176 RESEARCHES ON THE VOLATILE HYDROCARBONS. 
2. Hydrocarbons from Coaltar Naphtha. 
. Benzole Series. 
Name of Substance. Formula. ees a Gates Sean ‘Galen 
HIDE-BOWss theory. lated Boiling-point. 
O° io} eo} 
Benzole, C\. Hy 80.0 93.0 13.0 
Toluole, Cy, Hg 110.8 113.5 8.5 
Xylole, Cys Ayo 139.8 134.0 6.0 
Isocumole, Cys Ay, 169.9 154.5 15.5 
3. Hydrocarbons from Oil of Cumin and Cuminie Acid. 
Calculated Boiling- | Difference between 
Name of Substance. Formula. Haine one point coo i eee 
Cumole, Cys His 151.1 154.5 tga 
Cymole, Cy Hu 179.6 175.0 —4.6 
Cumo-oil of turpentine, Cop Hyg 155.4 160.0 +4.6 
The chief conclusions deduced from the foregoing facts and considerations may be 
briefly summed up as follows : — 
lj. That the boiling-point difference for the addition of C,H, in homologous series 
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 one series 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, corresponding to the elementary difference of C, H,, consid- 
erably smaller than the number 19° of Kopp. 
4. That the formule of Schroder, Léwig, 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, at least in certain 
cases, than if the bulb be placed in the liquid. 
