328 HISTORY OF PETROLEUM OR ROCK OIL. 



resented them. The first process results in the formation of vegeta- 

 ble mould, which always retains portions of carbon and hydrogen ; 

 while the incomplete operation of the processes II, III, and IV, gives 

 rise to peat, lignite, brown coal, bituminous coal, and pyroschists, in 

 all of which the proportion of the oxygen is much less than the 

 hydrogen, so that their composition may be approximately repre- 

 sented by mixtures of hydrocarbons with vegetable fibre. The fol- 

 lowing results have been selected from a great number of analyses 

 by various chemists, and are for the most part taken from Bischof s 

 Chemical Geology, (vol. I, cap. XV.) The nitrogen which, in most 

 cases, was included with the oxygen in the analysis, has been disre- 

 garded, and the oxygen and hydrogen, for the sake of comparison, 

 have been calculated for twenty-four equivalents of carbon. 



1. Vegetable fibre or cellulose Cg 4H2 0O2 



2. Wood, mean composition ^2i^\i,-S^\^-\ 



3. Peat, (Vaux) C24H14.4O10 



4. Peat, (Regnault) C24H14.4O9.6 



5. Brown coal, (Schrotter) C24HJ 4.3010-6 



6. BroAvn coal, (Woskresensky) ^'2'^\z^t% 



7. Lignite, (Vaux) ^2411^1.306. 4 



8. Lignite, passing into mineral resin, (Regnault) C24H15O3.3 



9. Bituminous coal, (Regnault) ^2 4H1 ^Og.g 



10. Bituminous coal, (Regnault) ^2J^\q^\-i 



11. Bituminous coal, (Regnault) ^2a^?>-S^\'^ 



12. Bituminous coal, (Regnault) O2 4H8OQ.9 



13. Bituminous coal, (Klihnert and Griiger) C2 4117.401 .3 



14. Bituminous coal, mean composition, (Johnston) C24II9O2-O4 



15. Albert coal, (Wetherell) ^2'^\h-'d^\-^ 



16. Asphalt, Auvergne C2 4Hj^7.7 02.2 



17. Asphalt, Naples C2 i^xi'^^2 



18. Asphalt, Bastennes C24H1 6^0*7 



19. Elastic bitumen, Derbyshire, (Johnston) C24H22O0.3 



20. Bitumen of Idria C2 4Hg 



21. Petroleum and naphtha C2 4H2 4 



In the above table we see the transition from peat and brown coal 

 to lignite, and thence to bituminous coal. Professor Johnston, from 

 his experiments in various coals, including cannel from Wigan, splint 

 coal from Workington, and caking coal from Newcastle, deduced the 

 composition given in 14, in which with C24H9 the oxygen varies from 

 two to four equivalents. It will be seen from a comparison of the 

 infusible Albert coal with the bitumens 16, 17, and 18, how gradual 

 is the transition to the true petroleums and naphthas, from which 

 oxygen is absent. The asphalts also, as will be observed, differ very 

 much in their composition, and though generally much richer in hy- 

 drogen than the bituminous coals, the variety from Naples (17,) which 

 is completely fusible at 140° C, contains less hydrogen and more 

 oxygen than the Albert coal analyzed by Wetherell; while the idria- 

 line or bitumen found with the mercury ores of Idria approaches very 

 nearly in composition to the bituminous coals 11, 12, and 13, with 

 of l^^many asphalts may be said to be isomeric. It is, however, prob- 

 '^ ">se oxygenized bitumens, unlike the coals, are products 



