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THE SCIENTIFIC PAPERS OF 



until at the end of the fourth hour it is less than half what it was 

 at the earlier portion of the process. 



Now, if the gas produced in the retort could be directed by a 

 simple reversing valve into one main or the other the illuminating 

 power would rise from 18| to 18 caudle-power, and produce thus 

 all the advantages which the public now desire, a gas of increased 

 illuminating power ; whereas the heating gas constituting the 

 other half, or even two-thirds, of the total produce, would be all 

 the better qualified for heating purposes than the gas which is now 

 sent into our mains. It is well known that marsh gas produces 

 a higher calorific effect weight for weight than olefiant gas. 

 Therefore, if the marsh gas, and the hydrogen, which has still 

 higher calorific power, could be supplied separately, we should 

 get a better illuminating gas, and a better heating gas. It may 

 be objected that this would involve the laying down of a separate 

 set of mains ; but in answer to that, I contend that in many towns 

 we have already two sets of mains, because at one time or another 

 we have had opposing Gas Companies, each with their set of 

 mains ; but even if they do not exist, the question of the supply of 

 heating gas is such a large one, that the laying down of additional 

 mains should not stand in the way. If gas heating is to come 

 into general use, we shall soon require perhaps three or four times 

 the amount of gas which can possibly be supplied through the 

 existing mains. If at the same time such a great advantage can 

 be realised as the production of a gas of a higher illuminating 

 power, and with it a heating gas at lower cost, we should have an 

 advantage every way. But with regard to the question of cost, of 

 course, the public would be willing to pay a somewhat increased 

 price for a gas of 40 or 50 per cent, increased illuminating power, 

 whilst the heating gas, on the other hand, would not require the 

 same amount of care and expense in purifying as is necessary for 

 illuminating gas. 



Then for this Society the question has another important aspect. 

 If by the supply of heating gas the total consumption can be vastly 

 increased the bye-products would be increased in the same pro- 

 portion, and these bye-products have now attained an im- 

 portance only second to that of the value of the gas itself. 

 Therefore, if by the carrying out of such a plan the total pro- 

 duction of gas can be very greatly increased, an impulse would 



