Silver Haloid Molecule hy Mechanical Force. 49 



these silver salts, and differing strikingly from the greenish- 

 black colour assumed by all three silver haloids under simple 

 pressure. 



The fact that the platinum foil remained absolutely un- 

 attacked when the silver haloid was reduced by simple pressure 

 in actual contact with it is interesting, and would seem to 

 show that in the reduction of the silver haloid the halogen is 

 not at any time set free ; but that water, if present, is decom- 

 posed at the same moment, with formation of halogen acid. 



The observations recorded in this paper prove the existence 

 of a perfect uniformity in the action of all kinds of energy on 

 the silver haloids. The balance of the molecule is at once 

 affected by the action of any form of energy. A slight appli- 

 cation produces an effect which, though invisible to the eye, 

 is instantly made evident by the application of a reducing 

 agent. The bonds which unite the atoms have evidently been 

 in some way loosened, so that these molecules break up more 

 easily than those to which energy has not been applied. 

 Consequently, if the substance is submitted to the action of 

 light, heat, or electricity, or if lines are drawn by a glass rod 

 (shearing-stress), or with sulphuric acid (chemism) , a reducing 

 agent blackens the parts so treated before it affects the parts 

 not so treated. This justifies the statement made earlier in 

 this paper, that the phenomena of the latent image and of its 

 development are not exclusively, or even especially, connected 

 with light, as hitherto supposed, but belong to all other forms 

 of energy as well. 



It is therefore true that every form of energy is not only 

 capable of producing an invisible image (that is, of loosening 

 the bonds which unite the atoms), but is also capable, if 

 applied more strongly, of totally disrupting the molecule. 

 This law, in a general form, was proved in previous papers 

 with but a single exception, and that one exception is removed 

 by the observations recorded in this paper. 



As far as observation has gone, silver compounds are the 

 only ones that exhibit this universal sensitiveness. Of other 

 substances some are decomposed by heat, some by electricity 

 or by chemical action, and a few by light. 



It has now been shown, as I believe for the first time, that 

 mechanical force is competent, without the aid of heat, to 

 break up a molecule that owes its existence to an exothermic 

 reaction. 



It is important to distinguish between the two treatments 

 here described. In the case of shearing-stress, force is ex- 

 pended in overcoming friction, and in so doing produces heat. 

 It may be questioned, however, whether the very small amount 



Phil. Mag. S. 5. Vol. 34. No. 206. July 1892. E 



