ON THE HALOGEN HYDKIDES AS CONDUCTING SOLVENTS. 



Ill 



KOPP has shown that the molecular volume of a liquid at its boiling-point is an 

 additive property, being equal to the sum of the atomic volumes of the component 

 elements. Certain elements, however, such as oxygen, appear to possess two values 

 for the atomic volume, depending on the nature of the linking of the oxygen to the 

 other atoms in the molecule. 



It has also been shown that, in the case of the elements chlorine, bromine, and 

 sulphur, the atomic volumes calculated from the density of compounds containing 

 them are the same as those obtained from the densities of the pure elements. We 

 have calculated the atomic volumes of the elements chlorine, bromine, iodine, sulphur, 

 and phosphorus from the densities of their respective hydrides, in order to see how 

 the values so obtained agree with those given by KOPP and others. 



The results of these calculations are given in Table IV., which contains D, the 

 densities of the compounds at their respective boiling-points, the molecular volume 

 M/D, and the atomic volume A' of the halogen elements. 



The values of these are invariably higher than those of KOPP, which are given 

 under A, in the fifth column. It is possible that this discrepancy is due to a variation 

 in the atomic volume of hydrogen, which has accordingly been calculated from each 

 compound by subtracting the figures in the fifth column from those in the third. 



The values for A, so obtained, are given in the last column, and are uniformly 

 higher than 5 '5, which is the number found from the study of organic compounds. 



TABLE IV. Molecular Volumes at Boiling-point. 



* MASSON. t THORPE. 



The Molecular Surface Energies. 



The molecular surface energies were measured by RAMSAY and SHIELDS' method, 

 slightly modified in order that the measurements might -be made at low temperatures. 

 The apparatus (fig. 5) consisted of a tube b, 6 centims. long and 1'3 centims. in 

 diameter, which was provided with a small side tube d, and joined to a two-way 

 stop-cock by a long tube a. 



A small glass scale s, which had been very carefully calibrated, was securely fixed 

 inside b. The capillary c was sealed to a long tube g, in the manner described by 



