

THE 



AMERICAN JOURNAL OF SCIENCE 



[THIRD SERIES.] 



Art. XXXVI. — On Endothermic Reactions effected hy Me- 

 chanical Force ; by M. Carey Lea. (Part First.) 



Ix a preceding paper the effects of pressure on the silver 

 haloids were described. These salts were readily blackened 

 and so gave evidence of partial reduction. That investigation 

 was undertaken with the object of bringing into complete 

 harmony the effects upon these haloids of the different forms 

 of energy. It had been previously shown with respect to all 

 the other forms of energy that a slight impression made upon 

 the haloids caused an effect not visible to the eye but capable 

 of indefinite increase by the application of a reducing agent. 

 Also, it had been shown in the case of mechanical force that a 

 slight application would cause an invisible effect which could 

 be rendered evident by the application of a reducing agent. 

 It seemed to follow almost necessarily that a powerful applica- 

 tion of the same agent would bring about an effect visible to 

 the eye. Experiment proved this to be the case. 



It next appeared worth while to examine whether the same 

 agent, mechanical force, wonld not be capable of bringing 

 about analogous chemical changes in other compounds. For 

 the nature of these changes was something quite different 

 from anything that had been previously described. In Frof. 

 Spring's well known investigation, combination was brought 

 about between substances whose tendency to combine was re- 

 strained by their being in the solid form. This obstacle was 

 removed by subjecting them to great pressure, and the same 

 remark applies to some of the interesting experiments of Dr. 



Am. Jocr. Sci.— Third Series, Vol. XLVI, No. 274.— October, 1893. 

 IT 



