DETECTION OF PHOSPHORUS COMPOUNDS. 63 



The facts on which the conclusion is based are, briefly, as 

 follows : 



The essential conditions of a successful phosphorus reaction 

 are, first, that the phosphorus may be liberated from its organic 

 combinations at a point short of the destruction of the recogniz- 

 able structure of the cell ; second, that the liberated phosphorus 

 be precipitated at once at the point of origin as ammonium phos- 

 phomolybdate ; third, that the reducing substance employed to 

 make the phosphomolybdate visible for microscopic study act on 

 phosphomolybdate and on no other compound of molybdenum 

 which may be present in the tissue. 



Phenylhydrazin hydrochloride does not meet the third condition 

 because it reduces to the blue oxide of molybdenum, soluble 

 molybdic acid in the test tube as well as molybdic acid combined 

 with the tissue constituents in sections. 



Phenylhydrazin hydrochloride also produces the blue oxide 

 when treated with ammonium molybdate in the presence of nitric 

 acid, provided that the latter does not exceed a certain concen- 

 tration which is constant for constant concentrations of the mo- 

 lybdate. 



Nitric acid affects the reduction of molybdic acid, ammonium 

 molybdate, and ammonium phosphomolybdate, by phenylhydra- 

 zin hydrochloride in the same way, namely, retards the reduc- 

 tion, but to different degrees, inasmuch as low concentrations of 

 nitric acid prevent the reduction of the two former to the blue 

 oxide, while high concentrations of nitric merely retard the blue 

 reduction of the phosphomolybdate. Accordingly, if phospho- 

 molybdate is formed at the site where a reaction is obtained by the 

 method of Macallum, the reaction ought to be elicited by treat- 

 ment of the sections with solutions of phenylhydrazin in having 

 a high content of nitric acid. This, however, the experiments 

 show is not the case. Even low concentrations of nitric acid 

 eliminate the greater portion of the reaction, and the reaction is 

 entirely abolished by a nitric acid content which has little effect 

 on the reduction of phosphomolybdate of ammonium artificially 

 introduced into sections for purposes of control. Furthermore, 

 the reaction is abolished at the same concentration of nitric acid 

 with sections treated with Macallum's nitric molybdate reagent 



