322 HISTORY OF CHEMISTRY. [LECTURE XV. 



any considerable result; and quite a number of gases were 

 liquefied by him in an extremely simple and ingenious 

 manner. 145 He operated upon the small scale only, whilst 

 carbonic anhydride was first liquefied in considerable quantities 

 by Thilorier. 140 Faraday then continued his investigations, 147 

 making use of the knowledge already gained by Thilorier, but 

 without obtaining any result in the cases of hydrogen, oxygen, 

 nitrogen, carbonic oxide, nitric oxide, etc. Natterer was like- 

 wise unable to liquefy hydrogen although he exposed it to a 

 pressure of 2790 atmospheres. 148 



It was only in 1877 that Pictet 149 and Cailletet 15 succeeded, 

 nearly simultaneously, in liquefying the majority of the so-called 

 permanent gases ; but it was not possible at that time, by the 

 aid of the methods and appliances employed by these investi- 

 gators, to obtain the liquids in quantity and to determine their 

 physical constants (boiling-point, critical temperature, density, 

 etc.). This was first accomplished by Wroblewsky, m whose 

 research may be regarded as an example of finished skill. 



The intimate connection between physics and chemistry, 

 which is apparent in the matter just dealt .with, makes itself 

 still more clearly manifest when we pass on to thermo-chemistry. 

 This is a subject which is of equal importance to both branches, 

 and, moreover, it has been almost entirely elaborated by men 

 belonging to the two sciences. Lavoisier and Laplace may be 

 looked upon as the founders of thermo-chemistry, not only on 

 account of their experimental researches on specific and latent 

 heats and on heats of combustion, but also on account of their 

 masterly definitions, 152 and, especially, of the fundamental (if 

 not quite precisely formulated) principle which they deduce 

 from the mechanical law of the conservation of energy : 



The heat liberated during combination or change of state 



145 Phil. Trans. 1823, 160, 189 ; Alembic Club Reprints, 12, 5, 10. 

 146 Ann. Chim. [2] 60, 427. 147 Phil. Trans. 1845, 155 ; A.C.R. 12, 33. 

 148 Pogg. Ann. 94, 436. 149 Comptes Rendus. 85, 1214, 1220; Ann. 

 Chim. [5] 13, 145. 15 Comptes Rendus. 8$, 851, 1016, 1213 ; Ann. 

 Chim. [5] 15, 132. 151 Monatshefte. 6, 204. 1S2 Compare p. 26, 



