176 



RESEAKCHES ON THE VOLATILE HYDROCARBONS 





2. Hydrocarbons from Coal-tar Naphtha 



Narae of Substance. 



Benzole, 



Toluole, 



Xylole, 



Isocumole, 



Benzole Series. 



Formula. 



Cm "6 



C„H 8 



C 16 H 10 

 C 18 H 12 



Determined 

 Boiling-point 



80.0 

 110.3 



139.8 

 169.9 



Calculated Boiling- 

 point by Gerhard t's 

 theory. 



93.0 

 113.5 

 134.0 

 154.5 



Difference between 

 Observed and Calcu- 

 lated Boiling-point. 



13.0 

 3.5 



6.0 



10.0 



3. Hydrocarbons from Oil of Cumin and Cuminic Acid. 



Name of Substance. 



Cumole, 

 Cymole, 

 Cumo-oil of turpentine, 



Formula. 



C 18 H 



12 



20 4X H 



CLH 



20 XX W 



Determined 

 Boiling-point. 



151.1 

 179.6 

 155.4 



Calculated Boiling- 

 point by Gerhardt's 

 theory. 



154.5 

 175.0 

 160.0 





Difference between 

 Observed and Calcu- 

 lated Boiling-point. 



+3.4 

 4.6 

 +4.6 





The chief conclusions deduced from the foregoing facts and considerations may be 



2 



in homologous series 



briefly summed up as follows : 



1. That the boiling-point difference for the addition of C 2 H 

 of hydrocarbons is generally 30° C, which is a much larger difference than has been 

 commonly supposed. . 



2. That of the five series 



of hydrocarbons examined, only 



was 



found 



exceptional to the rule just stated, and this presented the boiling-point difference of 

 about 20°, which is but little larger than the number 19°, which Kopp found so com- 

 mon with other classes of substances. 



3. That certain series of derivatives from the benzole series of hydrocarbons present 



boiling-point differences, correspondin 



the 



tary difference of C 2 H 2 , consid 



erably smaller than the number 19° of Kopp. 



4. That the formulas of Schroder, Lowig, and Gerhardt for the calculation of boiling- 

 points, so far as these may be supposed to relate to the hydrocarbons, are incorrect 

 and purely artificial. 



5. That the custom of taking boiling-points with the bulb of the thermometer in 

 the vapor is more liable to lead to an erroneous 



determination 



least in certain 



than if the bulb be placed in the liquid 



