552 GAS, COAL 



Average Composition of Coal- Gas supplied by the following Companies: 



There can be no question that a great advance in the manufacture of coal-gas would 

 be made if, by any means, applied either with primary distillation of the coal or to the 

 gas after its production, whereby the amount of acetylene (C 2 H 2 ) or of olefiant gas 

 (C 2 H 4 ) could be increased; for olefiant gas contains, in a given bulk, just twice as 

 much carbon as marsh gas, and acetylene a still larger quantity. The value of this 

 increase is not to be measured only by the increased quantity of carbon contained in a 

 given bulk of gas, for a small portion of either of the above compounds, diffused 

 through a non-illuminating gas, is much more than equivalent to a similar quantity 

 of carbon combined in some less condensed compound. An illustration of this occurs 

 in the case of marsh gas. If marsh gas, possessing, it will be remembered, only a 

 small amount of luminosity, be decomposed, either by its passage through a heated 

 tube, or by the electric spark, the carbon it contains will be deposited, while the 

 amount of hydrogen set free will occupy double the volume of the original gas. Yet 

 the flame of this nearly pure hydrogen will be found to possess a greater luminosity 

 than the flame of the original marsh gas, although it has lost nearly the whole of 

 its light-giving material, accounted for by the presence of a very small quantity of 

 acetylene, produced during the decomposition. 



In 1871 a patent was taken out for ' Improvements in the manufacture and puri- 

 fication of gas, and in certain parts of the apparatus employed therein.' This process 

 is carried out by distilling the coal at a much lower temperature than usual in the 

 original scheme from 600 to 1,000 Fah. is mentioned, but in practice from 1,300 to 

 1 ,400 Fahr. will probably be employed ; at this temperature, from a ton of gas-coal 

 about 8,500 cubic feet of gas are obtained, together with a greater than ordinary yield 

 of tar and oil : this tar is condensed, by special means employed for securing a greater 

 rapidity in the process, and collected as free from water as possible, with a view to its 

 being re-distilled in a separate and peculiar retort. 



The following are some of the more important points brought out by examination 

 of this process by Messrs. Keates and Odling. The highest yield of gas obtained 

 directly from the coal was 9,775 cubic feet, the temperature of distillation being 

 between 1,300 and 1,400 Fahr. The quantity of oil and tar obtained from one ton 

 of coal varied considerably with the nature of the coal used ; thus, Silkstone coal-gas 

 16'4 gallons of tar and oil per ton, Clay Cross main 11 '9 gallons, and Pelawmain 13'9 

 gallons, or a mean of 14 gallons. The highest yield of gas which was obtained by the 

 continued distillation and redistillation of the oily tar was 29 cubic feet per gallon. 

 The mean lighting power of the gas produced from coal was 23-0 candles, and of that 

 obtained from the tar 25'0 candles. The quantity of coke used to maintain the heat 

 in the various parts of the apparatus was about 33 per cent, of that produced, and 

 in the event of the distillation being repeated until complete separation into pitch 

 and vaporisable matters tikes place, this amount would be much exceeded. It is a 

 generally-accepted fact that the quicker coal bo carbonised in gas-making, provided it 

 bo done effectually, the more successful will bo the operation. A plan for effecting 

 this has recently been brought forward, the principle of which is as follows : The 

 retort in this case is set in a vortical position, and through its centre revolves a broad 

 and somewhat deep screw, placed together in sections, the thread of which is placed at 

 an angle of 45, and which comes nearly into contact with the sides of the retort. 

 Through a nipple at the top, coal is supplied, in pieces of small but regular size ; the 

 inclination of the thre.'id of the screw impels the pieces against the heated sides, where 

 comparatively rapid carbonis.it ion tikes place, and the rate of revolution of the screw 

 is so regulated, that by the time the fuel has arrived at the bottom of the retort the 

 process is complete, and coke of a somewhat inferior quality is discharged into a 

 suitable receptacle. The yield of gas is greater by this means, and of higher illumU 



