212 RAILWAY CONSTRUCTION. 



distilled from coal tar, varying in its composition according to 

 the quality of the coal from which it is obtained, and ranging in 

 its specific gravity from 11 'OS to 10'28. 



Creosote oils of light specific gravity were at one time in 

 favour, but experience proved that, to some extent, the light oils 

 were volatile and also soluble in water, and that heavy rains 

 washed out the constituents which were essential for the 

 preservation of the timber. On the other hand, by heating the 

 heavy oils and using high pressure the napthaline which is 

 dissolved only by the heat, is forced into the wood, fills the pores, 

 and solidifies. 



Creosote is obtainable in large quantities, at prices varying 

 from twopence to fourpence per gallon, according to the demand 

 and cost of production. Newly delivered sleepers or railway 

 timber contain so much sap or water that it is impossible to 

 force a sufficient quantity of creosote into them until they are 

 properly seasoned or dried. 



The seasoning is generally arranged by sawing each block 

 into two sleepers, and then stacking the sleepers on edge in tiers, 

 leaving a space of four or five inqhes between each of them for 

 a proper circulation of air. The sleepers should then be left for 

 nine to twelvemonths to season, although more may be necessary 

 in some cases if the blocks were particularly wet at the time 

 they were sawn. 



When ready for the process the sleepers are placed in the 

 creosoting cylinder, which is generally about 60 feet long by 

 6 feet in diameter with semi-spherical ends. One of the ends is 

 fitted with strong hinges and fastenings, and forms the doorway. 

 The sleepers are packed carefully inside, and the doorway made 

 tight. The machinery is then set to work to exhaust the air 

 from the cylinder and allow the creosote to flow in amongst the 

 sleepers. When the cylinder is full the force-pumps are started 

 to force in more creosote up to the pressure prearranged and 

 regulated by the safety-valve, in some cases 100, 110, or 120 Ibs. 

 per square inch. The creosote should be heated to 112 or 

 120 Fah., to dissolve the napthaline and reduce all the com- 

 ponent parts to a thoroughly fluid condition. 



The success of creosoting depends almost entirely upon the 

 effectual seasoning of the timber. Only a very small quantity 

 of creosote can be forced into wet or unseasoned sleepers, even 

 with the best machinery and exceptionally high pressures, while 



