62 



III. The Cyclo-Paraffins (Polymethylenes) or so-called 



Naphthenes, or ring, saturated hydrocarbons, some 3 

 times considered as hydrogenated aromatic com- 

 pounds, though not quite correctly so, for they range 

 from 3-membered (Trimethylenes) up to 8 or 9-mem- 

 bered Carbon rings. 



IV. The Aromatic Hydrocarbons of the Benzene series. 

 V. The Olefines of the Ethylene series, with one double 



bond in the molecule. 

 VI. The Di-Olefines with two double bonds. 



These latter unsaturated hydrocarbons are found in natural 

 mineral oils in only small quantities, but in oils obtained by the 

 distillation of shales always in abundance. This is due to the 

 occurrence of " cracking," i.e., the splitting the larger molecules 

 undergo at high temperatures into smaller fragmentary molecules. 

 The stability of the hydrocarbon molecule at high temperatures is 

 roughly inversely proportional to the molecular mass. This 

 phenomenon of cracking was first adequately investigated in the 

 classic research of Thorpe and Young. (R.S. Proc. , Vol. 19, p. 

 87, 1871), when by repeated redistillation at high temperatures 

 under pressure pure paraffin wax was made to yield low-boiling 

 liquid hydrocarbons, roughly half and half olefines and paraffins. 

 Heusser (Berichte, Vol. 30, p. 2744), in a direct analysis of Scotch 

 Shale oil, records 44 per cent, of Paraffins, 10 per cent. Naphthenes, 

 7 per cent. Aromatics and 39 per cent. Olefines. Pennsylvanian 

 oils consist largely of paraffins, the Caucasian oils contain up to 

 80 per cent, naphthenes, while Borneo oils contain a fair propor- 

 tion of aromatic hydrocarbons, a circumstance which makes them 

 particularly valuable as the source of the basic-material of various 

 high-explosives. This variety of composition may be ascribed in 

 part to the different mother substances of the oil and in part to the 

 diversity of local conditions of temperature and pressure under 

 which the oils were conceivably naturally derived by distillation 

 from the original bituminous sediments. 



T he chief theories of the origin of mineral oil and its im- 

 mediate source, the bituminous shales, may be now briefly out- 

 lined. Perhaps the oldest theory on record is that published in 

 1791. bv Balthasar Hacquet, an Austrian physician of French 

 extraction, who for 23 years was professor of natural science in 

 Lemberg and Cracow. It anticipates the generally accepted 

 modern theory of Engler in concluding that the Galician oil 

 originated by the dissolution of marine animals in sea water, oil 

 and salt therefore being naturally in close vicinity. This theory 

 probably displeased his contemporary, the Polish clergyman. 

 Chr. Kluk, a noted mineralogist and zoologist, who in 1781 dis- 

 missed the possib ; lity of an organic origin and developed a theory 

 on a purelv biblical basis ; that the earth soon after the creation 

 of man abounded in fats making life pleasant, which on the fall 



