163 Royal Institution : — 



the indication of the galvanometer ; strike the key sharply again, 

 readjust resistances ; and so on, until the balance is nearly attained. 

 He will go on repeating the process, but holding the key down 

 rather longer each time. At the last he will press the key gently 

 down, hold it pressed firmly for something less than a second of 

 time, and let it rise again ; and if the spot of light reflected from the 

 mirror of the galvanometer does not move sensibly, the resistances 

 are as accurately balanced as he can get them. 



ROYAL INSTITUTION OF GREAT BRITAIN. 



June 20, 1862.— The Duke of Northumberland, K.G., F.R.S., 



President, in the Chair. 



" On Gas Furnaces," &c. By M. Faraday, Esq., D.O.L., LL.D., 

 F.R.S., Fullerian Professor of Chemistry, Royal Institution. 



The subject of the evening was gas glass-furnaces ; and having 

 arisen almost extemporaneously, it resolved itself chiefly into an 

 account of the manner in which Mr. Siemens has largely and practi- 

 cally applied gas, combined with the use of his heat-regenerator, to 

 the ignition of all kinds of great furnaces. Gas has been used to 

 supply heat, even upon a very large-scale, in some of the iron-blast- 

 furnaces ; and heat which has done work once has been carried back 

 in part to the place from whence it came to repeat its service ; but 

 Mr. Siemens has combined these two points, and successfully applied 

 them in a great variety of cases — as the potter's kiln, the enameller's 

 furnace, the zinc-distilling furnace, the tube-welding furnace, the 

 metal-melting furnace, the iron-puddling furnace, and the glass-fur- 

 nace either for covered or open pots — so as to obtain the highest 

 heat required over any extent of space, with great facility of manage- 

 ment, and with great economy (one-half) of fuel. The glass-furnace 

 described had an area of 28 feet long and 14 feet wide, and contained 

 eight open pots, each holding nearly two tons of material. 



The gaseous fuel is obtained by the mutual action of coal, air, and 

 water at a moderate red heat. A brick chamber, perhaps 6 feet by 

 12, and about 10 feet high, has one of its end walls converted into a 

 fire-grate ; i. e. about halfway down it is a solid plate, and for the 

 rest of the distance consists of strong horizontal plate-bars where air 

 enters, the whole being at an inclination such as that which the side 

 of a heap of coals would naturally take. Coals are poured, through 

 openings above, upon this combination of wall and grate, and being 

 fired at the under surface, they burn at the place where the air enters ; 

 but as the layer of coal is from 2 to 3 feet thick, various operations 

 go on in those parts of the fuel which cannot burn for want of air. 

 Thus the upper and cooler part of the coal produces a larger body of 

 hydrocarbons ; the cinders or coke which are not volatilized approach, 

 in descending, towards the grate ; that part which is nearest the 

 grate burns with the entering air into carbonic acid, and the heat 

 evolved ignites the mass above it ; the carbonic acid, passing slowly 

 through the ignited carbon, becomes converted into carbonic oxide, 

 and mingles in the upper part of the chamber (or gas-producer) with 

 the former hydrocarbons. The water, which is purposely introduced 



