ON THE PHENOMENA AND THEORIES OF SOLUTION. 469^ 



volume, of specific heat, and thermal changes, positive or negative. The 

 same may be said of the act of diluting this solution. More water (or 

 more salt) being added, similar physical phenomena are exhibited ; and it 

 is important to notice, as already stated more than once, these changes 

 are all continuous one with another, the specific volume of the added 

 water constantly tending towards that of water itself. The conclusion 

 «eems inevitable that chemical combination is not to be distinguished by 

 any absolute criterion from mere physical or mechanical aggregation, and 

 it seems not improbable that it may ultimately turn out tha^t chemical 

 combination differs from mechanical combination, called cohesion or adhe- 

 sion, only in the fact that the atoms or molecules of the bodies concerned 

 ■come relatively closer together, and the consequent loss of energy is 

 greater. 



The researches of Miiller-Brzbach, published in a long series of papers 

 {especially ' Ber.' 1880, p. 1658, and 1881, p. 217), strongly support such a 

 view. He has shown by numerous examples that in similarly constituted 

 solid bodies those are the most stable in the formation of which the 

 greatest contraction occurs. Thus when lead replaces silver, or potassium 

 replaces sodium in the nitrate, or when chlorine replaces bromine or 

 iodine in combination with another element, contraction occurs. And in 

 ■general, contraction is observed when an element of reputed strong 

 affinity (as indicated by the results of thermo-chemical experiment) takes 

 the place of one of reputed smaller affinity. This is only an extension of 

 what has already been observed in the combination of water with salts, 

 and which in all probability applies generally in the comparison of atomic 

 ■combination as distinguished from so-called molecular combination. 



We are in the habit of using the word ' attraction ' in a somewhat 

 indefinite and unsatisfactory manner in referring to the hypothetical 

 cause of the union of atoms or molecules. "We do not know what this 

 "thing is which is called chemical affinity or attraction. There can be 

 little doubt, however, that it is connected intimately with atomic or 

 molecular motion. It does not require a great stretch of imagination to 

 •conceive that combination occurs most readily and intimately between 

 those atoms or molecules whose motions are nearly alike. And confining 

 our attention to the phenomena now under discussion, it seems not 

 improbable that this may be the explanation of the selective action of 

 solvents, and the disposition so often shown for like to dissolve in like. 

 It may also, perhaps, go some way towards explaining the great amount 

 of heat evolved and the great contraction which ensues when many 

 anhydrous salts are brought into contact with water, as compared with 

 the effects of dissolving the same salts when in the hydrated state. 



On the Ex'ploration of the Raygill Fissure in Lothersclale, 

 Yorkshire. By James W. Davis, F.G.S. 



[A communication ordered by the General Committee to be printed in extemo 



among the Keports.] 



The Raygill Fissure, in the mountain limestone in Lothersdale, about 

 five miles south-east of Skipton, was investigated to some extent by 

 a Committee of the Association, and a report was presented by 



