty cc. were evaporated in a porcelain dish with 5 cc. of 

 H2SO4 (sp. gr., 1.84) until SO3 fumes were produced, then transferred 

 to a weighed platinum dish, evaporated to dryness and ignited to Fe203 

 at a low red heat. 



(&) Titration of 10 portions (5 of 25 cc, 5 of 50 cc.) against the 

 Standard KMnO^ sol. by the modified Zimmerman-Rheinhardt method. 



The results of these 11 determinations did not vary by more than 

 O.Ol mg. for the value of i cc. in terms of iron. The mean of these 

 II experiments gave a value of i cc. = 1.098 mg. for the iron sol. 



Comparison of methods. Of the methods proposed for the 

 determination of aluminum in biological material, two deserve con- 

 sideration; they are the method of SteeP and that of Schmidt and 

 Hoag-land.^ 



*^t>' 



Steel's method.* " Obtain an aliquot portion of the available 

 acid sol. (after oxidation) and remove any contained silica. Mix the 

 liquid with sodium phosphate sol. in excess of what is required to form 

 normal aluminum phosphate. Add sufficient ammonium hydroxide to 

 effect complete precipitation of the aluminum phosphate after thorough 

 stirring. Then add hydrochloric acid sol., drop by drop, until the 

 precipitate completely dissolves. Heat the liquid to about 50° C. and 

 mix with it, at that temperature, a considerable excess of 50 percent 

 ammonium acetate sol. and also 4 cc. of 80 percent acetic acid sol. 



2 Steel : Amer. Jour. of Physiol., 191 1, xxviii, p. 96. 



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



*The method proposed by Steel, although a modification of the official 

 method (U. S. Dept. of Agric, Bull. 107, p. 177), contains a sufficient number 

 of novel features to Warrant its consideration as a separate method. We have, 

 therefore, designated it throughout this article as Steel's method. Compared 

 with the official method, the procedure used by Steel is decidedly shorter and 

 as its shortcomings are not apparent, our experimental study was confined to a 

 comparison of the Schmidt-Hoagland method with that of Steel, instead of 

 with the official method. 



