254 
Mr. Davy's Researches on 
Half a grain of potassium decomposes nearly three cubical 
inches of phosphuretted hydrogene, and sets free rather more 
than four cubical inches of hydrogene ; and the phosphuret 
formed seems to be of the same kind as that produced by 
direct combination of the metal with phosphorus. 
If, according to Mr. Dalton’s ideas of proportion, the 
quantity in which sulphur enters into its combinations were 
to be deduced from its union with potassium, in which it seems 
to form about ^ the weight of the compound, the number 
representing it would be 13.5. I have lately weighed sulphu- 
retted hydrogene, and sulphureous acid gas, with great care : 
the specific gravity of the first at mean temperature and 
pressure, from my experiments, is 10645, which differs very 
little from the estimation of Mr. Kirwan : that of sulphureous 
acid gas I find is 20967. Sulphuretted hydrogene, as I have 
shown, contains an equal volume of hydrogene ; and on this 
datum the number representing sulphur is 13.4. I have never 
been able to burn sulphur in oxygene without forming sul- 
phuric acid in small quantities ; but in several experiments I 
have obtained from 92 to 98 parts of sulphureous acid from 
100 of oxygene in volume ; from which I am inclined to 
believe, that sulphureous acid consists of sulphur dissolved in 
an equal volume of oxygene ; which would give the number 
as 13.7* nearly, considering the acid gas as containing 1 pro- 
* The estimation from the composition of sulphuretted hydrogene, must be consi- 
dered as most accurate, and that from the formation of the sulphuret of potassium as 
least accurate : for it was only by combining sulphur and potassium in small pro- 
portions, and ascertaining in what cases uncombined sulphur could be distilled from 
the compound, that I gained my conclusions concerning the composition of the sul- 
phuret of potassium. 
In the last Bakerian lecture, I have estimated the specific gravity of sulphuretted 
