GAS, COAL 



551 



raent of the retorts, by which the distillation of coal is greatly facilitated. It has now 

 been experimentally in use, upon a working scale, in the manufactory of the Chartered 

 Gas Company in the Horseferry-road, and is established on a larger scale at their 

 principal works at Beckton. Instead of the usual horizontal retorts, which are 

 charged and emptied with great difficulty by severe labour, Messrs. Porter and Lane 

 use vertical retorts, within which a screw, with an .oblique blade, slowly revolves on 

 n vertical axis. The coal is placed in a chamber or hopper above, and trickles down 

 into the retort as room is made for it by the subsidence qf tha,t which is below. The 

 tus is, therefore, self-feeding, und only requir.es that the hopper should be sup- 



plied at proper intervals by easy labour, such as can be done by anyone who can 

 handle a spade and a barrow. The revolution of the screw keeps a spiral line of coal 

 in constant contact with the inner side of the retor.t ; and the intervals, between the 

 turns of the blade allow room for the disengagement of the gas. By the time the coal 

 reaches the bottom of the screw it is exhausted, and it falls as coke into a vertical 

 chamber below, which is continuous with the retort, but beneath the furnace, and in 

 which it is instantly quenched. The coke-chamber can be emptied by one man, as 

 often as necessary, in one minute ; and the whole process requires scarcely any inter- 

 ference from those in charge of it. By establishing a proper relation between the 

 length of the screw, the speed of its rotation, and the heat of the furnace, the distil- 

 lation of the coal can be carried exactly to the most desirable point, so as to obtain 

 from it all the gas it can yield, and to stop short of the evolution of a variety of 

 noxious products. In the horizontal retorts the outer crust of the mass of enclosed 

 coal becomes over-burnt long before the inner portion is exhausted, and in this way 

 many sulphur compounds are produced, even although the charge, as a whole, is with- 

 drawn flaming and manifestly unexhausted. In Porter and Lane's process, on the 

 contrary, the charge falls out bit by bit in a glowing condition, and yields a coko 

 which is said to be much better adapted for household purposes than that ordinarily 

 made. It is said to be lighter and more spongy in texture, and to kindle readily 

 when placed on a common fire ; but it burns out with great rapidity. 



The results hitherto obtained by this method at the works of the Chartered Gas 

 Company seem to show a constantly -increased production of gas to the extent of 2,000 

 cubic feet for each ton of coal, and also an increased production of coke. Moreover, 

 the division and distribution of coal by the screw exposes it so completely to the action 

 of heat that the retorts may Lo kept at a lower temperature than in the ordinary 

 method, and thus the life of eack retort will be proportionately prolonged. The 

 saving of labour, of course, speaks for itself; and the quality of the gas, especially 

 with reference to the presence of sulphur-compounds, is very superior to that made 

 in the usual way. The retorts remain free from carbonaceous deposit, and their 

 vertical arrangement has admitted of improvement in the furnace, by which a con- 

 siderable saving in repairs, fuel, and labour is effected. 



The following remarks on the manufacture of gas for illuminating purposes are 

 mainly derived from a paper read by Mr. Thomas Wills before the Society of Arts. 

 After a few remarks on the constitution of wood, lignite, and coal, and the products 

 of their gradual resolution into simpler compounds, their more rapid decomposition by 

 heat was illustrated by the following table, showing the proportion of hydrogen and 

 carbon in coal-gas as distilled at different temperatures, the hydrogen being maintained 

 constant : 



The number of well-known intermediate products obtained during the destructive 

 distillation of coal is very large, and coal-gas itself not only contains certain perma- 

 nent gases, but also a large quantity of the vapours of volatile hydrocarbons, which 

 contribute in no small degree to its luminosity. Still, the greater bulk of the gas is 

 composed of hydrogen, the flame of which is without any light-giving properties 

 whatever, and marsh gas, a gas possessing the least light-giving power of any 

 hydrocarbon, as it contains tjje smallest proportion of carbon to tb,e largest of 

 hydrogen, 



