the compounds of chromium. 167 
copper) were dissolved in water ; and it was found that when 
this liquid was mixed with a solution of 29-75 grains of the 
crystals the whole copper was thrown down, and no residual 
sulphur remained in the liquid ; for no effect whatever was 
produced by adding to it a few drops of the solution of sul- 
phate of copper. Now, when sulphate of copper and a 
hydrosulphuret are mixed in the atomic proportions, the 
precipitate consists of bisulphuret of copper, composed of 
equal weights of sulphur and copper. But the copper in 
31*25 grains of sulphate of copper is eight grains. Conse- 
quently, 29*75 grains of the crystals contain just 8 grains of 
sulphur ; or, which is the same thing, 14*875 grains of the 
crystals contain 4 grains of sulphur. 
As 50 grains of the crystals gave 13*49 grains of soda, it 
is obvious that 14*875 grains must contain 4-013 grains, which 
differs by only ^th per cent from 4. 
The salt being in regular crystals, and not altered by ex- 
posure to the air, the water contained in it must be a deter- 
minate number of atoms. Now, 50 grains of the crystals 
gave 25-4 grains of liquid ; consequently, 14-875 grains 
would give 7*556 grains. But this liquid contained more than 
half a grain of saline matter : so that the quantity of water 
contained in 14*875 grains of the crystals does not amount to 
quite so much as 7 grains. If we suppose the water of the 
salt to be six atoms, its weight in 14-875 grains of the salt 
will be 6-75 grains. It is obvious from the experiment that 
it is not less than this, nor can it be more ; for 7 atoms of 
water would be 7*875, which was above the whole weight 
of the liquid obtained, and yet above half a grain of the 
weight found was owing to saline matter. 
