1300 RESKARCHES ON EVArORATION AND DISSOCTATTON. 



liquids, chosen on account of their stability, and the oaHO 

 with which they can be obtained in a state of purity : chlo- 

 robenzene, bromobenzeno, aniline, methyl-salicylate, and 

 bromonaphthalene. The vapour-pressuros of mercury, as 

 determined by Regnault, were at first taken to be correct ; 

 but it was found subsequently that they required redeter- 

 mination. 



(6) Comparison of the vapour-pressures of the liquids 

 employed for maintaining constant temperatures led to 

 the discovery of four approximate relations connecting the 

 vapour-pressures of different substances; of these, two 

 apply also to the ratio between the heat of vaporization and 

 the increase of volume during the process of vaporization. 



By means of these relations, the correctness of our 

 measurements of the vapour-pressures of acetic acid was 

 confirmed; and while these relations were proved to be 

 applicable to all the substances investigated by Regnault 

 in his classical researches, with the exception of mercury, 

 and to the 28 ethers investigated by Schumann, as well as 

 to oxygen and ethylene, for which data are furnished by 

 Olzewski, the vapour-pressures of mercury and of the fatty 

 acids (the latter determined by Landolt), proved the solo 

 exceptions. 



(7) An investigation of the vapour-pressuros of mercury 

 at high temperatures by ourselves, and of the fatty acids 

 by Dr. Arthur Richardson, in this laboratory, proved that 

 they also formed no exception to the general rule. These 

 determinations also negative Kalilbaum's contention that 

 the vapour-pressures of stable substances measured by the 

 statical and the dynamical methods, are different. 



(8) It was found that these relations hold with the vapour- 

 pressures of solids, as well ;is of liquids ; and in a separate 

 paper, the data for solid and for liquid broniiiio and iodine 



