370 Br. A. Ransome on some of the 



The crystallization of camphor along the striae of matter left 

 by a cloth on a glass rod, or the formation of ice-crystals on a 

 window-pane in the track of the cloth used in cleaning it, are fa- 

 miliar instances of similar influences at work. 



Most catalytic agents probably owe some part of their power 

 to this influence of points ; many of them are employed in the 

 form of powder ; and even pounded glass or earthenware have 

 been shown to possess catalytic powers. It is also worthy of 

 notice that the most energetic catalytes are those in which the 

 active element is not only finely divided, but the particles are so 

 separated from one another that they can act alone and without 

 any perturbing influence from others of the same kind. Thus 

 ordinary wood-charcoal, although it will act as a catalyte, is in- 

 ferior in power to animal charcoal, in which the molecules of 

 carbon are separated from one another by earthy matter ; and 

 spongy platinum is similarly superior to platinum -black. 



Bodies also which in the colloidal form are catalytes, from 

 possessing the property of penetrability and allowing close con- 

 tact, lose their power when by heat or any other agency they 

 are coagulated or pectized, and the molecules are thus brought 

 closer together. It seems probable that in some medicines, as 

 grey, Dover's, or James's powders, the activity of the drug is in- 

 creased by the presence of an inert body with which it is incor- 

 porated. The therapeutic value of the fine division of medicine 

 is a subject still requiring investigation. 



Friction. — It is a question how far the coefficient of friction 

 (/n) may depend upon the molecular as well as the cohesive at- 

 tractions of the points which form the rough surfaces of the 

 bodies in contact. It may perhaps be permitted to surmise that 

 when these projecting points are brought together, their mole- 

 cular affinities will have some influence upon the result. 



3. The Low Chemical Affinity of a Catalyte. 



When it is considered that the molecular forces exerted by a 

 catalyte can only be employed when the substances to be acted 

 upon are brought into very close contact with it (so close that if 

 these substances had strong chemical affinities for one another 

 they would certainly combine), and when, further, it is considered 

 that if the catalyte united chemically with other material it would 



(and probably other substances) radiate more heat than when smooth. But 

 the points which these surfaces present are not the cause of the increase of 

 radiation ; this depends rather upon the diminution of density of the sur- 

 faces and their state of greater subdivision. According to Professor Mag- 

 nus, " in consequence of the roughening of the surface, the amplitudes of 

 the heat-oscillations are altered, but not their rate." (Professor Dana in 

 Silliman's Journal, vol. iv.) 



