IMPREGNATION OF TIMBER -WITH ANTISEPTIC SUBSTANCES. 235 



The raised end of the log is sawn oif with a clean section and 

 covered with the cap (c), which consists of a square board and a 

 ring of tarred rope placed between it and the log. The cap is 

 pressed up against the log by the dog-bolts dd, the free ends of 

 which pass through the batten b and are fitted with screw nuts, 

 An oblique hole (h) is bored, into which is inserted the nozzle of a 

 gutta-percha tube connected with the elevated reservoir of antisep- 

 tic liquid. The reservoir is placed about 30 feet above the ground 

 in order to secure the required pressure of one atmosphere. Un- 

 der this pressure the liquid drives before it the sap in the wood. 

 At first, the pure sap riins out at the other end of the log in a con- 

 tinuous trickling stream. Later on, the sap is mixed with the 

 antiseptic substance, the proportion of which of course increases as 

 the sap remaining in the log diminishes, until no more sap is left 

 and only water containing the antiseptic substance oozes out. To 

 ascertain whether the wood is sufficiently impregnated, chips are 

 removed from it from time to time and examined. The impregna- 

 tion is complete before the liquid that runs out of the log is of the 

 same strength as the solution in the reservoir. 



The process is very considerably shortened by impregnating at 

 once logs of double the required length. In this case the log is 

 sawn through the middle for about three-quarters of its thickness. 

 It is then raised in the middle so as to make the cut gape open and 

 a piece of tarred rope is let in along the circumference. On letting 

 go the log, the sides of the cut close tightly upon the rope, and 

 form with it a completely water-tight chamber, A single oblique 

 hole with inserted tube sufiices to impregnate both halves of the 

 long log. Fig. 74 renders the preceding explanation clear. 



Fig. 74. 



Mode of impregnating two lengtJis of log in a single operation. 



To prevent waste of the antiseptic substance, the fluid that runs 

 out from the free ends of the logs falls into gutters g, whence it 

 flows away into the cistern ci at the bottom of the platform. From 

 this, the liquid, after being made up again to full strength and, if 

 necessary, freed from organic matters, is pumped up into the re- 



