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V. — On the Heat Developed in the Combination of Acids and Bases. Second 

 Memoir. By Thomas Andrews, M.D., F.R.S., Hon. F.RS.E., Vice- 

 President of Queen's College, Belfast. 



(Read 6th June 1870.) 



In a paper communicated to the Eoyal Irish Academy in 1841, I gave an 

 account of a large number of experiments on the heat disengaged when acids and 

 bases, taken in the state of dilute solution, enter into combination, and when 

 bases, insoluble in water, are dissolved in dilute acids. The following general 

 conclusions or laws were deduced from those experiments : — 



Law 1. — The heat developed in the union of acids and bases is determined 

 by the base and not by the acid, the same base producing, when combined with 

 an equivalent of different acids, nearly the same quantity of heat ; but different 

 bases, different quantities. 



Laiv 2.- — When a neutral is converted into an acid salt, by combining with 

 one or more atoms of acid, no change of temperature occurs. 



Law 3. — When a neutral is converted into a basic salt, by combining with 

 an additional proportion of base, the combination is accompanied with the 

 evolution of heat. * 



Three years later I laid before the Royal Society of London the results of 

 an experimental investigation of the heat developed when one base is substi- 

 tuted for another in chemical compounds. The law deduced from this inquiry 

 is implicitly involved in the foregoing, of which it may indeed be regarded as a 

 necessary consequence. It was enunciated in the following terms : — 



Laiv 4. — When one base displaces another from any of its neutral combina- 

 tions, the heat evolved or abstracted is always the same, whatever the acid 

 element may be, provided the bases are the same.t 



Finally, the law of metallic substitutions, first announced in the " Philo- 

 sophical Magazine" for August 1844, was thus stated in a paper published in 

 the "Philosophical Transactions" for 1848. 



Law 5. — When an equivalent of one and the same metal replaces another 

 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. 



In 1845 a paper appeared by Graham on the heat disengaged in combina- 

 tions, the second part of which refers to the heat produced when hydrate of 



* Transactions of the Eoyal Irish Academy, vol. xix. p. 228. 

 f Philosophical Transactions for 1844, p. 21. 



VOL. XXVI. PART I. Z 



