684 



SCIENCE PROGRESS 



In Combination : 



The Table shows conclusively that the augmentations in volume 

 on liquefaction depend on the number of atoms. The expan- 

 sion is the same for a Pb as for a Sn atom, for Sn = Pb = + 0*44 ; 

 but in the free state they are different, for Sn = + 0*49 and 

 Pb = + 0*62. A modification of this space augmentation per 

 atom has occurred, in a similar manner to the variation or 

 modification of the M.P. on combination. That there has been 

 an alteration in the volume of each atom individually, and not 

 an indirect variation due to the change in the amount of play 

 space of the whole molecule, seems very probable. 



A study of the amounts of heat absorbed by 100 grammes of 

 the substance as the temperature has been raised from ioo° to 

 360 has been shown by Spring {Bull. Acad. Belg. [3], 11, 355, 

 1886) to be greater than that absorbed by an amount of matter 

 in the free state equivalent to the sum of the constituents. The 

 excess varies with the composition. The results may be ex- 

 plained by assuming that the metals form unstable compounds, 

 which, on being heated, break down into their constituents. 

 The result of Magies' work on " Specific Heats " {Bull, of Amer. 

 Phys. Soc, April 27, 1 901) greatly favours our view of the question, 

 for even in solution salt molecules and ions are able to exert an 

 attracting influence on molecules of the solvent for some con- 

 siderable distance, so that possibly complex aggregations of 

 molecules about the ions result. 



If this be so, the Additive rule already noticed is independent 

 of whether the substance is solid or liquid, or whether the atoms 

 are associated or dissociated. 



Modifications in Volume associated with Physical Changes in 



Compounds 



It is extremely probable that ma^r differences occur in the 

 nature of alloys which are indicated by their thermal and 



