434 Mr. Lubbock on the Heat of Vapours 



This difference between the original weight of the remainder 

 = 0*7500, which amounts to 0*2705, we may consider as 

 carbon. 



Now we calculated the amount of carbon to be 0*71188, 

 but as we find only 0*2705 grains of carbon, the difference 

 = 0*7118 — 0*2705 = 0*44138 carbon, must have been coun- 

 terbalanced by an equal quantity of oxygen to product; oxidum 

 ferroso-ferricum in the following way : — 



Oxygen 0*44138 



Iron 1*12268 



Oxidum ferroso-ferricum . . 1*26406 



Remaining iron 1*040728. 



The 2-604788 



will be therefore the calculated loss ; the actual loss on the 

 contrary was found as before mentioned = 2*64; the difference 

 between experiment and calculation amounts only to 0*035212. 



[To be continued.] 



LXIV. — On the Heat of Vapours and on Astronomical Re- 

 fractions. By John William Lubbock, Esq.^ Treas. U.S. 

 F.R.A.S. a?id F.L.S.i Vice- Chancellor of the University of 

 London J Sj-c.^ 



PREFACE. 



THE connexion between the temperature and the pressure 

 (or elasticity) of elastic vapours is a desideratum in Phy- 

 sics. A knowledge of it is indispensable to an exact theory of 

 the Steam Engine, to an exact theory of Astronomical Refrac- 

 tions, and to an accurate solution of other important pro- 

 blems. The want of it has hitherto been supplied by un- 

 satisfactory approximations; but these questions cannot be 

 completely investigated without a more careful attention to 

 the premises than has hitherto been possible, owing to a want 

 of the proper key to these researches, which consists in a know- 

 ledge of the mathematical law which connects the tempera-^ 

 ture and the pressure in elastic fluids, and which is required 

 in addition to the law of Mariotte and Gay Lussac to com- 

 plete their theory. 



If V represent the absolute heat or caloric, i the latent 

 heal, c the sensible heat or that which affects the thermometer, 



V= i -h c. 



* Reprinted, by the obliging permission of the author, from the original me- 

 moir lately published. London, 1840. 8vo, 



