350 NOTES ON DOCKS AND DOCK CONSTRUCTION. 



carbolic acid, or phenol, which was thought by some to l>o 

 identical with the creosote of wood, the process came to be 

 called after a time the creosoting process. 1 



The antiseptic substances used in the process are all obtained 

 by the distillation of coal-tar, which is subjected to heat placed 

 beneath the still. The operation is sometimes aided by the 

 injection of steam, and sometimes by the application of the 

 exhausting air-pump. The products of distillation come over 

 very nearly in the order of their respective volatilities, tli 

 of lightest specific gravity being followed in succession by 

 heavier ones as the heat increases. The result is to break up 

 the tar into three groups of products, viz. oils lighter than 

 water ; oils heavier than water ; and pitch. 2 



The heavy oils of tar, or dead oils heavier than water, 

 constitute the " creosote " of the timber-yards. They contain 

 numerous substances, some of them liquid, some semi-fluid, 

 varying considerably in their properties, but most of them 

 now recognized as antiseptics. 8 



"London Oils. The dead oils made in London and in all 

 places where the tar is produced by the carbonization of the 

 coal of the Newcastle district, are, as compared with other dead 

 oils, richest in semi-solid substances, such as napthalene, anthra- 

 cene, pyrene, etc., and they require a higher temperature to 

 volatilize. These are generally called London oils." 



"Country Oils. The dead oils of the Midland districts are 

 lighter, thinner, and more volatile, and contain usually a larger 

 proportion of the ordinary tar acids. These are usually called 

 country oils." 



"Scotch Oils are, many of them, still lighter, thinner, and 

 more volatile, sometimes lighter than water." 4 



The process of creosoting consists in thoroughly impregnating 

 the timber with the heavy tar-oils, the object being to coagulate 

 the albuminous substances in the sap remaining in the wood, 

 but chiefly to thoroughly fill the pores with an imperishaMr. 

 antiseptic substance which renders the timber impervious to 

 air and moisture, and acts, in the opinion of Dr. Letheby, as a 

 positive poison to the lower forms of animal life. Timber 

 treated by this process retains all its original elasticity. 



Some difference of opinion appears to exist as to 



, vol. Ixxviii. p. 103. - Ibid., 10G. J ll>;<L t 107. 



4 llnil, p. 108. 



