S52 M. Berzelius on some Compounds 
I have long suspected that the result of my experiments con- 
cerning the composition of oxide of zinc, indicates a small ex- 
cess of oxygen, occasioned by the presence of iron in the distil- 
led zinc which I employed. My suspicion acquires force from 
this analysis, which (supposing the substance operated upon 
equally pure in all cases), it is easy to perform with an accuracy 
that shall prevent any variation in the first decimal place of the 
number which expresses the weight, especially of the oxygen. 
For determining this point, I made several new attempts to ob- 
tain zinc absolutely pure, but the recurrence of my former diffi- 
culties prevented me from continuing them. 
It may be objected to our opinion concerning the nature of 
the substance now analysed, that the hydrate contains more 
water than when it occurs in an isolated state ; but we have al- 
ready seen, that in double salts the quantity of water may be 
different from what exists in the ingredients, taken separately. 
In an excellent work, published fifteen years ago, upon the 
composition of the different ores of zinc, which are named cala- 
mines, Mr Smithson, besides the crystallised neutral dry carbo- 
nate of zinc, examined another species of earthy carbonate of 
zinc from Carinthia, and found it to be composed of 71.66 per 
cent, of oxide of zinc, 13.34 of carbonic acid, and 15 of water. 
Its composition is evidently the same as that of the artificial sub- 
stance which we have just analysed. Mr Smithson himself con- 
sidered this substance as a chemical combination of the carbonate 
and the hydrate of zinc ; and the inaccuracy of the proportions 
which he assigns to these ingredients must have proceeded 
from his unacquaintance with those laws of combination whicli 
have since been discovered. 
Subsulphate and Submuriate of Magnesia . — Before finishing 
this paper, I shall say a few words of those precipitates which 
are produced by caustic ammonia, in the solutions of sulphate 
and muriate of magnesia. It has often been maintained that 
these precipitates happen, from the tendency which salts of am- 
monia and magnesia have to form double salts. Mr Pfaff of 
Kiel even thought it in his power to determine the composition 
of these double salts, from tlie quantity of precipitate, obtained ^ 
by mixing a magnesian salt with caustic ammonia. But this 
supposition is incorrect ; for I have ascertained that the preci- 
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