158 RESEARCHES ON THE VOLATILE HYDROCARBONS. 
elementary atoms which it contains, without deducting from this sum a constant 
number, as by Schréder’s method. According to Liéwig’s theory, one atom of carbon 
(C) raises the boiling-point 38°4, and one atom of hydrogen (H) lowers it 29°.2; 
these numbers being for carbon nearly two and one half times, and for hydrogen 
nearly three times as great, as those of Schréder. Gerhardt,* in a special paper 
“On the Boiling-point of the Hydrocarbons,” observes that “The boiling-point of the 
hydrocarbons appears to obey a very simple law, according to which it is raised or 
depressed a certain number of degrees, corresponding to the number of equivalents 
of carbon or hydrogen contained in its equivalent.”+ From a comparison of the 
boiling-points and formule of several well-known hydrocarbons, the determinations of 
which were repeated with special care for this purpose, Gerhardt finds that the addi- 
tion of C, to the molecule of an hydrocarbon raises its boiling-point 35°.5, and that 
the addition of H, lowers it 15°. The boiling-point of a body is calculated from these 
numbers by comparing its formula with oil of turpentine, C., H,,, as a standard, the 
boiling-point of which is taken at 160° C. Example: cumole (from cuminic acid) has 
the formula C,,H,.; hence it contains C, less than oil of turpentine ; therefore 35°.5 
must be deducted from 160° (the boiling-point of oil of turpentine), which leaves 
124°.5; but as the cumole contains 2 H, less than oil of turpentine, 15° x 2 = 30° is 
to be added to the above remainder; thus 124°.5-+ 30° = 154°.5, the calculated 
boiling-point of cumole. Gerhardt’s direct determination was 153°, which very nearly 
coincides with his theory. 
It would be foreign from my purpose on the present occasion to consider these 
different hypotheses, or even the empirical law of Kopp, beyond their special relation 
to the boiling-points of the hydrocarbons, and such other series, derivatives from the 
hydrocarbons, as have been made the subjects of my own experiments. Anything 
more than this would be merely speculative. The want of more accurate determina- 
tions of boiling-points as essential to safe and reliable deductions and generalizations 
on this question, has frequently been observed. The need of this will be made 
strikingly apparent by comparison of my results with those of previous observers. 
Indeed, if my determinations may be taken as a criterion, — which, considering the 
nature of the materials operated upon, might not be quite fair, — the inaccuracies of 
the boiling-points which have hitherto been published are probably so numerous, and 
* Annales de Chimie et de Physique, 1845, 3° Série, XIV. 107. 
{ “Il parait que le point d’ébullition des hydrogéne carbonés est soumis 4 une loi fort simple, d’aprés laquelle 
il s’éleverait ou s’abaisserait d’un certain nombre de degrés suivant le nombre des équivalents de carbone ou 
@hydrogéne renfermés dans leur équivalent.” 
