410 Sir H. Davy on some Combinations 
tual decomposition of water, and the phosphoric compounds 
of chlorine are merely the phosphoric acid from the sublimate 
and the phosphorous acid from the liquor, and muriatic acid 
gas ; so that the quantity of phosphorus being the same, it is 
evident that phosphoric acid must contain twice as much oxy- 
gene as phosphorous acid, which harmonizes with the results 
of the decomposition of hydrophosphorous acid. For supposing 
water to be composed of two proportions of hydrogene, and one 
of oxygene, and the number representing it 17 ; then 174 
parts of hydrophosphorous acid must consist of two proportions; 
34 parts of water, and four proportions of phosphorous acid, 
containing 80 of phosphorus and 60 of oxygene; and three 
proportions of phosphoric acid must be formed, containing three 
proportions of phosphorus 6 o, and six proportions of oxygene 
go, making 150. 
It is scarcely possible to imagine more perfect demonstrations 
of the laws of definite combination, than those furnished in the 
mutual action of water and the phosphoric compounds. No 
products are formed except the new combinations; neither oxy- 
gene, hydrogene, chlorine, nor phosphorus is disengaged, and 
therefore the ratio in which any two of them combine being 
known, the ratios in which the rest combine, in these cases, may 
be determined by calculation. 
I converted phosphorus into phosphoric acid, by burning it 
in a great excess of oxygene gas over mercury in a curved glass 
tube, and heated the product strongly. I found in several pro- 
cesses of this kind, that for every grain of phosphorus consumed, 
four cubical inches and a half of oxygene gas were absorbed ; 
which gives phosphoric acid as composed of 20 of phosphorus 
to 30.6 of oxygene ; a result as near as can be expected to the 
