DETECTION OF PHOSPHORUS COMPOUNDS. 57 



obtained by the procedure of Macallum was due to absorption of 

 tnolybdic acid from the nitric molybdate solution. There was, 

 however, some possibility that even this reaction with molybdic 

 acid solutions depended on the presence of phosphorus and its 

 liberation as phosphoric acid. It might be supposed that this 

 phosphoric acid reacted with the molybdic acid to produce 

 phosphomolybdic acid which was in turn precipitated by the 

 albumens of the tissues. Or it might even be supposed that 

 ammonium phosphomolybdate was formed, the ammonium ions 

 necessary to the reaction being furnished by the albumens. That 

 this is not the case, and that the reaction obtained by the use of 

 molybdic acid solutions is in no way dependent on the phosphorus 

 content of the tissue, I think the following experiments will 

 show. 



In studying the reaction of solutions of molybdic acid with 

 phenylhydrazin hydrochloride, I found that the addition of nitric 

 acid to the mixture retarded the reaction and if a sufficient quan- 

 tity were present prevented it altogether. Accordingly, experi- 

 ments were undertaken to determine the limits of this reaction 

 with molybdic acid, ammonium molybdate, and ammonium 

 phosphomolybdate, respectively, in the hope that a sufficient dif- 

 ference in the behavior of these compounds would be discovered 

 to enable one to employ a solution of phenylhydrazin hydro- 

 chloride containing enough nitric acid to inhibit the reduction of 

 molybdic acid and of ammonium molybdate while permitting the 

 reduction of ammonium phosphomolybdate, and thus discrim- 

 inate between these compounds occurring in tissues treated by 

 Macallum's methods. 



I found that with a constant concentration of phenylhydrazin 

 hydrochloride, the amount of nitric acid required to prevent the 

 reduction to the blue oxide of molybdenum varied directly with 

 the concentration of the molybdic acid but was constant for any 

 given concentration. 



I found, moreover, that the blue reduction was invariably 

 obtained in solutions of ammonium molybdate containing nitric 

 acid, when they were treated with solutions of phenylhydrazin 

 hydrochloride, provided the amount of nitric acid did not exceed 

 a certain amount, which, as in the case of molybdic acid, was 



