﻿36 Dr. T, Andrews on the Heat Developed in 



remarked that the oxalic acid disengages from o, 022 to o, 058 

 more heat in combining with these bases than the hydrochloric 

 acid, and from o, 065 to O 0, lll more than the nitric acid. The 

 conclusion of MM. Favre and Silbermann, that the organic acids 

 (oxalic, formic, acetic, &c.) disengage sensibly less heat than 

 the mineral acids, is thus entirely disproved, and the original 

 results recorded in my work of 1841, according to which the 

 oxalic acid disengages at least as much heat as the nitric, phos- 

 phoric, arsenic, hydrochloric, hydriodic, boracic, and other mi- 

 neral acids (with the exception of the sulphuric acid), are fully 

 confirmed. The tartaric, citric, and succinic acids, it is true (as 

 was also shown in the same work), give out about ^ less 

 heat than the average of the other acids ; but the acetic and 

 formic acids fall scarcely -^ below the mean, and the oxalic 

 acid is always above it. These results, in all their main features, 

 are fully corroborated by the experiments recorded in this paper, 

 which were performed with a more perfect apparatus and a more 

 exact thermometer than I had at my command in my earlier in- 

 vestigations. A reference to the same paper will show that 

 while acids differing so widely from one another as the oxalic, 

 phosphoric, arsenic, nitric, hydrochloric, and boracic acids 

 scarcely present any sensible difference in the quantities of heat 

 which they disengage in combining with the bases, and while, 

 of the other acids examined, the sulphuric acid (and probably 

 also the sulphurous acid) presents an extreme deviation of 

 about one-eighth above the mean, and the tartaric- acid group 

 a deviation of about ^ below it, the bases, on the contrary 

 (and the subsequent researches of Favre and Silbermann have 

 confirmed this result), differ altogether in thermal power from 

 one another. Thus equivalents of the oxides of magnesium and 

 of silver give out 4°*1 and 1°'8 of heat respectively in combi- 

 ning with nitric acid, the former oxide having therefore 2*3 times 

 the thermal power of the latter. Yet, as is well known, both 

 these bases fully saturate the acid, and the resulting solutions 

 are even neutral to test-paper. For these reasons I have no 

 doubt whatever that the first law, as enunciated in 1841, is the 

 expression of a true physical law, and that in the combination 

 of acids and bases in presence of water the heat disengaged is 

 determined by the base and not by the acid. It is true that, in 

 this as in similar physical inquiries, experimental results cannot 

 immediately be obtained free from complication or disturbing in- 

 fluences. The same remark applies to the experimental proof 

 of the great law discovered by Dulongand Petit, w T hich connects 

 the specific heats and atomic weights of the elementary bodies, 

 and also to that of the remarkable relations discovered by Kopp 

 between the composition and boiling-points of many organic 



