252 CHEMICAL FERTILIZERS 



useful germicides, but the higher phenols are much more 

 poisonous than the simpler phenols. When coal is distilled, 

 a tar is produced, which on redistillation yields a fraction 

 called creosote, which, on extraction with caustic soda, 

 yields a mixture of tar acids in combination with the soda 

 employed. On treatment with acids the tar acids are set 

 free. Pure phenol is oxidized by bacteria in the soil to 

 trihydroxy-glutaric acid ; the higher phenols are very 

 resistant to bacterial action. Winter sheep dips are gener- 

 ally made from 2 parts of creosote and i part of a 

 20 % solution of caustic soda. The creosote must be rich 

 in tar acids, for which purpose a Midland or South Country 

 gas tar creosote is the most suitable. Blast-furnace creosotes 

 contain much hydrocarbon, which checks emulsification, 

 whilst North Country gas tar is rich in naphthalene, which 

 has a similarly retarding influence. The addition of wood 

 tar or soap increases the emulsification of the mixture. 

 Crude tar containing much free carbon is quite unsuited 

 for the manufacture of sheep dips, as the carbon is not 

 easily removed from the wool. 



Creosote. The middle fractions obtained on the dis- 

 tillation of coal tar are used for preserving timber. The 

 preservative effect of creosote depends partly upon the 

 proportion of tar acids, but also upon the more complex 

 hydrocarbons. The result is complicated by the double 

 action of waterproofing and poisoning that takes place at 

 the same time, both of which duties are performed by most 

 of the ingredients present. Preservation of timber may be 

 carried out by merely painting on the surface, when the 

 benefit is uncertain. By immersing timber in hot creosote 

 much better penetration is obtained, but the amount of 

 creosote used is large. By the pressure process creosote 

 is forced into the vessels of the wood and, after soaking, 

 the excess of creosote may be removed by reversing the 

 pumps. An alternative method is to employ emulsification. 

 By mixing creosote, water and caustic soda, so as to produce 

 not less than a 20 % creosote and J % soda emulsion, deep 

 penetration of the fibres of the wood can be obtained by 



