304 THE UTILISATION OF WOODLAND PRODUCE. 



of 140 Ibs. per square inch and at a temperature of 120 F. ; 

 and 



4. Boucherie's method (1840), by injecting a 1-per-cent solution 

 of sulphate of copper (blue vitriol) under a pressure of 14 to 28 

 Ibs. per square inch by means of a guttapercha tube conveying 

 the solution from a tank 30 to 33 ft. overhead into a narrow 

 chamber formed by a cap fitting over one end of the log, so as 

 to force out the sap from the other free end as the solution 

 presses its way in a process which is easier in the case of green 

 than of seasoned wood. 



The corrosive sublimate method preserves well, but is dear and 

 poisonous, corroding iron and causing sores on workmen's 

 hands, and soon dissolving out in wet places. Chloride of zinc 

 is a weak antiseptic, and is easily soluble, but soon gets washed 

 out. Creosote is nearly as strong an antiseptic as corrosive sub- 

 limate, and is not poisonous ; but it is dear, pungent in odour, 

 and greatly increases the inflammability of wood treated ; it is 

 therefore only suitable for timber used in the open air, and not 

 for house-building timber and pitwood. Sulphate of copper is 

 a weak antiseptic and corrodes iron, but is the cheapest process. 

 Impregnating with creosote, originally introduced by Bethell in 

 1838, with pneumatic pressure, is now the chief British method. 

 The commercial creosote used is the crude heavy oil of tar 

 obtained by dry distillation of coal-tar (and not the true creosote 

 got by dry distillation of wood-tar), Its action is threefold, as 

 it (1) clogs up all pores in the wood, and so keeps out air ; 

 (2) coagulates the albumen ; and (3) acts as a poison to insects 

 and fungi. Barium salts are also good, cheap antiseptics. 



Creosoting with heavy coal-tar oil (boiling-point 365 F.)may 

 either take place by simple immersion in open iron tanks, or by 

 injection under pressure in closed iron cylinders. The simplest 

 and cheapest way to treat small quantities of well-seasoned 

 wood (such as fence-posts, &c.) is by immersion, and to pack it 

 (after being warmed, if convenient) into the open tank, and fill 



