444 New Experiments on some of 
vised for ascertaining the composition of phosphoric acid. In this 
instance no phosphorous acid, as | ascertained by direct trials, 
is formed form the vapour ; and no substances are concerned ex- 
cept those that actually combine. M. Dulong’s method of as- 
certainining the composition of phosphoric acid, appears to me 
much too complicated to afford any results approaching tu ac- 
curacy. He first combines copper wire with phosphorus, by 
passing phosphorus over it by means of a stream of hydrogen 
gas; he then dissolves his phosphuret of copper in nitric acid, 
and determines the quantity of phosphoric acid formed by pre- 
cipitation : in all of which processes sources of error-may exist. 
M. Berzelius’s methods of ascertaining the composition of 
phosphoric acid, that of reviving gold from its oxide by means of 
phosphorus, and that of determining the quantities of phosphate 
and muriate of silver formed from perphosphorane, or the per- 
chloride of phosphorus, appear to me still more exceptionable ; 
yet his results on the quantity of oxygen approach nearer to mine 
than those of M. Dulong. 
The facts which | endeavoured to establish respecting chlorine, 
in a paper published in the Philosophical Transactions for 1810, 
show that the proportional or equivalent volume in which chlo- 
rine combines, is to that in which oxygen combines, as 2 to 15- 
and it follows, that 10 grains of phosphorus in forming the white 
sublimate, or perchloride, ought to combine with between 76 and 
80 cubical inches of chlorine. 
In experiments that I formerly made on this subject, by ad- 
mitting chlorine to phosphorus in exhausted vessels, and asver- 
taining the absorption by introducing solution of chlorine, I over- 
rated the absorption. I did not at that time know, what I have 
since ascertained, that a solution of chlorine in water, apparently 
saturated with chlorine, by agitation with it in long narrow vessels, 
will still take up more, by exposure to a great surface of chlorine 
in larger vessels. Under all circumstances, it is difficult to gain 
very precise results in experiments on the action of phosphorus 
on chlorine. Mercury acts so rapidly upon chlorine, that it can- 
not be employed in experiments in which the absorption i is to be 
determined. When common water is used, some of the gas is 
absorbed by the water, and, the sublimate being a very volatile 
substance, its vapour always i increases the volume of the residual 
gas. Some aqueous vapour likewise, in experiments over water, 
enters with the gas, which forms a volatile hydrate, the effect of 
which is likewise to diminish the apparent absorption of chlo- 
rine. 
I have always found the absorption greatest, when I have ope- 
rated in small retorts, connected by small stop-cocks with the 
vessel containing the chlorine, over water, Making the proper 
corrections 
