1819.} Philosophical Transactions for 1818, Part II. 211 
Considerable pains have been taken of late years to ascertain 
exactly the composition of the different compounds of phos- 
phorus ; but the subject is attended with so much difficulty, 
that even the repeated labours of the most eminent chemists of 
the present day have not been sufficient to elucidate it completely, 
or to produce full conviction in the minds of those who are prac- 
tically aware of the difficulties attending these kinds of investiga- 
tions. Sir H. Davy, whose sagacity and persevering industry 
place him in the very highest rank of the most eminent chemists 
that Europe can at present boast of possessing, may be said to 
have begun the investigation. In a former paper, he made us 
acquainted with several new compounds of phosphorus, which 
had not been recognized before, and rectified the notions of 
chemists about some of the other compounds of phosphorus, 
which had been previously discovered by Gay-Lussac and The- 
nard. In his System of Chemistry, he gives us the results of 
some other experiments; and among others, coincides with 
Lavoisier, respecting the composition of phosphoric acid, which 
he considers as a compound of about 1 phosphorus and 1:5 oxy- 
gen. Some time after, a paper on the composition of phosphoric 
acid and the phosphates was given to the world by Berzelius. 
This paper contained the results of a vast number of experiments, 
which had occupied the undivided attention of that most indefa- 
tigable chemist for several months. About the same period, an 
abstract of a paper by M. Dulong on the same subject appeared. 
The paper itself was afterwards published at full length in the 
third volume of the Memoires d’Arcueil. It contained the dis- 
covery of a new acid of phosphorus, to which Dulong gave the 
name of hypophosphorous acid. It is scarcely necessary to 
mention my paper on phosphuretted hydrogen gas, published in 
a preceding volume of the Annals of Philosophy. 1t appears to 
me to furnish a simpler and more unexceptionable method of 
determining the composition of the phosphoric and phosphorous 
acids than any other, and the method that must ultimately decide 
the question. 
The experiments of Berzelius and Dulong differing widely from 
the former estimates of Davy, he was induced to take up the subject 
a second time ; and the present paper contains the results of his 
new investigations. After various unsuccessful trials, he found 
that by putting phosphorus in a glass tube with a narrow mouth, 
he was enabled, by heating it ima retort filled with oxygen gas, 
to burn about 10 gr. of it in that elastic fluid, and ascertain the 
oxygen gas absorbed. From several experiments made in this 
way, in which from 6 to 10 gr. of phosphorus were burned, he 
concludes that phosphoric acid is composed of 100 phosphorus 
+ 135 oxygen. From other experiments related in this paper, 
Sir H. Davy considers himself entitled to conclude, that phos- 
a acid contains half the oxygen contained in phosphoric 
acid, : 
Let us compare these experiments of Davy with the concln- 
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