7 3 
Mr. Davy’s Experiments on 
would appear, that if potassium in forming a combination with 
this substance sets free hydrogene, it will be nearly the same 
quantity as it would cause to be evolved from water. And if 
the analysis of Mr. Proust and Mr. Hatchett, of the sul- 
phuret of iron, be made a basis of calculation, iron, in attract- 
ing sulphur from sulphuretted hydrogene, will liberate the 
same proportion of hydrogene as during its solution in diluted 
sulphuric acid; and taking Mr. Dalton’s law of proportion, 
the case will be similar with respect to other metals : and if 
such reasoning were to be adopted, as that metals are 
proved to be compounds of hydrogene, because in acting upon 
different combinations containing hydrogene, they produce 
the evolution of equal proportions of this gas, then it might 
be proved that almost any kind of matter is contained in any 
other. The same quantity of potash, in acting upon either mu- 
riate, sulphate, or nitrate of magnesia, will precipitate equal 
quantities of magnesia ; but it would be absurd to infer from 
this, that potash contained magnesia, as one of its elements ; 
the power of repelling one kind of matter, and of attracting 
another kind, must be equally definite, and governed by the 
same circumstances. 
Potassium, sodium, iron, mercury, and all metals that I have 
experimented upon, in acting upon muriatic acid gas, evolve 
dark coloured, and the arsenic appeared as a brown powder, both were probably hy« 
drurets ; this is confirmed likewise by the action of potassium upon arseniuretted, and 
phosphuretted hydrogene ; when the metal is in smaller quantity than is sufficient to 
decompose the whole of the gasses, there is always an expansion of volume ; so that 
arseniuretted and phosphuretted hydrogene contain in equal volumes, more hydrogene 
than sulphuretted hydrogene, probably half as much more, or twice as much more. 
From some experiments made on the weights of phosphuretted and arseniuretted hy- 
drogene, it would appear, that ioo cubic inches of the first weigh about io grains, 
a£ the mean temperature and pressure, and too of the second about 15 grains. 
