76 Mr Potter mi the Specifc Heats nf Metals, $<: 



ric. The results of my experiments gave me numbers so much 

 smaller than I had expected from a review of Mr Dalton's de- 

 terminations for iron, copper, and tin, that I resolved to seize 

 the opportunity of my first leisure time to enter into further 

 investigations of the specific heats of the metals generally. 



Mr Dalton has given a very extensive table of the specific 

 heats of different substances, which in the metals are little dif- 

 ferent from the older determinations of Irvine, Wilcke, and 

 Crawford ; but these numbers are, I think, frequently too 

 oreat bv ^ to A P art > f° r which allowance should be made 

 when these tables are used. 



MM. Dulong and Petit, who have so ably examined the 

 phenomena of cooling bodies, presented also to the Academy 

 of Sciences in 1819* an essay, of which the principal purport 

 is the specific heats of certain of the metals determined by them, 

 coupled with important theoretical considerations. In the 

 course of their essay they take the opportunity to stigmatize 

 as exceedino-lv erroneous, all the results of former chemists ex- 

 cept those of their own countrymen. But before passing so 

 sweeping a censure, it would have been as well if they had 

 been sufficiently circumspect in their own experiments, to pre- 

 vent a recoil of it with double force on their own labours. The 

 method they made use of in this instance to find the capacities 

 of the metals for caloric is the following : — The metal to be 

 examined was reduced to a very fine powder, and pressed 

 closely into a small and very thin cylinder of silver, having a 

 thermometer placed in its axis. When the whole was adapted 

 to a suitable apparatus, the capacity was deduced from the 

 rate of cooling indicated by the thermometer ; the quantity of 

 even the heaviest metals required for the experiment being- 

 something less than an ounce English. It must be clear to 

 every one, that, when we resort to intricate or elegant methods 

 of experimenting, our vigilance and suspicion ought to be awak- 

 ened, particularly when our results differ suddenly from the 

 determinations of those who have used simpler apparatus ; and 

 it appears unaccountable, that, when MM. Dulong and Petit 

 found their results for most of the metals of less capacity than 

 silver differ so greatly from the determinations of Mr Dalton, 

 of Wilcke, and of Crawford, they did not seek to prove them 



* See Annates de Chimie et de Physique for 1319. 



