GAS, COAL 549 



invented for the production of gas, and which, although in its present form too com- 

 plicated for successful practical use, yet embodies, when we consider the early date of 

 its invention, in a remarkable manner, the true scientific principles of gas-making. 

 This retort, of which a description will be found at p. 578, obviated to a great extent 

 the inequality and uncertainty of temperature in the ordinary gas-retorts, and the 

 result was an increase of from 30 to 40 per cent, in the quantity of gas produced, the 

 quality being also improved, whilst scarcely any tar was formed. 



But besides the great influence exercised by the temperature to which coal is 

 exposed in the process of gas-making, the length of time, during which the volatile 

 product* of decomposition are exposed to that temperature, is a most important cir- 

 cumstance as regards the successful manufacture of gas. If we take into consideration 

 the behaviour of the luminiferous constituents of gas when exposed to a bright red 

 heat, and which has been described above, it will be evident that a second most im- 

 portant condition in the manufacture of gas is the rapid removal of these luminiferous 

 constituents from the destructive influence of the red-hot retort as soon as they are 

 generated : every second during which these gases are allowed to remain in their 

 birthplace diminishes their value as illuminating agents. The only method hitherto 

 employed for the rapid removal of the gases from the retorts is White's process, the 

 mechanical details of which are fully described below. This process consists 

 essentially in transmitting a current of water-gas through the retorts in which coal 

 or cannel gas is being generated. The water-gas is produced by transmitting steam 

 through retorts filled with coke or charcoal, and consists of a mixture of hydrogen, 

 carbonic oxide, and carbonic acid gases. These gases, which are not in themselves 

 luminiferous on combustion, necessarily become mixed with the coal or cannel gas, 

 and thus diminish the illuminating power of the latter whilst they increase its volume. 

 Nevertheless, if the admission of water-gas be properly managed, the luminiferous 

 constituents saved from destruction by their rapid removal from the retorts, compen- 

 sate for the dilution of the gas, so as to render the diluted gas equal in illuminating 

 power to the gas produced from the same coal or cannel in the ordinary process of 

 manufacture. When cannels yielding very highly luminiferous gas are employed, it 

 is desirable to dilute them to a much greater extent, and this can be easily effected 

 by admitting into the coal-retort a larger proportion of water-gas. In some cases the 

 total amount of light yielded by the gas from a given weight of coal when treated 

 according to White's process is more than double that obtained by the ordinary pro- 

 cess, and in all cases the gain in total amount of light is very large, thus showing the 

 importance of removing the gases from the red-hot retorts as rapidly as possible. 

 This remark applies especially to gases very rich in luminiferous hydrocarbons, 

 because such gases suffer relatively much more deterioration than those containing a 

 larger proportion of diluents. In addition to these advantages, such a dilution of rich 

 cannel-gases with any of the non-luminous constituents, hydrogen, carbonic oxide, or 

 light carburetted hydrogen, increases the illuminating power of the gas in another 

 way : this is effected by their forming a medium for the solution of the vapours of such 

 hydrocarbons as exist in the liquid or even solid state at the ordinary temperature of 

 the atmosphere, and they thus enable us to convert an additional quantity of illumi- 

 nating materials into the gaseous form, which they retain permanently, unless the 

 temperature fall below the point of saturation. The gain in illuminating power 

 which is thus obtained will be perhaps better seen from the following example : 

 Suppose 100 cubic inches of olefiant gas were allowed to saturate itself with the 

 vapour of a volatile hydrocarbon, containing three times as much carbon in a given 

 volume of its vapour as that contained in an equal volume of olefiant gas, and that it 

 took up or dissolved 3 cubic inches of this vapour ; then, if we express the valuo of 

 1 cubic inch of olefiant gas by unity, the illuminating power of the 103 cubic inches 

 of the mixture of olefiant gas and hydrocarbon-vapour will be 109. Now if we mix 

 these 103 cubic inches with 100 cubic inches of hydrogen, the mixture will be able to 

 take up an additional 3 cubic inches of hydrocarbon-vapour, and the illuminating 

 power of the 206 cubic inches will then become 118 ; thus the hydrogen produces a 

 gain in illuminating power equal to 9 cubic inches of olefiant gas, or nearly 4'5 per 

 cent, upon the volume of mixed gases. When we consider that coal-naphtha contains 

 hydrocarbons of great volatility, and that these are the surplus remaining after tl^p 

 saturation of the gas from which they are condensed, the importance of this function 

 of the non-illuminating class of combustible gases will be sufficiently evident. It may 

 here be remarked that incombustible gases could not be employed for this purpose, 

 since their cooling influence upon the flame during the subsequent burning of the 

 gas would diminish the light to a greater extent than the hydrocarbon- vapour could 

 increase it. 



It is evident that all the three non-illuminating gases, forming the class of diluents, 

 would perform both the pfficeg Ijeje assignee} to them perfectly well, and therefore we 



