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



With respect to these corrections, it is evident that the expe- 

 rimental difficulties in the determination of the exact values of 

 Hj are so considerable that a larger number of determinations 

 than was usually made by Favre and Silbermann is required in 

 each instance before a mean value can be obtained on which per- 

 fect reliance can be placed. These experimental errors do not 

 seem materially to affect the nature of a curve drawn, as by 

 Favre and Silbermann, to indicate the rise in value of Hj as an 

 homologous series is ascended ; but they become far more per- 

 ceptible in the values 2SF ]00 , every such error being there mul- 

 tiplied by 28. As shown in § 24, however, a means is afforded 

 of correcting in future these first approximations to the true 

 values of 28F 100 by observing the heat- disturbance occurring 

 during definite chemical reactions under known conditions of 

 temperature, pressure, and physical state. 



17. The reduced affinity-values obtained as above afford the 

 means of calculating the amount of heat-disturbance (evolution 

 or absorption) in any given reaction, the materials and products 

 being all supposed to be gaseous, and at the uniform tempera- 

 ture 100° and pressure 760 millims. The heat evolved during 

 such a reaction (H 100 ) must necessarily be given by the equation 



H 100 =2(F p )-2(FJ + A 7 ; 



where S(F p ) and 2(F TO ) are the algebraic sums of the affinity- 

 values of the products and materials respectively, and H 7 the 

 heat-evolution which corresponds to the amount of contraction 

 in volume that takes place during the reaction ; for S(F TO ) de- 

 notes the heat that would be absorbed were the materials all 

 resolved into their constituent elements, and X(F p ) the heat de- 

 veloped by the recombination of these elements to form the pro- 

 ducts, whilst h 7 is the correction for volume-alteration, being 

 equal to 



m x 0-372, 



where m is the number of metropneums (at 100° and 760 mil- 

 lims.) of contraction that take place during the reaction (§ 13). 



18. Thus the formation of an olefine and water from an 

 alcohol takes place in accordance with the general equation 



O H 2w+2 O = C n H 2ra + H 2 O 5 



for every metrogramme of alcohol — 2 metropneums contraction 

 take place during the reaction, or m= — 2 ; hence 



H M0 =S(P F )-2(PJ-0-744 



=a+b—c— 0*744; 



where a is the affinity- value of the define formed, b that of water, 

 and c that of the alcohol used. Thus ; — 



