686 



SCIENCE PROGRESS 



In the first case Hg seems to impose its value on Na, and in the 

 second there seems to be association of NaHg in the former 

 with three atoms of mercury. 



The M.P.'s show that NaHg 2 is quite different from all the 

 others, because its M.P. is considerably higher than those of 

 NaHg and NaHg 4 , whereas it should be intermediate. 



It is evident from this that considerable modifications of the 

 free atomic volumes can occur, even in such loose combinations 

 as alloys, and that in spite of such changes the Additive 

 Principle holds. 



(ii) The Chlor-Brom-Iodides of Silver, which have been studied 

 by Rodwell {Phil. Trans. 1882, 1140), present some remarkable 

 examples of the modification of volumes in conformity with a 

 simple numerical relationship. 



We give first of all the following, which illustrate the prin- 

 ciple of addivity without great modification of the free values 

 (Rodwell, Phil. Trans. 1882, 1160). 



The combined volumes of Cul and Agl are respectively 32-9 

 and 41-3. 



Free Volumes: 



Cul 33-3 Agl 415 

 The volumes of both are diminished slightly in the above com- 

 binations, but the volumes are perfectly additive. 



As before stated, great modifications can occur, either so as 

 to conform with some simple spatial relation, or even, as in the 

 case of the amalgams previously studied, in what seems an 

 arbitrary manner. 



They may be studied at o° and at their respective M.P.'s. 



The data for the free simple salts are : 



