GAS, COAL 



553 



nating power, the amount of tar being correspondingly less ; the difficulties in this case 

 appear to be chiefly mechanical. That the process is successful, will be seen from the 

 following results : 



The fact of the existence of a large number of hydrocarbons of great volatility, the 

 vapours of which, when ignited, burn with exceedingly liiminouB flame, has been a 

 very great incentive with inventors to produce some scheme whereby these vapours 

 might be used to confer luminosity upon a combustible non-luminous gas, or 

 further inflammability, coupled with luminosity, upon a non-combustible and negative 

 gas. 



Another process which has claimed some attention is that of Dr. Eveleigh, which 

 has been used by the Patent Gas Company, and investigated, and reported on, by 

 Dr. Odling and Mr. Keates. 



The process consists in the distillation of coal in iron retorts of double the ordinary 

 capacity, at a lower temperature than that usually employed. A smaller yield of gas 

 is thus procured of comparatively high lighting power, together with a certain quantity 

 of oily tar, which is subsequently submitted to destructive distillation in a peculiarly- 

 constructed apparatus, in which the oil suffers a partial conversion into permanent gas. 

 These two processes are, in practice, carried on simultaneously, the resulting gases 

 mixing during their passage to the holder. The combined result of the distillation 

 of the coal and oil by this method gives a larger yield of gas per ton of coal, it is of 

 considerably higher lighting power, and is comparatively free from sulphur-com- 

 pounds. 



The apparatus used for the distillation of the oil consists of three vessels placed at 

 increasing distances from the source of heat. The oil flows into that having the 

 lowest temperature (about 900 F.), where the fixed portion of the oil remains as 

 pitch, while the more volatile vapour, after becoming further heated by passing through 

 the second chamber, enters the last or hottest vessel. This is an iron pan filled with 

 charcoal, and heated to about 1,300 F. The highly-heated vapour of the oil, during 

 its passage through the incandescent charcoal, is partially converted into permanent 

 gas. This gas, after leaving the oil-still, enters a tank containing a little water, 

 through which it passes, in order to condense any undecomposed oil : it is then con- 

 ducted along a pipe, where it meets with the gas from the coal, the mixture going 

 through the purifiers to the holder in the usual way. 



The highest yield of gas obtained by this method from ordinary Norfolk Silkstone 

 coal, during the experiments of Mr. Keates and Dr. Odling, was 10,500 cubic feet of 

 25-candle gas to the ton, the sulphur being as low as 6 grains per 100 cubic feet. 

 This is certainly a striking result, as compared with the ordinary yield of the same 

 coal, which is about 9,300 feet of 14-candle gas, frequently containing over 30 grains 

 of sulphur per 100 feet. 



Although it has been proved possible to obtain the above favourable result by Dr. 

 Eveleigh's process, it is to be feared that the extra amount of plant, labour, and fuel 

 required, necessitates such increased expenditure as to more than compensate for the 

 increased yield. 



On the purification of illuminating gas. If we except the insignificant quantities of 

 nitrogen and oxygen, which become mixed with illuminating gas through imperfections 

 in the joints of the apparatus employed, and by the transferring power of the water 

 of the gasholder, all impurities arise from the presence of the three elements sulphur, 

 oxygen, and nitrogen in the generating material used. 



The sulphur, uniting with portions of the hydrogen and carbon of the coal, gene- 

 rates, with the first-named element, sulphuretted hydrogen, and with the second, 

 bisulphide of carbon. It is also probable that volatile organic compounds of sulphur 

 are produced by the union of this element with carbon and hydrogen simultaneously, 

 although we have as yet no positive evidence of their presence in illuminating gas. 

 The oxygen, uniting with another portion of carbon, forms carbonic acid, whilst the 

 nitrogen unites with hydrogen to form ammonia, which, by combination with sul- 

 phuretted hydrogen, produces hydrosulphate of sulphide of ammonium, and, with 

 carbonic acid and water, carbonate of ammonia. With the exception of bisulphide of 

 carbon and the organic sulphur-compounds just mentioned, tl}6 removal of all these 



