352 NOTES ON DOCKS AND DOCK CONSTRUCTION. 



a powerful germicide, its efficacy ceases as soon as it evapor; 

 or is washed out of the substance intended to be preserved. It 

 cannot be considered a durable agent, particularly for piles and 

 other timbers used for harbour works. 1 



The apparatus required for the ordinary process of creosotm^ 

 consists of a wrought-iron cylinder usually of about 6 feet 

 diameter, and of a length sufficient to take in the longest 

 timber required to be treated. Ordinarily one end of the 

 cylinder is permanently closed, but a convenient arrangement 

 is to have both ends open, so that the timber may be entered 

 at one end and removed at the other. The ends are fitted with 

 strong cast-iron doors, by which they are hermetically closed. 

 A tank in close proximity to the cylinder to contain the 

 creosote, fitted witli an arrangement of steam-pipes for heating 

 the contents. An exhaust air-pump connected with the cylinder, 

 and a force-pump connected with both cylinder and tank, to- 

 gether with a suitable engine and boiler for efficiently working 

 the apparatus. The cylinder is fitted with rails to a gauge 

 corresponding with the roads extending through the timber- 

 yard. The timber to be treated is placed upon and firmly 

 secured to strong trucks, which are then run into the cylinder. 



In arranging the timbers on the trucks, care is taken to 

 keep them separate from each other by means of small pieces 

 of iron or wood, so as to admit of the free passage of the 

 creosote between them. 



The doors being hermetically closed, the air-pump is set 

 to work, and a vacuum created in the cylinder as complete as 

 possible, which is maintained for a considerable time, or until 

 all the air is extracted from the pores of the wood. 



The creosote heated to a temperature of about 120 Falir., 

 to bring the whole of the suspended and solid constituents into 

 a perfectly liquid condition, is then allowed to flow into tlu> 

 exhausted cylinder. When it ceases to flow freely of its own 

 accord, the force-pump is started to force more creosote into 

 the cylinder if required, and to raise the pressure to 150 11 is. 

 or 200 Ibs. per square inch. This pressure is maintained for 

 a considerable time, depending upon the character of tin- wood 

 under treatment, and the quantity of creosote per unit of 

 measure to be injected. 



The hygrometric condition of the timber at the time of 



M.r.I.C.E., vol. Ixxviii. pp, 113, 114 



