DETECTION OF PHOSPHORUS COMPOUNDS. 59 



tube free from the blue precipitate containing a slight blue pre- 

 cipitate which subsided after several hours leaving a brownish 

 supernatant fluid. Thus, the possible error in determining the 

 proportion of nitric acid necessary to prevent the blue reaction is 

 considerable, although the results are accurate enough for the 

 purposes of this investigation, as subsequent statements will show. 



REACTIONS OF SOLUBLE MOLYBDIC ACID WITH PHENYL- 



HYDRAZIN HYDROCHLORIDE IN THE PRESENCE 



OF NITRIC ACID. 



Percentage of Phenyl- Percentage of Nitric 



Strength of Molybdic Acid hydrazin Hydro- Acid Necessary to Pre- 



in Fractions of Ncrmal. chloride. vent Blue Reaction. 



O.O2 O.I 1.38 



0.04 o.i 2.26 



0.06 o.i 2.94 



0.08 o.i 3.27 



REACTIONS OF SOLUTIONS OF AMMONIUM MOLYBDATE WITH 

 PHENYLHYDRAZIN HYDROCHLORIDE IN THE PRESENCE 



OF NITRIC ACID. 



Solutions of ammonium molybdate when treated with phenyl- 

 hydrazin hydrochloride give, as stated by Macallum, a brown 

 color, and a brown precipitate slowly forms in the solution. In 

 the presence of nitric acid, however, provided the latter does not 

 exceed a certain amount which varies with the concentration of 

 the molybdate, the reaction consists in the production first of a 

 blue color and finally of a deep blue precipitate. If the amount 

 of nitric acid exceeds this maximum no reaction occurs at first, 

 but a brown color slowly develops in the solution. The follow- 

 ing table gives the concentration of nitric acid necessary to pre- 

 vent wholly the blue reaction with several concentrations of 

 molybdate. 



Percentage of Ammonium Percentage of Phenylhydrazin Per Cent. Nitric Necessary to 



Molybdate. Hydrochlotide. Prevent Blue Reaction. 



0.5 o.i 3.14 



I.O O.I 4.40 



1.5 o.i 5.03 



2.0 O.I 5.66 



