Chemical Notices : — MM. Berthelot and Berard on Acetylene. 305 



Since, then, the change in U, consequent on any possible 

 change in the resisting forces, is zero, U must be a minimum 

 (the other two possible hypotheses being easily seen to be in- 

 admissible), and the principle is proved for a perfectly elastic 

 body or system of bodies. 



In default of a more general demonstration, it may perhaps, 

 by many persons, be considered self-evident that, cceteris 'pa- 

 ribus, energy must be expended in that way in which there is 

 least opposition to such expenditure, and that, on the other 

 hand, work will be done, cceteris paribus, in that way in which 

 most energy can be expended. And is it not a general law of 

 energy, that the energy expended is a maximum, and the work 

 done a minimum, subject to the laws of transformation of energy, 

 whether general or peculiar to the particular case under con- 

 sideration ? 



1 1 Bamsbury Villas, Liverpool Road, 

 March 3, 1865. 



XLII. Chemical Notices from Foreign Journals. 

 By^. Atkinson, Ph.D., F.C.S. 

 [Continued from vol. xxviii. p. 235.] 



BERTHELOT* has found that when acetylene and iodine are 

 heated together at 100° for fifteen to twenty hours, they 

 combine and form a crystallized iodide which has the formula 

 € 2 H 2 P. 



A saturated solution of hydriodic acid absorbs acetylene slowly, 

 and forms a liquid dihydriodate which is about twice as heavy as 

 water, and is volatile at 182° without special decomposition. Its 

 formation is thus expressed : — 



€ 2 H 2 + 2HI=€ 2 H 4 I 2 . 



It is thus isomeric with iodide of ethylene, than which it is 

 much more stable. 



Both the iodide and the dihydriodate of ethylene yield acety- 

 lene when treated with alcoholic potash. 



Berardf has found that acetylene, when allowed to bubble 

 through an ethereal solution of iodine, is slowly absorbed, and a 

 combination of iodine and acetylene is formed. This compound, 

 however, is more easily obtained when silver-acetylene sus- 

 pended in water is shaken with ethereal solution of iodine until 

 the iodine is no longer decolorized. After distilling off the ether, 

 the residue solidifies, forming a mass of yellowish crystals which 



* Comptes Rendus, vol. lviii. p. 977- 

 t Liebig's Annalen, July 1864. 



