On definite Proportions. 43 
tie acid contains such a quantity of water as is sufficient for oxi- 
dating with its oxygen as much metal as is capable of producing 
a neutral salt with the dry muriatic acid; and Gay-Lussac has 
proved the same thing in his excellent essay on the combinations 
of the gases. I had also found by experiment that the sulphuric 
acid could only be concentrated by boiling, until the remaining 
water contained one-third as much oxygen as the acid, that is, 
as much as would be required by the same acid in a base capable 
of saturating it. I had assumed the component parts of water 
113 of hydrogen, and 88} of oxygen, from my own experiments, 
confirmed by those of Biot and Arago. Mr. Gay-Lussac makes 
them 13} and 863, without altering the determination of the 
specific gravity of the gases. I shall endeavour to throw a clearer 
light on these combinations of water by the experiments now to 
be described. [ ought perhaps to have been deterred from mak- 
ing some of them public by the difficulty of the subject, and the 
impossibility of fully establishimg my opinions respecting the com- 
position of hydrogen ; but science would often have profited by 
_ communications which have been withheld by too great a desire 
of minute accuracy. ; 
I shall here make some preliminary remarks on subjects con- 
nected with the immediate objects of my pursuit; and first, re- 
specting the impossibility of exhibiting some of the acids in a 
separate state. We have learned from the excellent experiments 
of MM. Gay-Lussac and Thenard, that the muriatic acid can- 
not be separated from the substances with which it is combined, 
unless in the presence of water, with which it may combine at 
the moment of its formation. Mr. Davy’s inferences from this 
fact are well known; but we shall here pause alittle to examine 
the affections of other acids in similar circumstances. 
Sulphur, as we have reason to believe, is capable of four de- 
grees of oxygenization. ‘The first and second are unknown ex- 
cept in combination with the muriatic acid ; the third is the sul- 
phurous acid, and the fourth the sulphuric. No themist has 
ever obtained dry sulphuric acid, and whoever attempts to pro- 
cure it, will find sulphurous acid in its place. If, for example, 
we burn sulphur in perfectly dry oxygen, a very slight trace only 
of sulphuric acid is formed, and this originates from the hydrogen 
present in the sulphur, which affords a little water. If we dry 
sulphate of the oxide of iron, or alum, with proper care, and 
_ attempt to drive off the sulphuric acid by heat, we obtain oxy- 
gen and sulphurous acid, without the condensation of a trace of 
sulphuric acid; but if we cause aqueous vapour to pass over 
these salts when heated, we immediately obtain sulphuric acid 
condensed in the receiver. It is known on the other hand, that, 
if we throw sulphuretted muriatic acid into water, sulphurous acid 
18 
