Affinity and Dissected (Structural) Formula. 



425 



in point is afforded by amylic alcohol and amylic ether (§ 35), 

 where the result of one hydroxylicand four hydrocarbonous me- 

 thylations gives a positive increase in boiling-point, but a nega- 

 tive one in affinity-value. 



Similarly, when certain alcohols and their compound ethers 

 are compared, the same kind of result follows. Thus with me- 

 thylic alcohol and methyl formate; the latter may be regarded 

 as derived from the former by the sum of two successive opera- 

 tions, viz. : — 



CH 3 O CH 3 ^ H y drox y lic metn y lation - 

 CH 3 '. . COH } Replacement of H 2 by 0. 



The first gives rise to heat-absorption and corresponding lower- 

 ing of boiling-point, the second to heat-evolution and rise of 

 boiling-point ; but the algebraic sum of the changes in affinity- 

 value is +, and that of boiling-point — . 



Substance. 



Affinity-value. 



Boiling-point. 





aw} Diff - =+ 14 - 6 



11} Diff. =-32 







38. The phenomena of isomerism and polymerism appear 

 also to be subject to the influence of the above thermal rule, a 

 polymeride or isomeride of higher boiling-point having uniformly 

 a higher affinity-value than one of lower boiling-point; i. e. if 

 an operation be performed upon a given substance such that it 

 becomes converted into an isomeric or polymeric body of higher 

 boiling-point, heat is evolved during the operation, and vice versa. 



Thus:— 



Substance. 



Affinity-value. 



Boiling-point. 





i£o} Diff - =+ 501 



— v'O yv«? | i r..Q 



+ !„'* Diff =+36 

 1 129-1 Diff. =+82-8 

 + JJJ4 Diff. =+67-8 



115} Diff- =+59 



T 1 ??-' Diff. = + 135? 

 X,S Diff. = + 125 

 +1% Diff. = + U5 

 +395 Diff. =+120 



Methyl valerate 



Ethylene 







Tetraraylene 





Methyl formate 



,^} Diff. =+42-0 



,^V Diff. =+84 

 lis} Diff. =+82 

 ,£]■ Diff. =+81 



Ethyl acetate 



Butyric acid 



Methyl butyrate . . . 

 Valeric acid 





If the uncorrected value for methyl butyrate and valerate be 



