354 NOTES ON DOCKS AND DOCK CONSTRUCTION. 



7GO Fahr. These boiling points are, however, lowered by the 

 effects of a vacuum. He therefore raises the temperature of 

 the creosote to something over the boiling point of water. The 

 creosote is thus made the vehicle for conveying sufficient heat 

 to the timber to evaporate the water and sap contained in it. 

 The heat, being communicated through an oily medium, does not 

 injure the timber from which the water has been volatilized. 1 



A cylinder, similar to that used for the ordinary process, 

 but fitted with a dome on the top, to which is attached the 

 exhaust-pipe of the air-pump, contains the timber introduced 

 in the usual way. 



The exhausting process, instead of ceasing on the creosote 

 being passed into the cylinder, is continued, the creosote in the 

 mean time being raised to a temperature of about 230 Fahr. 

 The creosote is not allowed to rise quite to the top of the 

 cylinder, so that a clear space is reserved for the free passage 

 of the vapour extracted from the timber, and as a precaution 

 against the creosote being carried over into the exhaust- pipe. 



The exhaust is continued until all the water and sap con- 

 tained in the timber is extracted. By the aid of the high 

 temperature of the creosote and the air-pump in the form of 

 vapour, the pressure-pump is then applied in the usual way. 



The vapour drawn through the exhaust-pipe of the air-pump 

 is condensed by passing it through the coil of a condensing 

 apparatus, the resulting water being collected and measured in 

 a receiving tank. 2 



The quantity of creosote injected should exceed the quantity 

 of moisture extracted. With charges of very wet sleepers, Mr. 

 Boulton has withdrawn water equal in volume to fifty gallons 

 per load, and replaced it with an equal volume of creosote by 

 the action of the air-pump alone. 8 



An experiment made by Mr. Boulton on six fir sleepers 8 feet 

 11 inches by 10 feet 5 inches = 18*57 cubic feet, showed that 

 water to the extent of 120 Ibs. = to 6*45 Ibs. per cubic foot, was 

 extracted, yet the timber when removed from the cylinder after 

 completion of the process, weighed 155 Ibs. = to 8'35 Ibs. per 

 cubic foot more than when put in, thus proving that a total 

 quantity of 275 Ibs. of creosote, or 14'8 Ibs. per cubic foot, had 

 been injected. 4 



In England and Holland, for land purposes, the amount of 



> M.P.I.C.E., vol. Ixxviii. p. 126. 2 IfciV. Ibid. 4 Ibid., p. 206. 



