﻿32 Dr. T. Andrews on the Heat Developed in 



least as much heat in combining with the bases as the hydro- 

 chloric, nitric, and several other strong mineral acids. 



The experiments to be described in this paper were made some 

 years ago ; but their publication has been deferred from acci- 

 dental circumstances. I have, however, recently repeated a few 

 of the more important of them with a slightly modified form of 

 apparatus. The solutions were taken in so dilute a state that 

 the heat disengaged never exceeded 3° # 5 C. A standard solu- 

 tion of sulphuric acid was prepared and carefully analyzed, by 

 precipitating a given weight with a soluble salt of barium, and 

 weighing the sulphate of barium. The strength of the alkaline 

 solutions was adjusted with great care by means of this standard 

 acid. The same solution of each alkali was employed in all the 

 experiments, and the quantity used in each experiment was de- 

 termined by careful weighing. The acid solution was of such a 

 strength that, after being mixed with the alkali, an excess of two 

 or three per cent, of acid was present. The alkaline solution 

 was contained in a light glass vessel, in which a large platinum 

 crucible holding the acid was carefully floated. By giving a 

 rapid rotation, by means of a light stirrer, to the acid solution 

 in the platinum crucible, a perfect equilibrium of temperature 

 was soon established between the two liquids. The initial tem- 

 perature of the solutions was usually about 1°'5 below that of 

 the air, and the final temperature of the mixture about 1° # 5 

 above it. The corrections for the heating and cooling action of 

 the surrounding medium were determined with great care. The 

 mechanical process of adding the acid to the alkaline solution pro- 

 duced no change of temperature ; and as the heat disengaged in 

 the combination raised the liquid almost instantly to the maxi- 

 mum temperature, the whole correction required was for cooling. 

 The first temperature was read one minute after the addition of 

 the acid to the alkaline solution, the mixture being stirred du- 

 ring the whole of that time. If 8 represents the correction, and 

 e the excess of temperature above the air in Centigrade degrees, 

 the value of 8 will be given by the following expression : — 



S=ex0°-012. 



As a proof of the accuracy of the method of mixture adopted 

 in this inquiry, I may mention that, being desirous to know 

 whether the dilute acids employed in these experiments produced 

 any change of temperature when mixed with water, I made the 

 experiment with nitric acid by the method just described, sub- 

 stituting water for the alkaline solution, with the unexpected 

 result of a fall of 0°*01. On varying the conditions of the ob- 

 servation, so as to obtain a larger effect, it was ascertained not 

 only that a diminution of temperature had actually occurred, but 



