5O R. K. BENSLEY. 



not surprising that the results of Lilienfeld and Monti have been 

 subjected to careful experimental examination by a number of 

 other investigators. 



Raciborski ('93) in 1893, in his review of Lilienfeld and Monti's 

 article, showed that the reaction of ammonium phosphomolybdate 

 with pyrogallic acid resulted in the production of a green com- 

 pound, while ammonium molybdate gave by reduction with the 

 same reagent a brown compound. He concluded that the brown 

 reaction of Lilienfeld and Monti was due to ammonium molyb- 

 date mechanically imbibed by the section, and not to ammonium 

 phosphomolybdate. 



Heine ('96), also, showed that phosphorus-free histone, pre- 

 pared from the thytnus, formed with the nitric-molybdate reagent 

 compounds from which the ammonium molybdate could not be 

 removed by washing in water, and in which it could be detected 

 by the use of reducing compounds. For this purpose he em- 

 ployed stannous chloride. 



Macallum confirmed Raciborski's observations as to the color 

 compounds produced by the reduction of ammonium phospho- 

 molybdate and ammonium molybdate respectively, and showed 

 that ammonium molybdate could not be removed from tissues 

 which had been treated with the nitric-molybdate reagent even 

 by washing for several months in changes of distilled water. 

 Macallum perceived the necessity of substituting for pyrogallic 

 acid, which gives colored compounds with both the phospho- 

 molybdate and the molybdate of ammonium, some reagent which 

 would discriminate between these two compounds, and give a 

 color reaction with phosphomolybdate alone. This condition he 

 found to be fulfilled by zinc chloride, previously introduced for 

 this purpose by Polacci ('94), which gave a green color with the 

 phosphomolybdate but did not act on ammonium molybdate. 

 Owing, however, to the fact that zinc chloride acted very slowly, 

 he finally adopted as a reducing agent phenylhydrazin hydro- 

 chloride, which, according to him, made a very marked distinc- 

 tion, in the absence of alcohol or of caustic alkali, between the 

 molybdate and the phosphomolybdate compounds. It gave with 

 the former in powder the brown oxide at once, in solution, a 

 brownish precipitate, which appeared at once, or later, according 



