.S7A' ll'/U./AM .S7/;. I/A'. Y.s; F.R.S. 253 



the retort when first charged are to a great extent occluded gases 

 of low illuminating power such as fire-damp or marsh gas, and 

 these should be turned into the heating mains. In the course of 

 half-an-hour these occluded gases, together with the aqueous and 

 other vapours will have left the coal, which is then in the best 

 condition to evolve olefiant gas and other gases rich in carbon, and 

 therefore of high illuminating power. The period during which 

 such illuminating gases arc emitted extends over probably tun 

 hours, after which the retorts should again be connected with the 

 heating gas mains, until the end of the process. By this method 

 of working, the illuminating gas supplied, say in London, from 

 Newcastle coal, would probably exceed 20 candle-power, instead 

 of being 16 as at present, whereby the objectionable effects of gas 

 lighting would be greatly diminished, and there would be, say, an 

 equal volume of heating gas available, consisting for the most 

 part of marsh gas, which although greatly inferior to olefiant gas 

 in illuminating effect would be actually more suitable for heating 

 purposes, because less liable to produce soot in its combustion. 



The total cost of production would not be increased by this 

 separation of the gases, and the price might, with advantage both 

 to the supplier and to the consumer, be so adjusted that the latter, 

 while paying for his illuminating gas an increased price propor- 

 tionate to the increase of illuminating power, would be furnished 

 with heating gas at a greatly reduced cost ; for the heating gas 

 could be reduced in price in a much larger proportion than the 

 illuminating gas need be raised, because it would not require the 

 same purification from sulphur which renders illuminating gas 

 comparatively costly. The enormous increase of consumption 

 would moreover enable the gas companies to reduce prices all 

 round very considerably without interfering with their comfort- 

 able revenues. 



For such large applications of heating gas as to the working of 

 furnaces and boilers, simpler means than the retort can be found 

 for its production. It is now exactly twenty years since I brought 

 out, with my brother, Frederick Siemens, the regenerative gas 

 furnace, which is so largely used in the manufacture of steel, iron, 

 glass, &c., that I need not describe it in detail on this occasion. 

 The effects produced through its introduction into extensive prac- 

 tice are sufficiently apparent to speak for themselves. The glass 



