58 R. R. BENSLEY. 



constant for a given concentration of the other two constituents 

 but varied directly with the concentration. This fact made it 

 necessary to determine the conditions of this reaction with 

 ammonium molybdate if solutions of the hydrochloride con- 

 taining nitric acid were to be used for the reduction of the sec- 

 tions, because in trying to eliminate the reduction of the molybdic 

 acid by using a solution of the hydrochloride containing nitric 

 acid, a new source of error might be introduced, inasmuch as the 

 nitric acid would make ammonium molybdate available to the 

 blue reduction. 



The experiments to determine the limits of these reactions 

 were made in test-tubes in much the same way as experiments 

 in haemolysis are carried out. In each of a series of test-tubes 

 was placed, from a pipette graduated in fiftieths of a cubic centi- 

 meter, a measured quantity of the solution of molybdic acid. 

 To this was added a quantity of nitric acid solution of known 

 strength increasing by increments of one tenth of a cubic centi- 

 meter from tube to tube. Sufficient distilled water was then 

 added to make the contents of each tube up to 9. 5 c.c., and finally 

 0.5 c.c. of a two per cent, solution of phenylhydrazin hydro- 

 chloride was added to each tube. In such a series of tubes, if a 

 sufficient range of concentrations of the nitric acid was included 

 the tubes at one end of the series would give the blue reduction, 

 those at the other would at first show no signs of reaction, but 

 after several hours would develop a brownish color. At some 

 point in the series two tubes, side by side, differing from one 

 another only in the nitric acid content, would present the one a 

 blue, the other a brown color. When solutions of nitric acid 

 containing 32 grammes of nitric acid per looc.c. were employed, 

 that is, when the difference in the contents of two tubes amounted 

 to .032 gr. of nitric acid, the contrast in color between the tubes 

 which marked the limit of the reaction was a very striking one. 

 Attempts to define this limit more accurately by the use of more 

 dilute solutions of nitric acid, and accordingly smaller increments, 

 of nitric acid from tube to tube did not result more satisfactorily. 

 For example in a series of tubes in which the increment of nitric 

 acid was 0.012 gr. from tube to tube, the transition was distrib- 

 uted over several tubes, those immediately preceding the first 



