which depeitd on weak Affinities. ^53 
pitate varies in quantity according to the quantity of ammonia ; 
by employing a very great excess of which, nearly all the mag^ 
nesia may be precipitated. The precipitates in question are not, 
however, pure hydrates of magnesia. That which we obtain 
from the sulphate is half translucent whilst it continues in the 
liquid ; it has a granular appearance, and deposites itself very 
quickly, as if it were heavy. That which results from the muriate 
is white, opaque, and mucous ; and it is very slowly deposited. 
In the first I found, magnesia, 67.5 per cent. ; sulphuric acid, 1.6| 
water, 30.9. The oxygen of the water somewhat exceeds that 
of the earth, wherefore that portion of magnesia which is com- 
bined with the sulphuric acid, must be joined to a greater pro- 
portion of water, than that other portion of magnesia which 
forms the base of the hydrate. Since this sulphuric acid cannot 
be extracted by water, it evidently belongs to the chemical 
Gotnposition of this substance. At present it is difiicult to 
make an analysis of this compound, sufficiently exact for being 
calculated with certainty, because one of the ingredients is found 
in^ such small quantity ; but the composition will probably be 
found to consist of one molecule of a subsulphate of magnesia 
with water of combination, and of a great number of molecules 
of hydrate of magnesia. The same is likely to be the case with 
the precipitate which results from the muriate of magnesia. It 
is very difficult to obtain this substance in a state of purity, be- 
cause its mucosity prevents the water from passing, and there- 
fore causes the salt, before it can be washed, to attract a very 
considerable quantity of carbonic acid. For this reason, I have 
not been able to analyse it accurately. I perceived, however, 
that there was about 1 per cent, of muriatic acid upon which 
the water had no influence. 
These researches indicate a species of combinations, which 
deserve to be examined with more attention than has hitherto 
been bestowed upon them. It is plain, that the affinities upon 
which they depend, must have performed an important part in 
forming the inorganic portion of our globe ; and that the study 
of them may become highly advantageous in our inquiries con- 
cerning the nature of mineral substances. 
VOL. I.' NO. 2. OCTOBER 1819. S 
