THE DESTRUCTION OE WOOD BY FUNGI 377 



timbers, telegraph and telephone poles, and, indeed, structural 

 timbers of all kinds. 



A few years ago the United States Department of Agriculture 

 commissioned Hermann von Schrenk to visit Europe for the 

 purpose of studying the various processes employed for timber 

 impregnation. The results of von Schrenk's investigations are 

 embodied in an elaborate report, called " Decay of Timber and 

 Methods of Preventing it." * According to this report (in which 

 railway sleepers are more especially dealt with), in England, 

 Belgium, and France the creosoting process is the one chiefly 

 used. Although it is the most costly, it is found to pay best in 

 the end in these countries. In Germany and Austria a cheaper 

 process, making use of zinc chloride and tar oil, is now employed, 

 whilst in some other lands the still cheaper zinc chloride process 

 finds favour. In England and France engineers believe that 

 their system gives the best results, and they use as much of the 

 impregnating material as the timber will hold. The extra first 

 cost of the sleepers is amply paid for, as their life is increased 

 by many years. Creosoted pinewood sleepers, in some cases, 

 have lasted twenty-five years or more. Timber wholly im- 

 pregnated with creosote never rots, but may be worn out by 

 mechanical abrasion. The advantage of using zinc chloride and 

 coal tar in conjunction is supposed to be that the coal tar pre- 

 vents the leaching out of the zinc chloride. When the latter is 

 used by itself, it disappears from the sleepers in course of time. 



About ten years ago a process of wood preservation known 

 as the Hasselman treatment 2 was developed. Salts injected 

 into wood are soluble in water, and hence liable to leach out. 

 The Hasselman treatment is supposed to cause the injected salts 

 to form an insoluble compound with the wood cell-walls. The 

 timber to be treated is put into a closed cylinder, and a solution 

 of copper sulphate, iron sulphate, aluminium sulphate, and a 

 small amount of kainit is run in. By means of superheated 

 steam the solution is brought to boiling-point. The timber is 

 boiled in the solution for several hours. The advantages of the 

 process lie in the cheapness of the salts employed, the rapidity 

 of the process, the fact that the wood to be treated may be wet 

 or dry, and also that the iron and copper salts penetrate every 

 fibre of the wood and form insoluble compounds with the wood 



1 U.S. Department of Agriculture, Bureau of Plant Industry, Bull. No. 14, 1902. 



2 H. von Schrenk, loc. cit. p. 55. 



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