IMPREGNATION 



181 



A train of railroad lies ready for impregnation at the works of the 

 American Creosoting Co. 



V. Use of steam pressure. 



The wood, thoroughly air-dried, is placed on small steel cars running into long cylinders to be sealed 

 hermetically by strong heads. If still partially green, the wood is dried, to begin with, by a steaming, 

 heating, or vacuum process. That done, an antiseptic liquid, at a temperature of 150 to 200 degrees, is 

 pressed by the force pumps into the wood. 



(a) The liquids commonly used ARE:^ 



1. Chloride of zinc. 



2. Coal tar creosote or heavy oil of 

 coal tar (commonly designated as 

 creosote). 



3. Mixture of chloride of zinc and of 

 creosote. 



4. Gases of tar oils (so-called thermo- 

 carbolization). 



5. Heavy petroleums. 



(b) APPLICATION: -The creosoting method 

 is used for ties, pilings, and paving blocks, 

 particularly. Creosoted timber holds nails well; 

 creosote is not washed out by rain. On the 

 other hand, the darkened color of the wood 

 is sometimes objectionable, and the cost of a 

 thorough impregnation is high. In the case of 

 telephone poles, the volatile character of the 

 lighter coal tar oils is found objectionable. 



The heavier portions of the coal tar oils are the most durable and the most effective. 



(c) Variable effects: -The impregnability of timber seems to depend on its specific we:ght and 

 on its contents of moisture; and does depend, undoubtedly, on many other factors not fully understood today. 



The oaks show greater fluctuations in absorption of creosote than do the pines. Variable is, also, 

 the distribution of the impregnating liquid within the wood impregnated. With the same quantity absorbed, 

 one railroad tie may be impregnated to a depth of 3 inches and another- of the same weight and kind — 

 to a depth of 1 inch only. 



The cost of tie impregnation, in America, is given as 30 cents per tie impregnated with an average 

 of 2' ,, gallons of creosote. 



The pressure in the impregnating retorts must be gauged according to the season of the year, according 

 to the degree of moisture in the wood, and according to the particular structure of the pieces to be treated. 



(d) Creosote oil : -The quantity of creosote pressed into the wood is obtained either from gauge 

 readings in the creosote tank, or else by comparing the weights of the impregnated ties with those of the 

 unimpregnated ties, adding to the difference, however, the weight of the water evaporated from them and 

 collected separately. 



As regards the composition of the creosote, the following specifications hold good:- 



"The creosote oil used must be the product obtained entirely from coal gas or coke oven 

 tar, containing no admixture of any tar, oil or residue obtained from petroleum or any other source. 



It must be completely liquid at 38 degrees centigrade, and not more than 2 per cent of the 

 water-free oil should be insoluble in chloroform or in benzol. 



The specific gravity of the oil at 38 degrees centigrade must be at least r03 and should not 

 exceed I'lO. The distillate of the creosote oil used shall deposit, between 210 and 235 degrees 

 centigrade, naphthaline salts upon cooling to a temperature of 20 degrees centigrade. During 

 distillation the oil shall not show any evidence of decomposition. 



The oil shall not contain more than 3 per cent of water." 



