Dr. Andrews on the Heat developed, Sfc. 229 



acid required to neutralize the alcali. After the liquids had acquired the same 

 temperature, they were mixed together in the jar containing the alcali, and the 

 increase of heat carefully observed by a delicate thermometer. This process 

 was adopted from the facility of its execution and the uniformity of its results. 

 It is, however, obvious, that a large portion of heat would be absorbed by the 

 glass vessel ; and it was, therefore, necessary to establish, by a series of inde- 

 pendent experiments, the corrections to be applied to the temperatures thus 

 obtained. 



3. As a basis to this whole investigation, the heat developed in the combina- 

 tion of nitric acid and potash was carefully determined. But before describing 

 the method employed, I must anticipate an observation which will be afterwards 

 proved, viz., that the same amount of heat is developed when a given quantity 

 of an alcali is united to an acid, whether the acid added be just sufficient to 

 neutralize the alcali, or be considerably in excess.* The addition of a slight 

 excess of acid does not, therefore, in any way interfere with the results, except 

 in so far as it renders them more uniform and certain, by producing a rapid and 

 complete neutralization of the alcali. 



4. A cylindrical vessel of very thin brass was procured, capable of containing 

 rather more than the quantity of liquid employed. Into this vessel was introduced 

 the solution of caustic potash, the weight of which solution was about nine times 

 greater than that of the dilute nitric acid destined to neutralize it. This vessel 

 was so thin that we may assume, without any sensible error, its temperature to 

 have been identical with that of its liquid contents. It weighed 6.63 grammes, 

 which, assuming the specific heat of brass to be .094, is equivalent to 0.623 gr. 

 water. 



5. As the weights of the glass and mercury in the bulb and immersed 

 portion of the tube of the thermometer were both unknown, I was obliged to 

 have recourse to a direct experiment, in order to ascertain their equivalent of 

 water. For this purpose, 30 grammes of water (the quantity of liquid usually 

 employed) were introduced into the brass vessel, and the increase of its tempera- 

 ture carefully observed, when the thermometer, previously heated through a 



• These observations, as well as others of a similar kind in subsequent parts of this paper, refer 

 always to dilute solutions, such as are employed in these experiments. 



