MANUFACTURE OP WOOD-GAS. 133 



ILLUMINATING GAS FROM WOOD. 



Gas is now made of great excellence from wood, and in countries 

 where the price of coal suitable for gas-works has raised above the point 

 at which it could be used with profit, experiments have been going on 

 for years, in the hope of finding an economical substitute. Wood, 

 peat, the dregs of grapes, and other substances have been tried. The 

 first results with wood proved so unsatisfactory, that it was for a time 

 abandoned, as gas obtained at a low heat has but moderate illuminat- 

 ing power.^ 



In 1869, Pettenkofer, of Munich, in experimenting upon the carbon- 

 ization of wood, observed that the gas obtained at low temperatures- 

 was not rich in the hydrocarbons, but that when raised to a cherry -red 

 heat, the gases disengaged by the reaction of the elements were, when 

 purified, much superior in illuminating power to the best obtained from 

 coal. With this discovery Eiedinger has been able to establish the 

 manufacture of wood-gas as a profitable industry. 



The kind of wood used for gas appears to have but little influence 

 upon the yield, as is shown by the following table : 



CuMc meters of purified Gas obtained from 100 kilograms of Wood."^ 



Pine 33,840 



Fir 38,880 



Poplar 35,440 



Bass-wood 39,600 



Larch 33,000 



Willow 39,600 



Oak 34,020 



Beech 33,450 



The hygrometrical condition, however, has much influence, as well 

 upon the quality as the quantity of the gas-product; in fact, we notice 

 that if a part of the wood be already carbonized, the portion not decom- 

 posed will disengage the vapor of water, which, passing over the incan- 

 descent carbon, will form much oxide of carbon and of hydrogen, which 

 will proportionally reduce the illuminating power of the gas. From the 

 above it will be inferred that in making gas from wood, we should select 

 the kinds that commercially offer the greatest advantage, without being 

 particular as to the kind ; and, furthermore, that it should be dried as 

 much as possible before using, and be used as soon after drying as may 

 be, because it will rapidly regain by absorption from the air much of the 

 moisture it has lost.^ 



• The first person who attempted to submit wood to distillation for the purpose of 

 obtaining gas and other products, was Philip Lebon, near the close of the last cen- 

 tury; and in the year VIII (1799) he took out a French patent for new methods of 

 using combustibles with greater economy, as well for heat as for light, and for collect- 

 ing the difterent products. Three years after, he obtained the use of a part of the 

 Eouvray forest, near Havre, for the manufacture of tar, engaging to deliver five 

 quintals a day, and with apparatus of large dimensions he was able to supply a nota- 

 ble quantity of tar for the marine. He died in Paris in December, 1804, and the busi- 

 ness was continued under his widow's direction till 1811. 



2 By dividing these quantities by 16 we shall have very nearly the cubic feet of gas 

 from one pound of wood. 



3 In practice, they use for this purpose the heat lost in the distilling-ovens, by build- 

 ing behind them a room in masonry, which becomes a true stove, the floor being made 

 of cast-iron plates, under which the products of combustion pass from the ovens to the 

 chimney. The wood is piled in this room and left about twenty-four hours. It is then 

 taken out, to be placed from time to time, as occasion requires, in the retorts of the 

 gas-works. 



The retorts for making wood-gas should be so arranged that the volatile products 

 should be subjected for a certain time to a high temperature. The first ones employed 

 were divided by partitions, and the disengaged products passed into the exterior com- 

 partments, the wood being placed in the middle. But this form of apparatus was 

 found so inconvenient in practice, that they were obliged to abandon its use. Eiedinger 

 attempted to use the common gas- retorts", making them considerably larger than the 

 charge of wood, and obtained very good results, which has led to the general use of 

 retorts of this kind. The wood gives off very rapidly a large amount of gaseous prod- 



