1 10 Transactions of the 



manufactory was brilliantly illuminated on the occasions of the public 

 rejoicings at the Peace. Such a striking dilference was there between 

 the dingy lamp and the new light, that it began to make real progress 

 in the large commercial towns. London seems to have been the town 

 most uiivvilliug to avail iiself of the new invention, and the cause, no 

 doubt, was that no means of p-irifying it was known, and consequently 

 it was dirty, caused headaches, and spoilt deUcate furniture. This 

 was of little consequence in a manufactory, where there is generally 

 sufficient ventilation to carry off unpleasant vapours, and rarely very 

 delicate organs or fine furniture to suffer from it. But by degrees it 

 crept into use in the metropohs, and, whereas in 1807 Pall Mall alone 

 had the benefit of being lighted, now, without exception, every alley 

 in London is, and no less than eight millions and a half of cubic feet 

 are consumed daily. 



Foreign nations are by degrees adopting its use, and the most im- 

 portant towns on the continent have been or are being supplied with 

 this gas. Such is the brief history of an invention which will never 

 cease to be of use, and which may be applied to many more employ- 

 ments than it is at present. 



I M'ill now turn my attention to the manufacture land products of 

 the distillation of coal. 



The manufacture of coal gas is a branch of industry of great 

 interest and importance in several points of view. The process is one 

 of great simphcity of principle, but requires in practice some delicacy 

 in management to yield a good result. The products of the distil- 

 lation vary in their proportions with the temperature at which the 

 l^rocess iscondncted, the permanent gases becoming more abundant 

 -nith increased heat, but at the same time losing much of their value 

 for the purposes of illumination. It would be a waste of time to 

 describe in detail the manufacture of this gas, which is more or less 

 known to us all, Init I intend to give my attention more esi)ecially to 

 the composition of the gas, and the uses of the bye-products. 



The best coal for this purpose is that which is highly bitumenized, 

 as that which is commonly called cannel-coal. 



The gas after leaving the retorts is purified, and contains, after this 

 operation, melhane (CH,), ethylene (CoH.,), ethene (C.Ho), H, CO, jN", 

 and vapours of volatile licjuid hydro-carbons, besides vapour of CSj. 

 Marsh gas (CH^) is found abundantly in coal mines, and is frequently 

 disengaged from what are technically called " blowers," which are holes 

 in which the gas has been pent up, where probably it has been formed 

 by the action of the heat on the coal. ] t can be artificially prepared 

 by heating Na C2H3O2 Avith Na HO. The gas we barn contains from 

 51 to 41 per cent, of this gas, and consequently it is by no means an 

 unimportant constituent. The colour of its flame is yellow, but it is 

 not to this constituent that the gas owes its luminosity. 



Olefiant gas (C2H4)is the most important compound of the coal gas, 

 though lOU volumes of the latter only contain from 22"G volumes of 

 olefiant gas. The luminosity of this gas is far suiierior to that of 

 marsh gas. It can be prepared by heating alcohol (CaHeO) '^i th HjSO^ : • 



