54 R- R- BENSLEY. 



binations by the reagent, converted into orthophosphoric acid and 

 immediately precipitated in situ as ammonium phosphomolyb- 

 date. As a result of the experiments, however, I have been 

 forced to the conclusion that the whole of the reaction obtained 

 by Macallum's method is due to compounds of molybdenum 

 other than phosphomolybdate and that the phosphorus of the 

 tissues is not concerned in the production of the reaction at all. 

 For the purpose of testing the reactions of molybdic acid with 

 phenylhydrazin hydrochloride, I prepared two soluble molybdic 

 acids. The first of these was prepared by the method recom- 

 mended by Ullik ('67). Barium molybdate, prepared by pre- 

 cipitating a warm solution of ammonium molybdate with barium 

 chloride washing thoroughly with hot distilled water, and dry- 

 ing the precipitate on a water bath at 100 C., was suspended 

 in water and decomposed with its equivalent of sulphuric acid. 

 The solution was then filtered, tested for barium, sulphuric acid 

 and chlorides, from which it was found to be free, and the total 

 acidity was determined by titration with a normal solution of 

 sodium hydroxide, using phenolphthalein as indicator. Assum- 

 ing that the solutions contained a molybdic acid having the for- 

 mula H 2 Mo 2 O 7 the concentration of the solutions obtained by the 

 method described above was in the case of one preparation 5.25 

 per cent., in another 7.52 per cent. The second molybdic acid 

 was colloidal molybdic acid prepared by the process recommended 

 by Graham (64), except that ammonium molybdate was employed 

 instead of sodium molybdate. A solution of ammonium molyb- 

 date in hydrochloric acid was dialyzed for several days against 

 distilled water, until free from chloride. The resulting solution 

 was then titrated against normal soda solution using phenolphtha- 

 lein as indicator. According to Sabanejew ('90) the molecular 

 weight of the molybdic acid prepared by Graham's method as 

 determined by lowering of freezing point is 620 corresponding to 

 the formula H 2 Mo 4 O 13 . Assuming that the same compound was 

 obtained by the dialysis of the solution of ammonium molyb- 

 date in hydrochloric acid the solution obtained contained 6.73 

 per cent, of colloidal molybdic acid. From these solutions were 

 prepared the various solutions mentioned in the succeeding ex- 

 periments. 



