130 PLANT PRODUCTS 



be 200® and 250° Cent., so that considerable loss of heat 

 occurs unless some means of utilization is devised. The 

 wood is placed in trucks and run into the retorts. If the 

 wood is fairly dry, 25 per cent, of charcoal will be left behind. 

 The charcoal is preferably rapidly transported in trucks to 

 a cooling chamber, which is often externally cooled by sprays 

 of water. When cold, the charcoal is placed in store. The 

 products of distillation are passed through a fractionating 

 arrangement, which causes the condensation of the heavier 

 tars, and then through an ordinary form of condenser, 

 where other substances condense. The gas passing away 

 contains considerable quantities of carbon monoxide, which 

 is burnt in the fire and assists in maintaining the temperature. 

 The tar which is separated in the tar separator is boiled to 

 drive oS the water which it still contains. The portion of 

 the distillate from which the tar has been removed, commonly 

 called pyro-ligneous acid, is then distilled, to remove the 

 acetone and methyl alcohol, which are subsequently 

 fractionated into pure products, with a still of somewhat 

 similar type to that used in all industrial concerns for 

 fractionation of volatile substances. The remaining acid is 

 then treated with lime, at the rate of about four pounds per 

 ten gallons liquor, when a heavy black sludge is thrown out, 

 consisting of any excess lime and compounds of the lime with 

 higher acids of the acetic series and polymerized forms of 

 aldehydes. After settling for some days, the clear liquid is 

 removed, boiled down, and, when nearly dry, run over heated 

 rollers to obtain the acetate of lime in a fine, dry state. Many 

 attempts have been made to produce a continuous apparatus, 

 but such are only suited to small wood. Small vertical retorts 

 also deal very efficiently with small wood. A very excellent 

 article on this subject is found in Thorpe's "Dictionary of 

 Applied Chemistry," under the title of " Wood." Where 

 the wood is scattered over large areas, it is necessary to 

 bring the still to the wood, rather than the reverse. For 

 this purpose a portable plant has been designed by the author 

 (see Bibliography). A portable machine of the type 

 described will consume nearly all the waste wood of about 



