of Phosphorus in Animal and Vegetable Tissues. 471 



chloride does this, but in an unsatisfactory way. It is very slow in 

 its action, and feeble in its reducing power. It gives a green reac- 

 tion with the phospho-molybdate compound, but none with the 

 molybdate in the presence of nitric acid. Stannous chloride reduces 

 both the compounds at once, forming the blue oxide of molybdenum, 

 and therefore it is, for the point in view, valueless. Ferrous sulphate 

 is also very slow in its action, and it has the disadvantage of giving* 

 a faint green colour to the tissue, independent of that which may be 

 produced in the phospho-molybdate compound. 



The reagent which I found the most valuable from every point of 

 view is phenylhydraziii hydrochloride. This, in an aqueous solu- 

 tion of 1 4 per cent, strength, is certain in its action if it is freshly 

 prepared or not more more than two or three days old. It, in the 

 absence of alcohol or of a caustic alkali, makes a very marked dis- 

 tinction between the molybdate and the phospho-molybdate com- 

 pounds. It gives with the former, in powder, the brown oxide at 

 once, in solution, a brownish precipitate which may or may not 

 appear immediately, depending on the strength of the solution, but 

 in a solution of the molybdate containing nitric acid, e.g., that used 

 as the reagent for phosphoric acid, it has no apparent effect on the 

 molybdenum compound, although, in a few minutes, a soluble, red- 

 dish, aromatic compound may be formed in the solution. On the 

 other hand, with phospho-molybdates, either in the presence or in 

 the absence of ammonium molybdate, or nitric acid, or of both, it 

 gives at once the dark-green oxide of molybdenum. Examined 

 under the microscope, the crystals of the phospho-molybdate alone 

 are found to have the green colour, which, after an hour's action of 

 the phenylhydrazin, is so dark as to suggest, at first sight, black. 

 That this reaction depends upon the presence of phosphoric acid, 

 may be clearly shown by adding to a mixture of the reducing 

 reagent and of the nitric molybdate solution a quantity of phos- 

 phoric acid solution. Although the mixture will stand for several 

 minutes without any change other than the formation of a slightly 

 reddish solution, yet on the addition of the acid solution the dark- 

 green reaction appears immediately and markedly, sometimes accom- 

 panied by the formation of a blue-violet soluble compound. No 

 other acid exercises a like effect. Solutions of potassium hydrate 

 and sodic hydrate and alcohol, in a certain proportion, will call forth 

 in the mixture a greenish- blue or blue colour, which, in the case of 

 the alcohol preparation, fades out in twenty-four hours. In this 

 latter, the colour would appear to be due to the formation of an 

 aromatic compound, and not directly to an alteration in the molyb- 

 date. Nitric acid alone will produce, in a solution of phenylhydr- 

 azin, a reddish colour, and rarely also, when ammonium molybdate is 

 present, a blue-violet colour, which appears to be due to a phenylic 



