WOOD-GAS: DISTILLED PRODUCTS. 135 



When wood is submitted to distillation in close vessels, the volatile 

 products, beside gases, vary according to the nature of the wood, the 

 temperature, and the time employed in the process. There come over 

 the vapor of water, mingled with acetic acid, methylic alcohol, acetate 

 of methyl, acetone, creosote, phenols, and tar-like substances of complex 

 composition, and of relatively small amount.^ 



•with a given orifice, and under equal pressure, tbo amonnt of gas passing out will be 

 in proportion to the square root of the density. Moreover, to burn the oxide of car- 

 bon, which forms so large a proportion in wood-gas, we need much less air than in 

 burning a gas rich in protocarbonated hydrogen. The air will penetrate more rapidly a 

 jet of wood-gas than a similar one of coal-gas, and if we do not increase the thickness 

 of the jet of gas, the relative excess of air will reduce the illuminating power to a 

 point that will, so to speak, annul it. We see, therefore, that burners that operate well 

 ■with coal-gas would not serve the pui-pose with wood-gas, and vice versa, under a 



Eressure of 2 to 3 millimeters of water (about V? to i of an inch), the bat-wing tips, 

 aving a width of about 0'""". 9 (0.0394 inch.) gives the best results with wood-gas. 

 The secondary products in the making of wood-gas are tar-water and charcoal. The 

 former of these, condensed in the receiving-cask and in the refrigerators beyond, are 

 left to stand in wooden tanks to allow the tar to separate from the acid waters, and the 

 latter are then saturated with quicklime, so as to form the pyrolignite of lime by 

 processes above indicated, which reduces quite considerably the cost of making gas. 

 From one hundred parts of wood they get fifty to seventy-five of the crude acetate of 

 lime, dry. The tar when separated will serve to mix with coal-dust, or may be used 

 directly for painting. They represent about 2 per cent, in weight of the dry wood 

 «sed. The charcoal is very light when carbonized quickly from tender woods, and 

 burns easily and rapidly. It serves very well for domestic use, and is bure to find a ready 

 Bale in cities. 



The advantages of wood-gas are as follows: It is completely free from sulphurous 

 fumes, which do so much injury to paints having lead as their base, as often happens 

 •with coal-gas when imperfectly purified, and in burning it gives out no sulphurous 

 acid. A given weight of wood will furnish more gas than a like weight of coal, and 

 more rapidly. It follows that for a given production, a considerable less amount of 

 apparatus is needed, and less space than fqr coal-gas. The making of wood-gas is 

 more profitable than from coal wherever pine or fir wood (not floated) costs less than 

 coal-gas; but we must always take into account the lime needed in purifying, which 

 is sometimes difiicult to obtain at a low price in certain localities. 



But we may use wood of inferior quality and of all sizes, and in very many locali- 

 ties it will be found that the cost is altogether in favor of wood-gas. — (Carbonisation 

 des Bois en vases clos, et utilisation des jprodwits derives. By Camille Vincent. Paris, 1873, 

 p. 14'i.) 



1 The liquid products passing over and condensed in a wooden cask, separate into 

 three distinct strata : the lower of tar and the heavy creosote oils, saturated with acetic 

 acid ; the middle, of water, pyroligneous acid, wood spirits, acetone, and the tarry 

 compounds having affinity with acetic acid, and wood spirits, methyl-acetic ether, and 

 oxyphenic acid ; and the upper layer, of the light and tarry oils, holding acetic acid in 

 solution. These are drawn oif by faucets placed at different levels, and by separate 

 treatment, which we cannot here detail, finally yield the following products : 



Acetic acid, of various grades, for use in the arts, and for table use, and the varied 



acetates used in coloring and otherwise, as the acetates of soda, potash, ammonia, bary- 



• tes, lime, manganese, alumina, magnesia, iron, chromium, zinc, nickel, cobalt, lead, 



mercury, silver, bismuth, antimony, uranium, aud copper, with various neutral, sea- 



quibasic, bibasic, and tribasic acetates, and other combinations in great variety. 



Pyrolignites of lime, iron, and lead : methylic alcohol, and others, with combinations 

 of oxygen, chlorine, bromine, iodine, fluorine, cyanogen, sulphur, nitrogen, boron, &c., 

 and a large and constantly increasing number of products, many of them of known use, 

 and others of only scientific in' erest, result from the chemical processes applied to 

 these liquid products of distillation of wood. Their principal use is iu furnishing an- 

 tiseptic materials for increasing the durability of timber and other organic materials, 

 aud in supplying mordants and dyes for coloring. 



There are two classes of distilling apparatus. In one, the external air is admitted, 

 as in the meiler and kiln, where carbonization is eliected at the expense of a part of the 

 •wood carbonized ; and in the other, the retorts are wholly closed aud heat is applied 

 entirely from without. The latter are subdivided iuto fixed and movable apparatus, 

 the latter implying cranes aud other machinery for lifting and placing the receivers and 

 their contents. 



The best results, where all products are saved and all precautions are adopted, give 

 charcoal 26 parts, pyroligneous acid and water 30 parts, tar 7 parts, carbonic acid aud 

 oxide, hydro-carbon and vapor of water not condensed, 37 parts. The weight of •wood 

 added as fuel to effect this distiUation, is about 12^ parts. 



