18 INTRODUCTION. 



homologous with benzol C fi H ft , viz.: toluol C 7 H 8 , xylol 

 C S H 10 , and cumol C 9 H 12 , for instance, the difference is 

 28-29. This conformity is, however, only observed 

 in the case of those bodies which, being homologous 

 according to their empirical composition, are also of 

 an analogous constitution. Conditions dependent upon 

 isomerism can at times entirely withdraw it from 

 observation. "While with ethyl alcohol C 2 H G 0, boiling 

 point 78, normal propyl alcohol, boiling point 97-98, 

 normal butyl alcohol, boiling point 115-116, complete 

 regularity takes place, we observe no regularity in 

 comparing the three following dissimilarly constituted 

 ~iols with each other: 



Ethyl alcohol .... C 2 H 6 boiling point 78, 

 Isopropyl alcohol . . . C 3 H 8 O boiling point 85, 

 Tertiary butyl alcohol . C 4 H I0 boiling point 82. 



Organic bodies undergo the most varied changes 

 when subjected to the action of high heat. Frequently 

 the action is such that hydrogen and oxygen are 

 removed from the body in the form of water, or car- 

 bon and oxygen in the form of carbonic acid, and the 

 other elements of the compound remain united as a 

 new organic body ; for instance: 



C 4 H 6 = C 4 H 4 3 + IPO 



Succinic acid. Succiuic anhydride. 



(C 2 H 3 2 ) 2 Ca = C 3 IFO + C0 3 Ca 



Calcium acetate. Acetone. Calcium carbonate. 



Or one organic body is separated into two new ones 

 under the influence of heat, or there is formed at the 

 same time a larger number of new organic compounds, 

 which, in their turn, are often destroy ed at the moment 

 of their formation, thus giving rise to a complicated 

 mixture of products, generally ending in leaving behind 

 a residue of carbon. These products are different, 

 according as the heat is more or less strong, slower or 

 more rapid. The products of decomposition of bodies 

 free of nitrogen are frequently acid, from the forma- 



