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V. On the Heat disengaged during Metallic Substitutions. 
By Thomas Andrews, M.D., M.R.I.A., Vice-President of Queens College, Belfast, 8fc. 
Communicated by Michael Faraday, Esq., F.R.S., Sfc. ^c. 
Received December 16, 1847. — Read January 20, 1848. 
In the present communication 1 propose to give an account of some new investiga- 
tions on the heat disengaged in chemical actions, which may be considered a 
continuation of my former inquiries on the same subject*. The greater number of 
the experiments to be detailed in this paper were made some years ago, and the con- 
clusion at which I arrived was briefly announced in the Philosophical Magazine for 
August 1844. More recently, I have taken an opportunity to repeat many of my 
former experiments and to add new ones on the same subject, all of which confirm 
the general results formerly obtained. 
Having originally observed that although a very limited number of bases (potash, 
soda, barytes and strontia) develope nearly the same quantity of heat, when a 
chemical equivalent of each enters into combination with an acid, yet that the 
greater number of bases differ most widely from one another, when so treated, while 
on the other hand, that different acids (taken in the state of dilute solution) produce 
with the same base nearly the same amount of heat, I ventured to draw the general 
inference that the thermal effects produced are more intimately connected with the 
basic, or electro-positive, than with the acid, or electro-negative element. In con- 
formity with this view, it appeared probable that in the decomposition of solutions 
of neutral salts by the addition of bases or metallic bodies, the nature of the acid or 
electro-negative element of the compound would exercise no special influence on the 
result. I have already endeavoured to establish by experiment the truth of this 
principle in the case of basic substitutions, and, in the present memoir, 1 propose to 
extend the same general law to the other case, in which one metallic element re- 
places, or is substituted for another. 
Few chemical actions are more simple in their final results, or admit more easily 
of being varied without changing the general type of the reaction, than those which 
form the subject of the present inquiry. When a neutral solution of any salt of the 
black oxide of copper, as, for example, the sulphate, the chloride, or the acetate, is 
precipitated by metallic zinc, the final result is the substitution of an atom of zinc 
for an atom of copper in the solution, and the precipitation of an atom of copper. If 
* Transactions of the Royal Irish Academy, vol. xix. pp. 228, 293. Also Philosophical Transactions for 
1844, p. 21. 
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