Endothermic Decompositions obtained by Pressure. 31 



Apart from the comparison of the specific gravity of the 

 ethyl acetate before mixing and after fractionation, a proof 

 of the purity of this substance is afforded by the agreement 

 between the specific gravities of the two samples, since, if the 

 separation had been incomplete, one would have been con- 

 taminated with methyl acetate, the other with propyl 

 acetate. 



III. On Endothermic Decompositions obtained by Pressure. 

 (Second Part.) Transformations of Energy by Shearing 

 Stress. By M. Cabey Lea*. 



OF the relations which exist between two forms of energy, 

 mechanical and chemical, very little, if anything, is 

 known. In the second volume of his Lehrbuch Ostwald 

 remarks that as to these relations a almost nothing " is 

 known f. 



There are certain familiar cases in which mechanical 

 energy may seem at first sight to be converted into chemical 

 energy. The fulminates, iodimide, and other substances ex- 

 plode by shock. But it is hardly necessary to remark that 

 all such reactions are exothermic, and need an external im- 

 pulse only to start them — if this impulse were not needed 

 such compounds could not exist at all. Were such reactions 

 taken as true transformations of energy, an absence of due 

 relation between cause and effect would be involved ; for 

 the shock that suffices to explode a grain of fulminate will 

 equally explode a ton, and the faint spark that will explode a 

 grain of gunpowder w T ill also explode a magazine. 



Present opinion holds undoubtedly that no true transfor- 

 mation of mechanical into chemical energy is known. Most 

 text-books do not consider the question at all. But Dr. 

 Horstmann, in the volume of theoretical chemistry which 

 forms part of the last German edition of Graham-Otto's 

 ' Chemistry/ discusses the matter. His views are so much to 

 the point that I shall translate a few sentences, putting in 

 italics the statements to which I would specially refer. 



" We must consequently admit that through a rough me- 

 chanical attack the molecular structure of certain chemical 

 compounds can be disrupted and destroyed. This will cer- 

 tainly be possible only for compounds in whose molecules the 

 arrangement of the atoms does not correspond to a stable 



* Communicated by the Author. 



t " Anderseits ist von dem Yerhaltniss zwischen mechanischer und 

 chemischer Energie fast nichts bekannt." A few lines below this remark 

 is repeated with emphasis. Lehrbuch, 2nd German ed. vol. ii. p. 12. 



