232 



THE GEOLOGIST. 



made portable gas to light him home from the mines at night. 

 About 1809, the improvement had found its way to London, and one 

 side of Pall Mall was illuminated by gas ; and the French, ever on 

 the alert for improvements, lighted parts of Paris with it a few years 

 after. In 1852, four thousand millions of cubic feet were burnt in 

 London alone ! and the quantity of coal to supply this was four 

 hundred and eight thousand tons — ten thousand cubic feet or there- 

 abouts to a ton. Boghead Cannel, I learn from Mr. Binney, pro- 

 duces thirteen thousand to fourteen thousand feet per ton. 



A table of the products obtained during the distillation of coal is 

 given in the useful work we have referred to (p. 567 in vol. 2) ; so 

 that may be consulted for details. Besides the coal-tar from the 

 coke, a number of gases are given off, of which the following are to be 

 found in the gasometer : — 



Carburetted hydrogen — the principal gas we burn : 



Olefiant gas, and some other hydro-carbons : 



Carbonic oxide : Hydrogen : 



And a very little nitrogen, ammonia, and bisulphuret of carbon— 

 the last a substance they do not as yet remove, though, as 

 above said, they might if they would. 



The olefiant gas it is which gives the bright light to gas, for car- 

 buretted hydrogen without it would produce a very dull flame. 



The carbonic acid and sulphuretted hydrogen are separated from 

 the gas by passing it through lime-water. And then there is the 

 combination of stinks (useful in their way no doubt) which make up 

 the " ammoniacal liquor." I can never read the name of this fluid 

 without a shudder. I have fortunately nothing to do with it, and 

 only have time to advert to a few of the products gained by the 

 re-distillation of the coal-tar 



An eminent Scotch professor, at the end of one of his instructive 

 courses, was asked by his students what subjects he would recom- 

 mend them to work at. His reply was characteristic — " Pitch into 

 the residuary phenomena." This is precisely what our chemists 

 have been doing of late years, and that abomination coal-tar has been 

 made to yield us up such precious things, that " we are tempted," say 

 the authors of the book above quoted, " to anticipate the time when 

 within our own borders" — i. e., I suppose, our black borders — " we 

 shall have all the materials for warming, Kghtino;, and cleansing-, 

 which our age demands." 



Tar and coal-naptha are the products gained by distilling this coal- 

 tar ; and when a crude pitch is removed from the tar.an oil remains 

 of great service in lubricating machinery, and the constituents of 

 which, on further distillation, prove to be the same in kind as those 

 in the naptha, although fewer in number. From both, by processes 

 too tedious to go into here, they obtain the celebrated Paraffin (or 

 napthaline, as it should be called), creasote, aniline (from which 

 Mauve and Magenta are made), Benzole, and Toluole, and a number 

 of other -ines and -oles which would not much edify those who are not 

 chemists. 



