﻿38 On the Heat Developed in the Combination of Acids and Bases, 



Appendix. 

 In the following Tables I have given the results described in 

 this communication and those of 1841 in a form which admits 

 of comparison with one another, and with those of MM. Favre 

 and Silbermann. I have also added a few determinations re- 

 cently made by M. Thomsen of Copenhagen*. It will be seen 

 that the original experiments of 1841 exhibit, on the whole, a 

 fair agreement with those now communicated to the Society. 

 Prom the small scale on which they were performed (the whole 

 weight of the solutions after mixture being less than 30 grms.), 

 the imperfect form of the apparatus, and the uncertainty of the 

 thermometric indications, I have indeed been surprised to find 

 them so near the truth. The results of MM. Favre and Silber- 

 mann do not exhibit the precision which might have been ex- 

 pected from the high character of those experimentalists, and 

 from the accuracy of other parts of their great work. The mer- 

 curial calorimeter employed by them appears to have been little 

 adapted to its purpose ; but after making due allowance for its 

 imperfections, I am at a loss to account for the serious errors 

 into which they have fallen. M. Thomsen's experiments have 

 evidently been made with care, and his results agree compara- 

 tively with my own ; but the absolute amount of heat obtained 

 by him falls far short of what I have found. It is indeed much 

 easier to obtain results relatively than absolutely correct. The 

 numbers given in this paper will, I believe, be found rarely to 

 differ relatively more than g\> o from the truth ; but they may 

 hereafter require a small correction in respect to their absolute 

 value. That correction, however, can scarcely be more than 

 -£$ of the whole amount; and I have little doubt that the 

 number, for example, given by Thomsen to express the heat dis- 

 engaged in the combination of soda with nitric acid will prove to 

 be as far below the true number as that given by MM. Favre 

 and Silbermann is above it. 



Table I. — Potash. 



Acid. 



Andrews, 

 1841. 



Favre and 

 Silbermann. 



Andrews, 

 1870. 





16330 

 15076 

 14634 

 14771 

 14257 

 13612 



16083 

 15510 

 15656 

 14156 

 13973 

 13425 



16701 

 14800 

 14940 

 15124 

 13805 

 13508 



Nitric 



Hydrochloric 



Oxalic 



Acetic 



Tartaric 





observations of Graham confirm the statement that no heat is evolved in 

 the formation of any double salt. Memoirs of the Chemical Societv, vol. i. 

 p. 83. 



* PoggendorfFs Annalen, vol. cxxxviii. p. 78. 



