Mr. H. J. Brooke on the Beudantite of Levy. 21 



From this, in the first place, we derive the proposition deve- 

 loped also by Carnot ; whe7i a gas, without alteration of tempera- 

 ture, changes its volume, the quantities of heat developed or absorbed 

 are in arithmetical progression, while the volumes are in geometrical 

 progression. ^^. 



Further, let the complete expression for R= ^-^-^ be set in 



equation (18.), and we obtain , . 



Q-Qo=Ai,o''olog-. . . .' .' (19.) 



If we apply this equation to diiferent gases, not directing our 

 attention to equal weights of the same, but to such quantities as 

 at the beginning embrace a common volume Vq, the equation 

 will in all its parts be independent of the peculiar nature of the 

 gas, and agrees with the known proposition to which Dulong, 

 led by the above simple relation of the quantity ^ — 1, has given 

 expression : that when equal volumes of different gases at the same 

 pressure and temperature are compressed or expanded an equal 

 fractional part of the volume, the same absolute amount of heat is 

 in all cases developed or absorbed. The equation (19.) is however 

 much more general. It says besides this, that the quantity of 

 heat is independent of the temperature at which the alteration of 

 volume takes place, if only the quantity of gas applied be always 

 so determined that the original volumes Vq at the diiferent tem- 

 peratures shall be equal; further, that when the original pressure 

 is in the different cases different, the quantities of heat are thereto 

 proportional. 



[To be continued.] 



II. On the Beudantite of Levy. By H. J. Brooke, F.R.S."^ 



HAVING had the pleasure last week of a personal commu- 

 nication with M. Des Cloizeaux, and having shown him 

 Levy's specimen of this mineral, he at once stated that it differed 

 entirely from that examined by himself and M. Damouras Beu- 

 dantite, as well as from every other specimen under the same 

 name which he had seen. He said that he was not aware of the 

 existence of any mineral resembling Levy's in any collection on 

 the Continent, and that he was inclined with Levy to regard his 

 specimen as belonging to a separate species. The mineral known 

 as Beudantite on the continent appears to be only an impure 

 variety of cube ore of the usual form. 



June 9, 1851. 



* Communicated by the Author. 



