ACCOMPANYING BASIC SUBSTITUTIONS. 
33 
tating a hot solution of the sulphate of copper by caustic potash. The results agreed 
closely with one another, being 3° ’52 and 3 0, 53. Taking the mean of these numbers 
from 6°‘76, we have 3 0, 23 to express the heat due to the substitution of potash for 
oxide of copper. The result of the direct experiment was 3 o- 08. 
A similar comparison cannot be made with the salts of magnesia or lead, because 
an imperfect substitution takes place when their solutions are precipitated by potash. 
If we compare in like manner the other results contained in the paper before re- 
ferred to, it will be found that the differences between theory and experiment rarely 
exceed 0 o, 3, — a close approximation when the defective method of investigation 
formerly employed, and the great difficulty of obtaining accurate results with the 
insoluble bases are considered. 
It may be remarked that there is no notable difference in the heat developed during 
the solution of the oxides of zinc and copper in the hydrous and anhydrous states, 
which makes it probable that the heat due to the combination of those bases with 
water is not considerable. 
The preceding experiments appear to me to be sufficient to establish the accuracy 
of the general principle already stated, that when one base displaces another from 
any of its neutral combinations (all being taken in the state of dilute solution) the 
heat is always the same with the same bases, but in general different with different 
bases. The small deviations from this law in the case of the ordinary bases are not 
greater than we observe in other investigations connected with heat ; and I have be- 
fore pointed out many circumstances which tend to account for some of these devia- 
tions. The results obtained during the decomposition of the salts of water present 
more remarkable anomalies, as I have formerly shown. Of these, the greater deve- 
lopment of heat during the neutralization of the dilute sulphuric acid by alkaline so- 
lutions deserves particular notice, and still remains unexplained. The anomalies 
presented by the oxide of mercury and hydrocyanic acid, I have partly traced to their 
source. But the other results approximate too closely to one another to leave any 
doubt that the same principle applies to the decomposition of the salts of water as 
well as to that of the salts of other bases. 
I have not succeeded in connecting the thermal developments, as given by expe- 
riment, with any other property of the bases. In the following list I have arranged 
the bases hitherto examined in the order of the thermal results, attaching to each 
the number expressing the change of temperature produced when its, salts are de- 
composed by potash. 
CaO . . . . 
. . —0-36 
ZnO 
. . . +174 
BaO 
. . o-oo 
HgO. . . . 
. . . +T86 
8rO 
. . o-oo 
PbO 
. . . +2-82 + 
NaO 
. . -|-0-08 
CuO 
. . . +3-00 
AdH 2 0 . . 
• • +0-74 
AgO 
. . . +3-93 
MnO 
. . +1-07 
Fe^O. . . . 
. . . +4-09 
FeO 
. . +160 
MDCCCXLIV. 
F 
