266 Mr. Herapath on True Temperature, and the [Oct. 



vious and subsequent temperatures, that it is not surprising an 

 instance of perfect equality has, perhaps, not been discovered. 

 By our theory, a difference of one particle in a thousand at the 

 temperature of ice melting, would be enough to change the tem- 

 perature of the result a degree of Fahrenheit; and one in a 

 hundred would make near 10°. At the higher temperatures the 

 same difference in the numbers of the particles would occasion 

 a still greater difference between the temperatures. 



Notwithstanding we can hardly, under such circumstances, 

 expect to, and cannot, that 1 know of, instance a case of perfect 

 equality in the previous and subsequent temperatures, where a 

 chemical change has been effected, yet there are many pheno- 

 mena which prove its possibility. Thus, to go no further than 

 the cases 1 have cited, in gun and fulminating powders, there is 

 a conversion of solids into airs accompanied with a very consi- 

 derable increase of temperature ; while, in general, such conver- 

 sions are productive of very considerable diminutions of tem- 

 perature. Now if the conversions of water, vinegar, alcohol, &c. 

 into airs are attended with diminutions of temperature, amount- 

 ing to between 800° and 1000° of Fahrenheit, as philosophers 

 tell us, what reason can be assigned why the gasefyings of those 

 powders, which, in the general view of things, appear to be 

 parallel cases, should be attended with so great augmentations 

 of temperature ? Do not such phenomena prove that they are 

 the demonstrated extremes of an equally possible mean? Besides 

 in some of the other cases that I have mentioned, for instance 

 the condensation of sulphuretted hydrogen gas and ammonia 

 into a solid, the rise of temperature is so small compared to that 

 which results from the condensation of aqueous vapour into a 

 fluid only, that it might almost be neglected. Here then are 

 examples of gases being converted into solids with scarcely any 

 elevation of temperature ; while, by the ordinary examples of the 

 generality of other similar phenomena, the elevation ought to 

 have been upwards of a thousand degrees. In the absence of a 

 direct particular case, such facts are surely as decided a proof 

 as can be expected of the accuracy of our general conclusion ; 

 namely, that it is possible for a chemical change to take place 

 without any alteration of temperature. 



Many other examples might easily be advanced of the facility 

 with which the various phenomena connected with a change of 

 state flow from our principles. We might also extend the same 

 views to the phenomena of combustion, and might show that 

 they all flow from the same simple principle ; — adaptation of figure 

 in the particles of the supporters and combustibles, and inadap* 

 tation in the supporters and incombustibles ; but as I have 

 already said much more of my general views of the phenomena 

 of the change of state than is suited to a paper of this kind, I 

 shall reserve a further detail of my inquiries into this part of the 

 subject to another opportunity. 



