POROSITY OF .MATTER. 41 



without at all increasing the bulk of the fluid. All the 

 solid matter of the salt must, in these cases, it would 

 appear, go to fill up the interstitial spaces which we 

 suppose to exist in the liquid.* 



The conditions which regulate the solubility of 

 bodies, and the power of solution, regarded either as a 

 mechanical or a chemical process, are very obscure. 

 We might be led to suppose, that those bodies possess- 

 ing the largest amount of unoccupied space were capable 

 of holding the greatest quantity of soluble matter dis- 

 solved. This, however, is far from being the case, the 

 denser fluids generally having the greatest solvent 

 power. 



The peculiar manner in which hydrogen gas appears 

 to dissolve solid substances, as iron, potassium, sodium, 

 sulphur, phosphorus, selenium, and arsenic, may be ex- 

 plained by regarding the results as a manifestation 

 of the powers of chemical affinity over the forms of 

 bodies. In like manner, the solution of salt in water, 

 or the mixture of alcohol in that fluid, may be viewed as 

 chemical phenomena, although usually considered as 

 simple cases of solution or mixture : alterations of tempera- 

 ture and other physical changes taking place in either. If 

 two masses of metal, either tin and copper, for example, 

 are melted and combined, the united mass will not 

 equal the bulk of the two masses. If a pint measure of 

 oil of vitriol and an equal quantity of water are mixed 

 together, the combined fluids will not fill a two pint 

 measure, f 



* This was first proved by the researches of Dr. Dalton : the 

 subject will be again alluded to under the consideration of atomic 

 volumes. 



f These peculiar phenomena may be studied advantageously in 

 the works of most of the eminent European chemists. In our 

 own language the reader is referred to Dr. Thompson's Outline of 

 fhe Sciences of Heat and Electricity, '2nd edition; Brande's 

 Manual of Chcmixtry-^Art. Specif c Heat ; Graham's Elements of 

 Chemistry ; and Daniell's Introduction to the Study of Chemical 

 Philosophy. 



