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the cause of these phenomena, because therein we have 
Osmosis accompanied by peculiar chemical decompositions. 
I have found that without any intervening membrane, similar 
phenomena can be produced. If a crystal of Copper Sulphate 
be placed in a test tube or flask, and the vessel be then filled 
with a solution of Potassium Sulphide of the proper strength, 
the formation of a black crust of Copper Sulphide, will be 
first observed upon the surface of the crystal. As soon as 
this is formed an ascending yellow current may be noticed, 
doubtless due to the formation of Potassium Bisulphide, If 
the solution of Sulphide be too dilute, it works too quickly ; 
while on the other hand a concentrated solution works im- 
perfectly, retarding the osmotic action considerably. If after 
about twelve hours the liquid be removed, and the black 
lump washed with care and then broken open, we find 
metallic Copper in the interior, no part of the original crystal 
being left undecomposed. Here we have a clear case where 
the deposit of Copper Sulphide takes the place of a membrane. 
That this deposit must possess a peculiar molecular arrange- 
ment to yield the result described, can be demonstrated at 
once if we repeat the experiment with a crystal of Silver 
Nitrate. The first step here also, is the turning of the surface 
of the crystal into a black crust of Sul phide, but we look in 
vain for the ascending yellow current. Neither do we find a 
similar result in the interior of the black lump if we cut it 
open. We find the central portion almost unchanged, only 
a small amount of metallic Silver being formed. The action 
of Potassium Sulphhydrate is very different, producing a 
violent and perfect decomposition of the crystal of Silver 
Nitrate, the rising bubbles of Sulphuretted Hydrogen gas do 
not permit of the formation of a crust, 
Similar differences we find on pouring Caustic Potash over 
both salts; the copper salt will yield a loose mixture of black 
Oxide and blue Hydrate, and the decomposition is complete, 
while with Silver Nitrate we find under the thin layer of 
Oxide, the original salt undecomposed. | 
As regards the molecular structure of the crusts, of metallic 
Sulphides, it is evident that the crust of the copper salt must 
poocs LYC. NAT. Hist., N) Y.—Vor, 1 19 
