78 Prof. H. E. Armstrong on the Determination of 



Important confirmation of the value found by Thomsen for 

 x in the equation 



^=-H + CH 3 



is afforded by Longuinine's determinations of the heat of 

 combustion of propyl, isobutyl, amyl and capryl alcohols in 

 the liquid state, which gave as values of x 156400, 156900, 

 and 156200 units ; and especially by Stohmamr's observations 

 on the homologous phenols *. These are given in the fol- 

 lowing Table, the numbers in the third column being each 



Table II. 





/. 



X. 



Phenol, solid 



723659 



726002 



883008 



879758 



880956 



882900 



880441 



1035434 



1037499 



1035638 



1191451 



1354819 



1353750 



1349982 



670780 



824724 



157006 

 156099 

 154954 



156898 

 156782 

 155887 . 2 

 155748 . 2 

 155989 . 2 

 155931 . 3 

 157204 . 4 

 156937 . 4 

 156581 . 4 



153944 









Metacresol, liquid 



Paracresol, liquid , . 





Orthoxylenol, solid 



Metaxy lenol, liquid 





Pseudocumenol, solid 



Carvacrol, liquid 



Thymol, liquid 



„ solid 



P-esorcinol, solid 



Orcinol, solid 



Mean 



156152 







is considerably above the highest of the forty-four differences in Table I. 

 Thomsen himself, however, calls attention to the probable inaccuracy of 

 the number for pseudocumene and mesitylene, the determination being 

 very difficult in the case of bodies so rich in carbon and of such high 

 boiling-point. 



It should here be mentioned that Stohmann, Rodatz and Herzberg 

 {Journ. fur praktische Chemie, 1886, xxxiii. p. 241) have called in ques- 

 tion the number 799350 given by Thomsen. These chemists find 787488 

 units as the heat of combustion of benzene-vapour at 17°, that of liquid 

 benzene at 17° being 779262 units — a value which differs from that given 

 by Berth elot (776000 units) only in the ratio of 100-4 to 100, and is 

 almost identical with the value found — but rejected — by Thomsen in the 

 second of his four sets of determinations of the heat of combustion of 

 benzene. It is perhaps noteworthy that the difference between Stoh- 

 mann's value for benzene and Thomsen's value for toluene, viz. 168192 = 

 955680 — 787488, is very nearly the same as half the difference found by 

 Thomsen to obtain between the heats of combustion of toluene and 

 trimethylbenzene. 



* Journal fur praktische Chemie, 1886, xxxiv. p. 326. 



