416 Dr. C. R. A. Wright on the Relations between 



to the true values of 2SF 100 obtained by means of the above cal- 

 culations from the heats of combustion of the substances ex- 

 amined ; and further, by this means the values of 2SF 100 may 

 be calculated for substances of which the heat of combustion 

 cannot be determined at all, even approximately. The data for 

 such corrections and calculations are as yet extant in only very 

 few instances ; but it is to be hoped that before long the study 

 of thermo-chemistry will be further advanced, so that all sub- 

 stances, and not merely a few organic products, may be thus 

 examined. It may perchance be found convenient to alter or 

 modify the standard adopted for the calculations of the values of 

 2SF 100 (vaporous state at 100° and 763 millims., the constituent 

 elements being all at the same temperature, gaseous save in the 

 case of carbon, and occupying jointly the same bulk as the re- 

 sultant vapour) . The object of the present essay is not so much 

 to fix an absolute standard for reduction, as to point out the way 

 for such and to draw attention to some of the results flowing 

 from such calculations. 



25. It may here be noticed that the character of some of the 

 values of H 100 deduced above for various classes of reactions differs 

 from those deduced by Julius Thomsen (Deut. Chem. Ges. Berichte, 

 vol. ii. p. 482) from the heats of combustion calculated by Her- 

 mann (ibid. vol. i. p. 18), on the supposition that the materials 

 and products of combustion are all gaseous at 15°, a correction 

 being made for volume-alterations. Thus, whilst Thomsen recog- 

 nized that heat is usually (not invariably) absorbed during the 

 formation of a compound ether from an acid and an alcohol, he 

 concluded that the heat-disturbance is imperceptible in the for- 

 mation of an olefine and water from an alcohol, of an ether 

 and water from an alcohol, and of carbon oxide and water from 

 formic oxide. As regards this latter, however, Thomsen subse- 

 quently showed (Deut. Chem. Ges. Berichte, vol. v. p. 957) that 

 heat is actually absorbed during the decomposition, and is conse- 

 quently evolved during the synthesis of the acid from carbon 

 oxide and water — this result being arrived at by means of an 

 actual accurate determination of the heat of combustion of formic 

 acid (the one used above, viz. 1'308), and not from a value in- 

 ferred by analogy from Hermann's reduced value for higher 

 homologous acids ; both of which results, however, negative the 

 conclusion drawn by Berthelot from Favre and Silbermann's 

 rough approximation, that heat is developed during the decom- 

 position (Comptes Rendus, Oct. 10, 1864 ; Ann.de Chim. etdePhys. 

 [4] vol. xviii. p. 24), and render unnecessary in this instance 

 Oppenheinr's ingenious speculations as to the cause of such de- 

 velopments of heat (Bull. Soc. Chim. Paris [2] vol. ii. p. 419). 



26. Some points of considerable interest are revealed by the 



