Paul E. Howe 159 



was then treated with a fairly large vol. of conc. sulfuric acid sol. for 

 the expulsion of the nitric acid and for the complete oxidation of any 

 residual organic matter. The sulfuric acid mixture was boiled for 

 at least 2 hr. after it became colorless, in order to eliminate NO,. The 

 residue was then dissolved in water, made up to vol., and the iron and 

 aluminium determined. 



Determination of iron and aliiminum: " Obtain an aliquot portion 

 of the available acid sol. and remove any contained silica. Mix the 

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

 form normal aluminium phosphate. Add sufficient ammonium 

 hydroxid sol. to effect complete precipitation of the aluminium phos- 

 phate 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 temp., a considerable excess 

 of 50 percent ammonium acetate sol. and also 4 cc. of 80 percent 

 acetic acid sol. As soon as the precipitate of aluminium phosphate 

 (mixed with iron phosphate) has sedimented, collect it on an ashless 

 filter, wash it with hot water, ignite it and then weigh the residue. 



" In an aliquot portion of the original liquid determine the amount 

 of iron by the Zimmerman-Rheinhardt^ method. The calculated 

 amount of FePO^ is then subtracted from the weight of the mixed 

 AIPO, and FePO,." 



In the analyses with this method the above procedure was fol- 

 lowed exactly as described. It was necessary, however, occasionally 

 to heat the filtrate to boiling in order to obtain a complete precipi- 

 tation of the phosphates. 



II. Schmidt and Hoagland give the following description of their 

 method : An aliquot portion of the sol. obtained after the oxidation of 

 the tissues according to the method described by Kahn^ (see above) 

 is measured into a beaker, the silica dehydrated and filtered off. The 

 filtrate obtained is diluted to " about 300 cc. and should contain ap- 

 proximately 2.5 cc. of conc. hydrochloric acid. Tin is precipitated 

 from the hot sol. by hydrogen sulfid and filtered off. Di-ammonium 

 hydrogen phosphate is added to the sol. — 0.5 gm. for each 100 mg. of 

 aluminum phosphate present. The sol. is heated and, while hot, 5 gm. 



5 Mixer and DuBois : Jonr. Amer. Chem. Soc, 1895, xvii, p. 405. 

 •5 Schmidt and Hoagland obtained their sol. for analysis by ashing the tissues 

 and then dissolving the residue. 



