96 
DR. ANDREWS ON THE HEAT DISENGAGED 
Formiate of Copper and Zinc . — The solution of this salt corresponded in all re- 
spects with that of the sulphate of copper. 
I. Air 17°’8. Increment found 2°‘43, corrected 2°-36. 
II. Air 17°'6. Increment found 2°'41, corrected 2° 34. 
I. II. Mean. 
873° 865° 869°. 
Collecting the foregoing results, we find for the heat of combination from the first 
series, ^ 
Sulphate of copper 864 
Chloride of copper 857 
Acetate of copper 838 
And from the second series. 
Sulphate of copper 868 
Chloride of copper 860 
Acetate of copper 877 
Formiate of copper .... 869 
The agreement among these numbers is as close as can be expected in experiments 
of this kind, in which other disturbing sources of heat are present, whose precise in- 
fluence it is difficult to estimate. It is very plain that the heat developed is wholly 
independent of the acid with which the metal is combined. The results obtained in 
the two series, in which solutions of very different strengths were employed, differ 
little from one another, but an accurate comparison cannot be made, as no correction 
for the disturbing thermal effects was applied to the numbers of the first series. We 
may, however, conclude that, within the limits of these experiments, the heat deve- 
loped by the same amount of metallic substitution is nearly the same in solutions of 
different strengths. It is probable that this observation will not be found strictly to 
apply to very concentrated solutions. 
It is almost unnecessary to remark that if, in the course of the reaction, any 
chemical change occurs besides the displacement of one metal by another, the heat 
evolved will no longer be the same. On this account, solutions of the metallic nitrates, 
especially if concentrated, are not adapted for this investigation. 
If we take the mean of the numbers in the second series, and adopt 3'96 as the atomic 
weight of copper, we shall have for the heat extricated during the displacement of 
C. F. 
1 grm. copper by zinc .... 868° or 1562° 
1 equiv. copper by zinc .... 3435° or 6183°. 
Salts of Copper with Iron. 
Two distinct series of experiments similar to the preceding were made on the pre- 
cipitation of the salts of copper by iron. In the first series, the apparatus and solu- 
tions were in all respects the same as in the experiments with zinc. A large quantity 
(from 12 to 13 grms.) of the precipitating metal was required. 
