161 



For piles, jetties, and other marine works, 10 Ibs. or 1 gall, per cubic foot. 



Oak does not readily take up more than 2 or 3 Ibs. of creosote, and teak more than 

 If per cubic foot. 



According to Molesworth, the relative absorbing power of timber, Memel pine being 

 assumed = 1, is : elm = 1*35 ; yellow pine = 1*15 ; beech = - 4 ; English oak = '34. 

 And the results of the Cape " tests of Yellowwood for Railway purposes " reduced to 

 yellow pine = 1*15 give : Outeniqua Yellowwood = 2'60 ; Upright Yellowwood = 

 2'44 ;" dry open grained Baltic sleeper" = 2'20 ; white pear = T08. 



b. Chloride of Zinc process. 



The impregnation of timber with a solution of zinc chloride is effected in the 

 same apparatus, and in the same manner as with creosote ; but steaming up to 150 may 

 take place if the wood is not already well seasoned ; after which, the liquid that has 

 collected at the bottom of the cylinder is drawn off, and the exhaustion of the air, com- 

 menced. The pressure used in Germany for impregnation with chloride of zinc is 

 usually 112 Ibs. to the square inch. 



The solution consists of one part of the commercial chloride of zinc solution to 50 

 parts of water. Formerly the proportion adopted was 1 in 30, but it was found that the 

 iron spikes became corroded. The commercial zinc solution contains 25 per cent, of 

 metallic zinc, equal to 52'4 per cent, of chloride. It is diluted to the proper strength for 

 impregnation with the aid of densimeters graduated from I'OOO to 1*100. 



The quantity of zinc chloride taken up is about '2 Ib. per cubic foot for oak, and 

 *5 Ib. per cubic foot for beech and pine-wood. Drying the wood before pickling is not 

 necessary. 



The pneumatic process with zinc chloride gives results almost equal to creosoting, 

 while its cost is only from one-half to one-third. This process is regarded with increasing 

 favour, and in Germany it is now the one most largely followed for the impregnation of 

 railway sleepers, 



c. Boucherie's process. 



The timber is impregnated with a 1 per cent, solution of copper sulphate, 

 placed in a tank 30 to 40 feet from the ground, giving a pressure of 13 to 17 Ibs. per 

 square inch. A watertight cap is fitted on one end of the log to be treated, and the solu- 

 tion from the tank being introduced by means of a flexible tube, drives out the sap 

 through the log and takes its place. This process can only be applied to timber freshly 

 cut and with the bark left on. It has been chiefly used for the impregnation of telegraph 

 poles of round wood. The quantity of sulphate taken is about '3 Ib. per cubic foot. 



d. Pneumatic sulphate of copper process. 



The apparatus used is similar to that required for creosoting. The impregnating 

 fluid consists of a 2 per cent, solution of copper sulphate, 1-5 to 1'8 galls, of which are 

 forced per cubic foot, equal to "30 to '36 Ib. of sulphate. The solution is usually heated 

 to 120, and a pressure of 60 to 120 Ibs. per square inch maintained for at least half-an- 

 hour. To test the result, a 9 per cent, solution of potassium ferrocyanide is used ; a drop 

 of this reagent placed on the wood should give it a red stain ; a pink stain denotes that 

 the impregnation is not sufficient. 



e. Hot immersion, 



The wood is kept for two hours in tanks containing a 2 per cent, solution of 

 copper sulphate, heated by means of steam pipes to 140 ; the impregnation is only 

 effected to a small depth. 



f. Kyanizing. 



This consists in impregnating the wood with a solution of mercuric chloride 

 (corrosive sublimate), of a strength of 0'66 per cent. The quantity of the salt taken up 

 is *066 Ib per cubic foot. Mercuric chloride is the best antiseptic known, but the 

 difficulties in the way of its application, resulting from the fact that the solution cannot 

 be placed in vessels of common metals, and its great cost, make other substances to be 

 preferred for the preservation of timber. 



g. Payne's process. 



The wood is impregnated first with a strong solution of ferrous sulphate, then 

 With a solution of barium sulphate ; the wood is rendered incombustible, but a slow 

 destruction of its fibres appears to take place. 



