540 
MR. T. J. BAKER ON THE THERMO-CHEMISTRY 
The numbers in the last column have been plotted as ordinates against percentages 
of copper as abscissm, and will be discussed later. 
Although the results arrived at appeared very satisfactory, it was considered 
advisable to confirm them by using another solvent, and a mixture of ammonium 
chloride and cupric chloride solutions was chosen. 
Series III.— Mixed Ammoxium Chloride axd Cupric Chloride Solutioxs 
AS SOLVEXT. 
Each litre of solution contained 1 gramme-molecule of cupric chloride and 2 
o'ramme-molecules of ammonium chloride. 
O 
Copper is converted into cuprous cldoride by this solution at the expense of the 
cupric salt, which suiters reduction to the cuprous condition. 
The ammonium chloride serves, by its solvent action, to keep the surface of the 
metallic particles free from this cuprous chloride, v'hich would otherwise delay 
dissolution. 
Zinc placed in the solution precipitates finely divided copper from the cupric 
chloride, and this copper is rapidly re-dissolved, as explained above. 
The solution was found to dissolve the alloys rapidly unless the percentage of 
copper was greater than 60, and, owing to this circumstance, the experiments were 
not continued beyond the alloy containing 62'2 jjer cent, of cojiper. 
This difficulty arose from the fact that it was impossible to obtain those alloys 
which are rich in copper in a sufficiently comminuted state. 
Specific Heat of the Solution. 
This was found in a manner similar to that previously described. 
In three successive experiments the following values were obtained :— 
(i.) -8102 (ii.) -8102 (hi.) -812. 
Mean value = '8108. 
In tlie experiments which follow, the calorimeter always contained 520 grammes 
of the solution, and the water equivalent was 
(520 X ’8108) -h 16 = 437'6 grammes. 
Experience sliowed that it was usually necessary to moisten the metallic powders 
with rather more water than when ferric chloride was the solvent, or the rate of 
dissolution was apt to be slow. 
In the following Tallies the weight of water used for this ])urpose has been added 
to the water equivalent given above. 
Heat of Dissolution of Copper in Ammonium Cupric Chloride Solution. 
The heat evolution in this reaction was so small that exceptionally large quantities 
of copper had to he employed. This necessitated the addition of some 3 grammes of 
water to the copper powder to bring it into a suitahle condition for rapid dissolution. 
