RESEARCHES ON THE VOLATILE HYDROCARBONS. 137 



to the increment of boiling-point corresponding to the addition of C 2 If 2 in homologous 

 series. It was therefore deemed advisable to extend the inquiry so as to include the 

 naphthas from coal- and wood-tars, and the oil of cumin. And there are still other 

 mixtures of hydrocarbons, that have been made the subjects of previous research, 

 which must yet be brought into the work, in order to clear up, in a satisfactory man- 

 ner, the confusion and obscurity that seem to exist in our publications regarding some 

 questions relating to the different series of this class of bodies. 



This digression from my original plan, having caused much additional labor, has 

 necessarily delayed publication longer than was desirable, until now the results of 

 more than three years of work have accumulated. In this connection 1 may remark, 

 so far as regards petroleum, that I had nearly completed the fractional separations 

 except of the bodies of high boiling-point — so long ago as June, 1862, having been 

 for a long time occupied with this work before the appearance, in that month, of the 

 first memoir of Pelouze and Cahours on the same subject. At that time my work 

 was considerably in advance of theirs, and their results differed widely from mine in 

 some important particulars ; yet after the publication of their memoir I felt reconciled 

 to a continuance of the delay which had been caused by the change of plan above 

 mentioned, considering it due to these chemists that they should have time to com- 

 plete the publication of the results of their investigations before I should publish 

 mine. Similar remarks might be made respecting the first publication of Schorlem- 

 mer, which appeared soon after, on the products of distillation of cannel coal ; this 

 substance being so closely analogous to the Albert coal (upon the products of which 

 I had at that time been long engaged) as to induce the belief that, under the same 

 circumstances, either would afford the same products. 



I. 



On the Volatile Hydrocarbons from Coal-tar Naphtha, Oil of Cumin, and Cuminic Acid. 



PART I. 



HYDROCARBONS FROM COAL-TAR NAPHTHA, 



• In presenting the results of a re-examination of a series of substances upon which 

 so much labor had already been bestowed, and upon the nature and properties of 

 which so little doubt has seemed to exist, it may confer an interest on the subject to 

 state briefly some of the more important results and conclusions that previous inves- 

 tigators have arrived at in the study of these substances. 

 vol. ix. 22 



