PRESERVATION OF TIMBER. 351 



the light or the heavy dead oils are the most suitable for 

 efficiently preserving timber; the earlier introducers of the 

 process certainly advocated the use of the latter, containing 

 napthalene, etc. ; * while, later, the thinner oils, containing more 

 of the tar acids, such as carbolic acid, were preferred. 2 This 

 view is again controverted by others, who now hold that it is 

 only the heavy oils which can be relied upon to excite a con- 

 tinuous preservative action, the creosote itself being liable to 

 become dissipated in course of time. 8 Mr. Boulton advocates 

 an admixture of both, 4 provided neither were so manipulated 

 as to contain a larger proportion of volatile substances at the 

 expense of the more durable, and therefore, for this purpose, more 

 valuable antiseptics. 5 



In view of the more penetrating power of the thinner oils, 

 Mr. F. M. Roberts suggests that the best system of creosoting 

 timber would be to first inject the light, or country, oil, then, 

 running this off, using the heavy, or London, oil, which being 

 forced in by increased pressure would drive the thinner oil 

 further in, while the thicker and heavier oil would hermetically 

 seal the outer pores of the timber. 6 



Without pressure, light oils penetrate timber more easily 

 than heavy oils. Of adulterative substances, bone oil pene- 

 trates more readily than creosote; solutions of metallic salts 

 more readily still ; and water more readily than all. Those 

 substances which penetrate most readily are generally the least 

 permanent. 7 



The reasons why tar, in its entirety, is not adopted in the 

 preservation of timber, are that the crude napthas or oils lighter 

 than water are useless as antiseptics, and would immediately 

 evaporate, whilst the pitch, from its too great solidity, would 

 form an impediment to the injection. 8 



Carbolic Acid has been looked upon as one of the most 

 important ingredients of creosote as a preservative of timber, 

 and as an antiseptic it is one of the most powerful amongst 

 the tar acids ; but it appears to be now recognized that, owing 

 to the fact, as determined by numerous and reliable authorities, 

 of its being volatile at ordinary temperatures, it is soluble 

 in water, that its combinations are not stable ; that, although 



1 M.P.I.C.E., vol. Ixxviii., p. 108. 2 Ibid., 110. 



s Engineering, vol. 1. p. 607. M.P.I.C.K, vol. Ixxviii. p. 119. 



4 Hid., p. 197. 6 Ibid., 189. ' 76^., 194. Hid., p. 107. 



