Laws of Molecular Force, 



21 



which thus becomes the fundamental equation for the elements 

 and the above types of compounds. For these types k there- 

 fore varies inversely as Mc, but Mc is m^ + m 2 c 2 + . . ., that 

 is the sum of the atomic specific heats, which for most atoms 

 are each nearly equal to 6*4, so that for these types Mc/6'4 is 

 equal to the number of atoms in the molecule, and accordingly k 

 is inversely proportional to the number of atoms in the mole- 

 cule. When we come to types such as RN0 3 , involving a 

 compound radical N0 3 , some of whose component atoms have 

 an atomic specific heat less than 6'4, k is inversely as the 

 number of radicals in the molecule, so that for RN0 8 it 

 remains 1/2 as for RC1, but Mc is no longer 2 x 6*4. The 

 case of R(N0 3 ) 2 is not so simple, but these matters will be 

 gone into later on ; at present we proceed with the application 

 of (0) to the types ROJ s , RC1 3 , and RC1 4 . 



The data and results for a number of haloid compounds of 

 these types are given in the next table, the melting-points 

 being as before taken from Carnelley's table and diagram, 

 and the densities used in calculating the molecular domains 

 being derived from various sources (chiefly F. W. Clarke's 

 collection of data in Smithsonian Miscellaneous Collections, 

 xii. and xiv.) ; the bracketed values of the molecular 

 domains are the approximate results of interpolation. 



Table XIV (Type RC1 2 ). 



Mg. 



T 



M/ p.. 



F 



L 2 . 



1180 



251 



5-8 



CL. B) 



i 2 . 

 981 

 43 6 

 7'3 



s 



T 



M/> . 

 (M 2 2)* 



T 



M/p 



F 



1170 



(31) 



6-9 



01 2 . 

 535 



494 



59 



r. 

 Cl 2 .* 



1098 



51-9 

 87 



2* 



971 



(56) 



8-6 



Er 2 . 



903 



62 4 



90 



Zn. 



Br 2 . 



667 

 61-8 



7-7 



I 2 . 



889 



(71) 

 9-7 



780 



77-4 



9-6 



I 3 . 

 719 

 679 



8-6 



F 



X 2- 



1170 



248 



59 



F 2 . 

 1180 

 36-2 



7-7 



Cl 2 . 



814 



50-5 



7-5 



Ca. 



Cl 2 * 

 992 



50 



7'9 



Ba. 



Br 2 



949 



603 

 8-9 



1181 



Br 2 . 

 1085 

 541 703 

 95 107 



Cd. 

 Br 2 . 

 844 

 579 

 85 



904 



(75) 

 100 



929 



(85) 



111 



J, 

 677 

 79-4 

 91 



* Compare with these the values in Table IX. from surface- tensions, 

 namely, 9'8 for CaCl 2 , 10"6 for SrCl 2 , 12'4 for BaCl 2 , 6;3 for AgCl, and 

 6*7 for AgBr, which are all about 1*2 times the values in this table, but 

 the values of the surface-tensions are uncertain. 



