RESEARCHES ON THE VOLATILE HYDROCARBONS. ][,{) 



loss of the substance, by which the quantity 1 1 ad become so much reduced thai I could 

 ill afford further loss. In the case, also, of cymole from oil of cumin, and cumole from 

 cuminic acid, in which the boiling-point difference varies only 1°.5 from the common 

 difference of 30°, the want of perfect .agreement may be fairly 10001111 ted for by the 



fact that the quantity of cumole at command was too simill to admit of continuing the 



process of fractioning far enough to obtain perfect constancy of boiling-point In con- 

 sequence, also, of the quantity being so small, the determination of the boiling-point of 

 cumole is less reliable, as this had to be conducted in a test-tube. It came into full 

 ebullition at 148°.4, the temperature rising gradually to 15T.6 (observed temperature ), 

 at which latter temperature it had distilled nearly to dryness. The distillation occu- 

 pied thirteen minutes in passing over the range of three degrees. The average of* the 

 extremes, with the usual corrections for pressure, &c, was taken for the boiling-point 

 Abel,* wdio probably operated on a larger quantity, found the boiling-point of cumole 

 to be 148°. It does not appear that he applied the corrections for pressure ami the 

 upper column of mercury. I do not doubt that the true boiling-point of this body 

 will be found to be 150°, which would establish the difference of 30° between it and 



cymole. 



I would here remark that this difference of 30° for the addition of C 2 1 r, was first 

 observed while engaged in fractioning Pennsylvania petroleum, and the oil from 

 Albert coal, — substances the most difficult to separate, on account of the presence in 

 each of two parallel series of constituents, whose boiling-points lie so mar together. 



As no one had preceded me in the investigation of these substance-, my mind was 

 as far as possible unbiased as to the boiling-points of the constituents of these mix- 

 tures. I was, however, aware of the beautiful relation between elementary constitu 

 tion and boiling-point which Kopp had discovered, and familiar with the fact that the 

 more recent investigations had shown the boiling-point difference among homologous 

 hydrocarbons to be about 22°.5. If there was any one thing which more than another 

 tended to bias me, it was the recent work of Churchf on the boiling-points in the 

 benzole series, in which he made the boiling-point difference invariably l2 3 and a frac- 

 tion, a number varying but 3° from the theory of Kopp. Soon after the publication 

 of Church's results, however, Kopp J accepted the number 22.5 as about the boiling- 

 point difference in this series, therefore regarding it as one of the exceptional series in 

 which the boiling-point difference is greater than 19°. The work of Church had cer- 



* 



t 



Annalen der Chemie und Pharmacie, 1847, LXIIL 308 



X Annalen der Chemie und Pharmacie, 1855, XCVI. 29. 



VOL. IX 26 



