526 AUXILIARY FOREST INDUSTRIES. 



obtained between 150 and 280 are the most valuable, and 

 are chiefly sebacic acids, such as formic, acetic, propionic, 

 valerianic, caproic acids, then methyl- alcohol, carbonic acid 

 and carbon monoxide. Between 280 and 360 chiefly carbo- 

 hydrates are formed ; they take up much space, as 1 cub. 

 meter of wood yields 80 to 90 volumes of gas. The products 

 of heating over 360 are dense carbohydrates (tars), such as 

 benzol, toluol (methyl-benzene), carbolic acid, paraffin, and 

 the gases acetyl, ethyls, marsh-gas and hydrogen. By heating 

 over 430, there is a small volume of the above-named 

 substances, whilst charcoal remains as a solid residual 

 product. 



In every case, when quite pure, hydrated acetic acid is a 

 colourless liquid, combustible, very caustic and with a strongly 

 acid odour ; at 4 C. acetic acid becomes solid, but lignifies 

 at 16 ; after absorbing water it loses its power of crystallisa- 

 tion ; hydrated acetic acid is soluble in water, alcohol and 

 ether. Wood yields 2 to 6% of its weight in pure acetic acid, 

 which is used extensively for making vinegar. In wood- 

 vinegar there is always some acetone, a combustible liquid 

 in which oils, resin and gun-cotton are very soluble ; it is 

 now used in the manufacture of smokeless powder. 



Pure methyl-alcohol or pyroligneous spirit is a colourless 

 liquid, in which resin and ethereal oils are very soluble, so 

 that it is highly important in preparing lacquers and varnishes; 

 after further distillation pure methyl-alcohol is used for making 

 tar dyes. 



The gas distilled from wood, 80 cubic meters from a stacked 

 cubic meter, owing to admixtures of C02 and CO, requires 

 purifying by means of lime. [In France charcoal is placed 

 at the base of the retort in which the wood is distilled, and 

 the gas passes through the charcoal into a reservoir. This 

 is said to purify it sufficiently. Tr.] According to Pettenkofer 

 the volumes of illuminating wood-gas produced by distilling 

 100 kilos (220 Ibs.) of wood are : 



Cubic meters. Cubic feet. 



Willow . . . .38 1,330 



Silver-fir . . 36 1,260 



