Atomic Laws of Thermochemistry . 13 



above assumption. From what is known of the saturation 

 densities of ordinary vapours, it is likely that with the true 

 volume of mercury vapour the value 14 for the latent heat 

 would be reduced to at least 13, of which about one eleventh 

 part is due to doing external work ; so that the pure latent 

 heat of liquid mercury is about 12 kilocalories for the 

 gramme-atom. The latent heat of fusion of 200 grammes of 

 solid Hg is *6 kilocalories ; so that the latent heat of vaporiza- 

 tion of solid mercury is about 13 kilocalories per gramme- 

 atom. The value calculated in Table I. for the latent heat 

 due to molecular force is 7*8, and therefore the total latent 

 heats would appear to be 1*6 times the tabulated values. 



When the values of I are calculated for the metals by equa- 

 tion (7) with Quincke's values for the surface-tension, certain 

 discrepancies with the values in Table I. appear, which were 

 remarked on in " A Kinetic Theory of Solids " in an indirect 

 manner. These discrepancies now appear to be due to varying 

 molecular complexity in a few of the metals, and it would lead 

 us too far to discuss them at present. In the case of com- 

 pounds the two equations (7) and (13) give accordant results, 

 to which we will proceed. We will first give a table for 

 those binary compounds for which the data for both methods 

 are available, so that the two sets of values for M 2 / may be 

 compared. In the following table the values of the suriace- 

 tension a m are given in gTammes weight per metre, and when 

 taken from Quincke are denoted by Q and from Traube by T. 

 The melting-points here and in the following table are taken 

 chiefly from Carnelley (Journ. Chem Soc. xxix., xxxiii., 

 xxxv., and xxxvii. ; Phil. Mag. 5th ser. vol. xviii.), and the 

 densities from Clarke's ' Constants of Nature ' and Landolt 

 and Bornstein's Tabellen. 



Table II. 



LiOl. NaCl. NaBr. KF. KOI. 



* IU 121 Q. 11-6 T. 10-5T. 14-2T. 100T. 



p 2-00 215 3-00 2-45 1-98 



M/p 21-2 27-2 34-4 237 376 



T 870 1045 981 1060 1007 



UH(J) 18-4 27-0 33-6 261 -39 6 



M 2 £(13) 20/2 32-5 40-9 32-5 46'1 



KBr. KI. AgCl. AgBr. CaCl 2 . 



« m ..< 93T. 8-5T. 19-0Q. 173Q. 153 Q. 



p .... 2-69 308 5-55 6-42 2'22 



M/p 44-2 53-8 258 29-3 50-5 



T 972 907 724 700 992 



•M'^(7) 47-6 60-8 39'6 44-9 95-9 



M 2 ^(13) 56-2 67-3 25'0 29-1 62-5 





