232 
THE GEOLOGIST. 
made portable gas to light him home from the mines at night. 
About 1^09, 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, fom- thousand millions of cubic feet were burnt in 
Loudon 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 fom'teen thousand feet per ton. 
A table of the products obtained dm^ing 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 hydi'ogen — the principal gas we burn : 
Olefiant gas, and some other hydro-carbons : 
Carbonic oxide : Hydrogen : 
And a veiy httle nitrogen, aromouia, 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 hriglit light to gas, for car- 
buretted hydrogen without it would produce a very dull flame. 
The carbonic acid and sulphuretted hydi'ogen 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, lighting, 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 -mes and -oles which would not much edify those who are not 
chemists. 
