1879.] Native Bitumens and the Pitch Lake of Trinidad. 231 
by the important facts that unlike many of the bitumens they are 
not liquid at ordinary temperatures, and unlike all the solid bitu- 
mens, are incapable of assuming the liquid state on the applica- 
tion of heat. The coals partake in a large degree of the nature 
of their chief constituent element, carbon, the most thoroughly 
solid substance known, distinguishing, as we should, solidity from 
density. In their entire insolubility, again, the coals are strongly 
contrasted with the bitumens, the latter class being all more or 
less soluble in liquids like benzole, sulphide of carbon, oil of tur- 
pentine and ether; and the less fluid bitumens, as asphalt, dis- 
solving in the more fluid, naphtha-like, varieties. 
Notwithstanding the general distinctness of these two great 
classes of native hydrocarbons, there is a point where they are not 
easily separated. Among the bitumens there are different degrees of 
fusibility and solubility, and a concomitant variation of the 
hydrogen ratio, presenting a regular gradation as we pass from 
naphtha with the maximum solubility and fusibility, and the 
largest proportion of hydrogen, through petroleum, mineral tar, 
and the various asphalts to idrialite, which, having the composi- 
- tion of bituminous coal, is fusible with difficulty, and only slightly 
soluble. From idrialite the passage is easy to true bituminous 
coal, and from this, as is well known, to anthracite. So that, as 
Dr. T. Sterry Hunt has stated it, “ Anthracite or nearly pure car- 
bon, on the one hand, and petroleum and naphtha, or carbon with 
a maximum of hydrogen, on the other, represent the two extremes 
of a series of which bituminous coals and asphalts are interme- 
diate terms.” 
Following is a list of the more important members of this 
series, with their formulas, which have been calculated for twenty- 
four equivalents of carbon, to compare with the chief constituent 
of wood, cellulose: 
Cellulose...... Dele och eye eetresebosere Cas Hy On 
Naphtha 
a GHH 
nos O EPR EDE BRIE 1 Ma 
Mineral Tar. wo len scons si ewan wow nenies has Bene bus H 
varies from C, H O 
Asphalt a5. iassa ‘ f to GC HO 
cette tt PRO, tC a er 
Cy Hie 
ent i varies from Cy Ho Os 
ey bee eae Ohi eas to Cy H, 0 
: varies from Cy H, O 
Piathracite 666 bh os ee ee | è CH, O. 
