176 TRANSACTIONS OF ROYAL SCOTTISH ARBORICULTURAL SOCIETY. 



escape, and the timber is left to drip until the following morning. 

 The trolleys with their load of timber are then withdrawn and 

 the process is completed. 



The cost of erecting a creosoting plant of the size named 

 above would amount to ;^3oo to ;{[s$o. 



2. The second or boiling method ^ has long been adopted 

 with considerable success, especially in the West of Scotland. 

 In this case, the plant may be either very simple or comparatively 

 elaborate. It may be said generally to consist of a boiler, 

 either oval shaped or with a flat bottom, which is enclosed in 

 brickwork and has a straight or winding flue. The flue is 

 furnished with a fairly long chimney, which has a damper to 

 regulate the draught. It is also advisable to have a storage 

 tank for the creosote, which may consist of a disused boiler, to 

 which is attached a pump. The pump is used to introduce the 

 creosote into the boiler, and a tap attached to a pipe connecting 

 the boiler with the storage tank is used to withdraw the surplus 

 at the close of the operation. 



The general principle is the same as in the previous method, 

 but there are variations in detail. It is desirable that the timber 

 should be as dry as possible, but if it is damp, the excess of 

 moisture may be removed during the operation of creosoting. 

 This naturally results from the fact that the fluid contents of the 

 timber consist mainly of water, which, under the pressure 

 conditions existing in the boiler, boils at a temperature lower 

 than that reached in the impregnating process, and it is thus 

 driven off' in advance. 



The temperature in the boiler should not, however, be allowed 

 to rise too high, as this is apt to partially char the wood, and 

 thus reduce its strength. The respective boiling points of water 

 and creosote are 212° F. and 365° F., and the desirable 

 temperature is one only slightly above the former. There is 

 grave risk of fire if it rises too near the boiling point of creosote. 



It is not easy to give the exact number of hours during which 

 the timber should remain in the hot creosote, but 36 to 48 hours is 

 usually considered to be the most suitable period. It is further 

 advantageous to leave the timber in the boiler for a few hours 

 after the fire has been put out. The reason is as follows : — 

 Cooling causes a condensation of the steam or a contraction of 



^ C/. paper by Mr George Leven in Vol. xvii. p. 93. 



