96 



oxygen in the phosphorous acid to be to that in the phosphoric as 

 3 to 5. 



After showing that the only possible source of error in his former ex- 

 periments was the smallness of the quantity of the phosphorus burned, 

 Sir Humphry describes various modes of effectually carrying on the 

 combustion upon a larger scale, and gives the preference to that in 

 which the vapour of phosphorus, passing from the orifice of a small 

 tube, is made to burn in a retort filled with pure oxygen. The 

 mean result of several experiments carefully conducted upon this 

 plan, gave the composition of phosphoric acid at 100 phosphorus + 

 134-5 oxygen. 



The author having shown the insufficiency of Dulong's method for 

 ascertaining the composition of phosphoric acid and of the chlorides 

 of phosphorus, proceeds to detail his researches upon the latter com- 

 pounds, and upon the constitution of phosphorous acid. The result 

 of several experiments indicated the composition of perchloride of 

 phosphorus to be I'OO of phosphorus + 6 of chlorine ; and showed 

 that phosphorous acid contained half the quantity of oxygen existing 

 in the phosphoric acid, and the liquid chloride half the quantity of 

 chlorine contained in the solid perchloride. These experiments suf- 

 ficiently agree with each other to afford the means of determining 

 the equivalent number of phosphorus. Thus, if phosphoric acid be 

 supposed to consist of two proportions of oxygen and one of phos- 

 phorus, the number representing the proportion in which phospho- 

 rus combines will be 22'3. If the absorption of chlorine in forming 

 phosphorane be made the datum, the number will be 22'2. If the 

 quantity of horn silver formed from the liquid chloride be assumed 

 as the datum, the number will then be 23 '5. The mean of all is 

 22'6, or the double 45'2, from which, if we take away the decimal, 

 we obtain 45. The author's experiments upon phosphate of potash 

 also agree with this number. 



The next subject discussed in this paper is the hypophosphorous 

 acid of M. Dulong. Although Sir Humphry has satisfied himself of 

 the existence of this acid, he is not disposed to regard the methods 

 of analysis adopted by its discoverer as satisfactory. When hypo- 

 phosphite of baryta is decomposed by heat, it is converted into phos- 

 phate of baryta and hydrophosphoric gas ; and knowing the quan- 

 tity of acid in the former, and of phosphorus in the latter, it is easy 

 in this way to learn the composition of the hydrophosphorous acid. 

 The results of Sir Humphry's experiments, however, lead to the con- 

 clusions adopted by Dulong ; namely, that the quantity of oxygen in 

 the hydrophosphorous acid is half that which is contained in the 

 phosphorous acid. M. Dulong has suggested that the acid described 

 by the author as a mixture of phosphorous and phosphoric acids, is 

 a peculiar chemical compound, and proposes to call it phosphatic 

 acid ; but as it has no crystalline form, nor any marked characters ; 

 as it is not of uniform composition ; and as phosphorous and phos- 

 phoric acids mixed, produce a substance of the same kind, Sir Hum- 



