by Contact of Liquids with Powdered Silica Sfc. 315 



tact, the ensuing state of steady charge and the subsequent 

 discharge ; and may be further compared with the effects of 

 approach and withdrawal of magnets and their armatures, 

 and with the commencement ^nd cessation of electric currents 

 by magnetoelectric and dynamoelectric induction. All these 

 five actions are reversible ones, attended by molecular change, 

 disturbance of the aether, and transference of radiant energy 

 at the moments of commencement and termination, with a 

 new state of molecular balance but no external dynamical 

 effect during the intervening statical period, and by an 

 undoing of the first dynamical effect by the second one in 

 each class of cases. They are all evidently based upon similar 

 mechanical princio^s of molecular motion. 



As the quantity of heat evolved per given weight of 

 potassium cyanide in experiments 52, 53, 54, 57 was larger 

 the more dilute the solution, the amount of loss of velocity, 

 and the actual velocity of the molecules of that salt were 

 greater the more dilute the solution. The latter conclusion 

 agrees with the observation that the voltaic electromotive 

 force of a dissolved substance is usually increased by dilution 

 (see " A General Relation of Electromotive Force to Equiva- 

 lent Volume and Molecular Velocity of Substances," Proc. 

 Birm. Phil. Soc. 1892, vol. viii. pp. 63-138). 



In proportion as the amount of heat evolved is greater, the 

 degree of " adhesion " is stronger and partakes more of the 

 character of ordinary chemical union. Each particle of the 

 powder " adheres" both to the solvent and to the dissolved 

 substance probably in all cases, but in each case apparently 

 in different proportions [ibid. 1894, vol. ix. pp. 1-24) . If the 

 powder " adheres " to a larger proportion of the dissolved 

 substance than it does to that of the solvent, the " adhering " 

 film of liquid is a more concentrated solution than the re- 

 mainder, but if it "adheres" to a smaller one the opposite 

 effect occurs ; but in either case chemical analysis of the 

 separate portion of liquid reveals the change and affords 

 data for comparison with the alterations of temperature, total 

 amount of heat, &c. 



The easily formed anticipation that the amount of rise of 

 temperature produced by a given weight of silica increased 

 with the degree of smallness of the particles was verified by 

 actual experiment. Thus the rise produced by 100 grains 

 weight, consisting of 1037 particles of coarse sand, by im- 

 mersion in 50 centim. of a 10-per-cent. solution of potassium 

 cyanide, was only '03 C. degree, whilst that produced by the 

 same weight of the finest precipitated silica, after washing 

 and heating to redness, was *82 C. degree {see Experiments 



