144 ABSORPTION OF SALINE SUBSTANCES BY CHARCOAL. 
solved in S grms. of acid diluted with water 2 grms. of ox- 
ide of copper obtained by calcining the nitrate, evaporated 
the solution to dryness, then redissolved the salt in 100 
grms of distilled water, and placed the solution in a wide 
mouthed bottle with a ground stopper. I then poured some 
ammonia into it until the precipitate which formed at first 
had redissolved, and the liquid had become perfectly clear ; 
the bottle was finally filled with boiled distilled water, and 
a bright slip of copper, the weight of which was known, in- 
serted. In the course of five days the experiment wascom- 
pleted, and the solution had become perfectly colorless ; 
the slip of copper was then removed, washed, wiped dry 
with care and weighed. It had lost i of its weight. The 
expeiiment, repeated several times in the same manner, 
furnished the same result. 
As the oxide of copper contains precisely half the quan- 
tity of copper contained in the subtoxide, it proved that my 
primitive solution contained i copper. If, therefore, after 
having been filtered through charcoal, it contained less 
copper, that must have held it back. A solution of copper 
was therefore prepared like the preceding, and transferred 
into the displacement apparatus with JO grms. of animal 
charcoal. As soon as the operation was finished, I washed 
the charcoal with a little distilled water, added this wash- 
water to the filtered liquid, supersaturated it with ammonia, 
&c. As soon as the decoloration was complete, I removed 
the s'ip of copper to weigh it. It had lost only 0-75 of its 
weight ; the charcoal had therefore retained 0-65 copper, 
or nearly half of what the solution contained. I repeated 
the experiment, and obtained 70, and a third time 0*75. 
With regard to the alkaline sulphates, they always ap- 
peared to be absorbed in very minute proportions; for I 
was not on'y able to detect their presence readily by means 
of reagents, but sometimes even from the bitter taste of the 
solution, especially when the liquid had been slightly con- 
centrated. 
