362 Dr. A. Ransome on some of the 



differs from molecular attraction in the power of producing com- 

 bination. 



When molecular operations take place between the particles 

 of bodies of dissimilar chemical composition, the following con- 

 ditions are found to favour the production of molecular and che- 

 mical changes : — 



(1) That two or more of the substances submitted to mole- 

 cular influences have a more or less powerful attraction for one 

 another. 



(2) That their physical condition is favourable to molecular 

 action. 



(3) That the molecular agent Or catalyte has very low chemical 

 affinities for the substances acted upon. 



(4) That the molecules of the catalyte are free. 



Each of these conditions will be considered separately, and 

 their bearing upon different molecular actions will be noticed 

 somewhat in detail. 



1. Of Molecular Affinity, 



It is a question whether the real molecular force of all sub- 

 stances may not be the same in degree. All substances may 

 possess absolutely the same amount of molecular force ; but from 

 their varying chemical affinities, and from the various extent to 

 which they are subject to the different affections of matter, they 

 may not be able equally to exert their molecular power. 



The molecular force depends so greatly upon the degree of 

 approximation of the particles, and this must be so seriously 

 affected by variations in the above-mentioned conditions, that 

 we cannot affirm that different manifestations of the molecular 

 influence of different substances may not be governed by these 

 conditions, and that the molecular force is not the same in all 

 substances. Until we can appreciate the minute differences in the 

 degrees of approximation of substances to one another during 

 any molecular action, no absolute measure of molecular force can 

 be applied. Professor Tyndalland M. H. Ste.-Claire Deville, in 

 some of their recent researches, seem to have approached, 

 although they have not as yet effected, the solution of this pro- 

 blem, and no certain means are yet known of testing the dis- 

 tance of atoms from one another. In some minds, indeed, 

 there seems to be doubt as to whether such an influence as we 

 are considering exists apart from chemical affinity. 



We may therefore be permitted to notice those cases in which 

 molecular force seems to come into play, and to endeavour to 

 point out the mode in which it acts. 



Attraction of Solids for Liquids. — This heading includes all 

 the cases of so-called capillary attraction, the rise of liquids in 



