Lea — Disruption of the Silver Haloid Molecule, etc. 527 



Art. LX YII. — Disruption of the Silver Haloid Molecule by 

 Mechanical Force) by M. Carey Lea. 



[Read before the National Academy, April, 1892, by Dr. George F. Barker.] 



In a paper published about a year ago on the subject of 

 allotropic silver there was included an investigation into the 

 action of the different forms of energy upon silver chloride 

 and bromide.* It was there shown that these substances pos- 

 sessed an equilibrium so singularly balanced as to be affected 

 by the slightest action of any form of energy. Such action 

 produced a change which though it might be wholly invisible 

 yet caused the breaking up of the haloid when subsequently 

 placed in contact with a reducing agent. The forms of energy 

 with which this effect was observed are : 



1st. Heat. 



2d. Light. 



3d. Mechanical force. 



4th. Electricity (high tension spark). 



5th. Chemism. 



It follows therefore that it is not light only that is capable 

 of producing an invisible image but that this power belongs 

 alike to all forms of energy. So that a slight impulse from 

 any one of the forces just mentioned brings about a change in 

 the equilibrium of such a nature that the molecule is more 

 easily broken up by a reducing agent. 



As respects four out of these five forms of energy, it was 

 further shown that when made to act more strongly, they were 

 able of themselves to disrupt the molecule without external 

 aid. One form alone of energy, mechanical force, made an 

 apparent exception to this general rule. The other four, when 

 applied to a moderate extent, produced a latent image, applied 

 more strongly they broke up the molecule. 



The object of the present paper is to prove that this excep- 

 tion does not exist, and that as all forms of energy have been 

 shown in the previous papers of this series to be capable of 

 impressing an invisible image, so also with stronger manifesta- 

 tions, any form of energy is capable of disrupting the mole- 

 cule. 



I was able to show many jears ago that mechanical force 

 could produce a latent image. Lines drawn with a glass rod 

 on a sensitive surface could be rendered visible by develop- 

 ment in the same way as impressions of light. An embossed 

 card pressed on a sensitive film left an invisible image which 



* This Journal, April, 1891. 



