76 REPORT—1849. 
and other metals were also tried, but the solution did not proceed with suffi- 
cient energy. 
The numbers 5857 and 2578 obtained above, are very nearly in the same 
ratio as 5366 and 2394, which, according to my experiments (and their results 
differ little from those of Dulong), express the quantities of heat set free by 
the combustion of zinc and copper in oxygen gas. This shows clearly that 
the oxidation of the metals is the principal cause of the heat produced during 
their solution in nitric acid. Other causes of thermal change however exist, 
which must exercise a considerable influence. Such are the combinations 
of the oxide with the nitric acid, the separation of the elements of a portion 
of the nitric acid during the solution, and the condensation of the oxygen gas 
during the combustion. From these and other circumstances, it is not un- 
likely that the numbers expressing the quantities of heat disengaged in these 
reactions will not be found in all other cases to be so nearly in the same 
ratio as in the foregoing examples; but it may be presumed that the general 
results will be the same, and that those metals which produce a greater 
amount of heat by their combustion in oxygen will also produce a greater 
amount of heat when dissolving in nitric acid. 
The heat produced by the solution of copper in nitromuriatie acid is, 
according to the result of a single trial, about +th less than that produced by 
its solution in nitric acid. 
Metallic substitutions.—I have lately treated this part of the subject at so 
great length in a paper published in the Philosophical Transactions, that I 
shall here only transcribe the general result of the investigation. It is thus 
expressed :—‘ When an equivalent of one and the same metal replaces an- 
other in a solution of any of its salts of the same order, the heat developed 
is always the same; but a change in either of the metals produces a different 
development of heat.” This is evidently an analogous law to that already 
stated for the thermal changes which accompany basic substitutions. The 
numerical results are however entirely different in their details. 
Combustions in Oxygen Gas.—Since the time when Lavoisier published 
his celebrated experiments on the heat produced by combustion, the subject 
has frequently engaged the attention of chemists. But few results were ob- 
. tained of any scientific value, till the posthumous publication of Dulong’s 
valuable researches, which have formed the basis of all subsequent inquiries. 
More recently, Grassi and Fabre and Silbermann have examined thesame sub- | 
ject, and I have myself lately published a set of experiments upon it, which | 
were made some years ago. With the exception of some of Grassi’s results, 
the numbers obtained by the different experimenters agree very nearly with 
each other, and we may therefore consider the quantities of heat developed 
by the combination of oxygen with the more important simple bodies and 
with some of their compounds to be determined with considerable precision. 
Fabre and Silbermann have also examined the combustion of carbon in the 
protoxide of nitrogen. A tabular view of nearly all the numerical results 
hitherto obtained, will be found in the edition of Gmelin’s Hand-book of Che- 
mistry recently published by the Cavendish Society. I shall here therefore 
confine myself to a few general observations. “ 
The following bodies in their ordinary physical states, viz. hydrogen, car- 
bonic oxide, cyanogen, iron, tin and antimony, disengage nearly the same 
amount of heat in combining with an equal volume of oxygen. The num- 
bers which express the heat of combination in these cases do not in fact differ 
from one another more than j,th part of the whole quantity,—a difference 
which is nearly within the limit of the errors of experiment. This observa- 
tion applies only to the quantities of heat actually obtained by experiment. 

