46 Mr. M. Carey Lea on the Disruption of the 



the observed values, were practically identical with Person's 

 supposed constant of —160°, whereas in the case of the third 

 solvent, sulphuric acid, for which I got a very different value 

 for the temperature of no crystallization, this substance 

 happened to be the very one in which my calculated freezing- 

 points could not be regarded as satisfactory. 



IV. Disruption of the Silver Haloid Molecule by Mechanical 

 Force. By M. Carey Lea*. 



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 t. It was there shown that these 

 substances possessed 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. 



2nd. Light. 



3rd. 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- 



* From an advance proof, communicated by the Author, having- been 

 read before the National Academy, April 1892, by Dr. George F. Barker. 

 t Phil. Mag. April 1891, p. 320. 



