ACCOMPANYING BASIC SUBSTITUTIONS. 
31 
under consideration. We know that the substituting base existed in the state of a 
hydrate before mixture, and that after mixture the displaced base is also obtained in 
the same state. But we have no means of discovering with certainty in what state 
these bases exist in the solutions of their neutral combinations. If we assume that 
they exist in the state of hydrates, then the numbers given before will express exactly 
the heat arising from the chemical substitutions. But if we suppose that the potash 
separates from its combination with water, and the lime on the other hand unites 
with water during the course of the experiments, then these numbers will be the 
general result of a series of complicated changes. Other suppositions may be made, 
but we cannot prove the truth of any of them. One thing is certain, that whatever 
these unknown changes may be, they will be precisely similar when the bases em- 
ployed are the same. Hence the foregoing experiments are sufficient to prove that 
with the same bases, the heat arising from basic substitutions is always the same, 
although the numbers may not express the entire change of temperature due to that 
cause. 
Among the circumstances which may perhaps be supposed to influence these 
results, are the changes of temperature arising from the solution of the saline com- 
pounds in water, — a subject recently investigated by Mr. Graham. But although it 
is true that a different salt remains in solution after substitution from that which was 
present before, yet it must be observed, that neither salt during the process assumes 
the solid state, and the changes of temperature in question are essentially dependent 
on that condition. For this reason, it appears to me that the thermal effects arising 
from solution are not in any way brought into action in the course of these experi- 
ments. 
The same general principle will be found to include nearly all the thermal results 
I formerly described, as arising from the action of bases and dilute acids upon one 
another, and upon solutions of neutral salts. In cases where the same base (as before 
mentioned) displaced water from any of its combinations with the acids, the heat 
evolved was nearly (but not exactly) the same. On the contrary, where no basic 
substitution occurred, there was either none, or a very slight variation of temperature. 
As examples of the latter, I may refer to the absence of any variation of temperature 
when solutions of a neutral salt and hydrated acid, capable of combining to form an 
acid or double salt, are mixed. Mr. Graham has indeed lately made the observation, 
that the formation of certain acid sulphates is attended with a diminution of tempera- 
ture, but the change of temperature so produced is of small amount compared with 
that arising from basic substitutions. It is difficult to prove that combination actually 
takes place when solutions containing the proximate constituents of an acid or double 
salt are mixed. But, as far as I have investigated the subject, the thermal properties 
of the solutions thus formed are identical with those of solutions prepared by dis- 
solving the crystallized acid or double salt in water. Thus, if we prepare solutions 
of crystallized binoxalate and quadroxalate of potash, and add to them exactly the 
