1819.] Philosophical Transactions for 1818, Part II. 213 
were conducted in quite a different way from mine, this very 
near comcidence induces me to rely upon the results as approach- 
ing the truth very nearly. My method was much more suscep- 
tible of precision than Davy’s. The only part of my experiments 
in which an error was likely to arise was, in taking the specific 
gravity of the phosphuretted hydrogen gas; but I do not think 
the error in that process could be considerable. Iam disposed, 
therefore, to consider the results contained in my paper on phos- 
phuretted hydrogen gas as exhibiting the accurate composition 
of phosphorous and phosphoric acids. 
Soon after the publication of this paper of mine, Dulong’s 
discovery of a new acid of phosphorus, to which he gave the 
name GF hiyniohoiphnow acid, became known. ‘This acid con- 
tained less oxygen than phosphorous acid. Soon after also, Mr. 
Dalton, in a paper on phosphuretted hydrogen gas, announced 
that one volume of it combined with two volumes of oxygen gas. 
As I was quite sure of the accuracy of my previous proportions, 
I was led to infer, that a volume of phosphorus is capable of 
combining with 0-5, 1, and 1-5 volumes of oxygen, or, which is 
the same thing, 1 atom of phosphorus with I atom, 2 atoms, 
and 3 atoms of oxygen. The most obvious way of accounting 
for this was to consider the two acids which Thad formed as 
hypophosphorous and phosphorous acids, and to make the new 
acid of Dalton, the phosphoric acid. This accordingly was the 
conclusion that I drew in the last edition of my System of 
Chemistry. 
But the new experiments of Davy related in this paper, induce 
me to revert back again to my original statement ; for I think it 
hardly possible that two sets of experiments, so different from 
each other as Davy’s and mine, could have accorded so nearly 
as they do, if they were inaccurate. 
I must presume, therefore, that Mr. Dalton’s result, which I 
have been myself unable to verify, is either inaccurate, or that he 
has formed an acid containing more oxygen than the phosphoric. 
Dulong’s hypophosphorous acid is probably a compound of 
two atoms of phosphorus and one atom of oxygen. On that 
supposition, it will consist of 
Phosphorus ~..0. ses viene 100-0 
ORY SOs ileidditee alts Sale de'd 33°3 
numbers which approach fully as nearly to Dulong’s analysis as 
could be expected, considering the imperfection of the mode 
which he employed. 
These new experiments of Sir H. Davy then possess consider- 
able value. They verify mine, and seem to leave little doubt 
about the weight of an atom of phosphorus, and the composition 
of phosphorous and phosphoric acids. But the constitution of 
phosphoric acid, as it results from the experiments of Davy and 
my own, does not agree with the constitution of it as resulting 
