716 JOURNAL OF THE ROYAL HORTICULTURAL SOCIETY. 



Longer life may be attained in two ways — by placing wood under such 

 natural conditions that decay becomes impossible, or by preserving the 

 wood in one way or another. 



After describing the anatomical structure of timber, the factors which 

 cause the decay of wood are considered. Though insects of various sorts 

 can do much harm, it is fungi which cause the greatest amount of de- 

 struction in timber — bacteria and some hymenomycetous fungi being de- 

 scribed and figured, and the process of decay by means of enzymes explained. 



The next section deals with timber preservation. The first method 

 was charring, the next was the use of preservative paints. Finally, the 

 injection of preservative substances into the wood was adopted. The 

 second was found ineffectual because the evaporation of water was pre- 

 vented, and gave access to any fungus -spores to grow. 



The materials for injection are copper sulphate (CuS0 4 ), zinc sulphate 

 (ZnS0 4 ), zinc chloride (ZnCl 2 ), mercuric chloride (HgCl 2 ), aluminium sul- 

 phate (A1 2 (S0 4 ) 3 ), and the products of coal-tar distillation. 



The object of the salts is to prevent decay by destroying fungi, and 

 the solution must be of a certain strength, as below a certain per cent, 

 the fungus can begin to grow, as bacteria and other destroying agents. 



The preservative must be of easy injection, and ought to remain per- 

 manently in the wood. It must penetrate all parts of the timber, and it 

 must be cheap. 



Then follow accounts of the results of timber impregnation in Texas 

 and in Europe, with technical details and figures on the structure of 

 railway ties, poles, &c, as well as on stacking. 



With regard to the methods of impregnation, the one used in England 

 Belgium, and France — the creosoting process — is the most costly, but at 

 the same time the most effective in preserving the wood. 



Tables show the final results as to ties which had to be removed within 

 twelve years, according to their being seasoned or not seasoned, and 

 treated with the various salts mentioned above. Thus zinc chloride in- 

 creased the length of life of Beech, which decays the most rapidly, more 

 than three times. After eleven years 82 per cent, of these treated witli 

 zinc chloride are still in service. Of Spruce only 49 per cent, were in 

 service. With Pine, copper sulphate gave better results than zinc chloride, 

 as the former had 16'5 per cent, and the latter 19*8 removal. 



Other comparisons are given for timbers used in Austria. Thus un- 

 impregnated Oak ties lasted on an average eleven years, while these treated 

 with zinc chloride were, for the most part, still in position after twelve 

 years, and of those treated with tar oil still more. 



With regard to creosoting in England, Scotch Fir will last twenty-five 

 or more years. The Bethell process is used, the injection resulting in a 

 complete impregnation of the sap-wood, with a small penetration of the 

 heart-wocd. This total impregnation of that part of the wood from which 

 decay usually starts retards the destruction of the timber for many years. 

 Such timbers as can be wholly impregnated with creosote will never rot. 



The various merits of the other salts used as injections are further dis- 

 cussed, as well as new processes, as the " senilisation by electric action," 

 " emulsion treatment," &C, but they have not yet been sufficiently tried. 



G. H. 



