530 Lea— Disruption of the Silver Haloid Molecule, etc. 



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 elec- 

 tricity, 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 phe- 

 nomena 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 sub- 

 stances, 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 re- 

 action. 



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 

 of heat thus generated has anything to do with the reaction. 

 The heat is not perceptible, it is momentary, and it has been 

 elsewhere shown that though moist silver chloride can be 

 broken up by heat, the action is slow even at a temperature of 

 100° C. 



In the case of simple pressure heat certainly plays no part. 

 The material is small in quantity, is folded up in metal, is 

 placed between large and heavy pieces of metal and the pres- 

 sure is applied gradually by means of a screw. Even supposing 

 a slight increase of temperature, it could not exceed one or two 

 degrees and would be momentary. As just remarked, heat 

 does not produce an effect except at about 100° C. and after 

 many hours. 



The powerful affinity which exists between silver and the 

 halogens is well known. That this affinity can be counter- 

 acted and annulled by simple pressure — that the halogen can 

 in part be forced out of the molecule by mechanical means 

 unaided by heat, is remarkable. 



