FORMATION OF COAL AND CARBONACEOUS MINERALS. 129 



principal product, and forms the basis of the West European 

 manufacture of mineral oils and paraffin. The otlier products of 

 the destructive distillation of such more recent fossils possess 

 veiy little or no value, except in the case of some very dense, 

 coal-like, brown coals, which furnish good coke and good gas but 

 no mineral oil." 



These quotations shew the genex^al drift of opinion amongst 

 those intimately connected with the subject of distillation, as I 

 have also been more or less for thirty years. There is a radical 

 dift'erence in the substances submitted to retorting, and although 

 the fatty hydrocarbons are more or less converted into gas and 

 aromatic hydrocarbons by a Iiigh temperature, the transformation 

 is always incomplete, and I believe that the difference in products 

 ai'ises chiefly from the original diflerences of the vegetation of which 

 the coal or shale was formed. Of the various mineral fuels, some, as 

 anthracite, and splint and cherry coals, are never distilled, the 

 products being of no value. Cokeing coals (in conti'adistinction to 

 gas coals which are used for making both gas and coke) are 

 distilled for the sake of the coke, and a few years since it was 

 anticipated that great results would be obtained by the use of 

 Simon Carves and other improved ovens by which the tar could 

 be collected, but valuable aromatic hydrocarbons were present in 

 such small proportion that the anticipations were not realised. 

 Bituminous gas coal yields tar rich in benzine, anthracene, and 

 other valuable aromatic hydrocarbons and practically none of the 

 fatty series, and tar distillers object to the use of shale along 

 with it, as they introduce these. 



Cannel used alone in gas making, as in Edinburgh and 

 Glasgow, gives a tar yielding less benzine and its homologues 

 than that from bituminous coal, and these are mixed with a 

 noteable pi'oportion of fatty hydrocarbons. From this tar 

 olefins and paraflins boiling from 20° to 100° C are obtainable, 

 and of the liquid obtained at the boiling point of benzine, only 

 about two-thirds consist of that substance which crystalises out 

 when the mixture is placed in ice and salt. On distilling cannel 

 tar only about ten per cent, of oils are obtained which are lighter 

 than water, about thii'ty-tive per cent, on the tar being heavier, 

 and although the lower fractions contain noteable quantities of 

 fatty hydrocarbons these gradually decrease until the heavy pitch 

 oil contains mere traces of paraffins. I speak here of the low 

 heats used in gas making thirty years since, with the high heats 

 employed now-a-days, the quantity of light hydrocarbons is much 

 smaller, not above four to live per cent. On the other hand 

 cannel has been little used for low temperature work, (except 

 Leeswood cannel (which was what we would call here kerosene 

 shale), although the amount of volatile hydrocarbons it contains 

 ranges from forty to forty-five per cent., and even higher in Scotch 

 cannels, whei'e shales yielding thirteen per cent, of oil are worked. 

 J 



