METHODS OF INJECTION. 675 



In considering therefore the good results of the process of 

 injecting wood with chloride of zinc under steam pressure, it is 

 the process most highly to be recommended for Germany. 

 The question whether wood injected with metallic salts loses 

 strength and becomes brittle, requires further investigation, 



[As already stated, the objection to the use of metalHc salts for 

 injecting wood is chiefly that they are liable to be washed out by 

 rain, although they usually penetrate more deeply into the wood 

 than heavy tar-oil. There is a further objection to the use of 

 sulphate of copper or chloride of mercury, that they react injuriously 

 on iron, but this objection does not hold for chloride of zinc, which 

 appears to answer satisfactorily in a comparatively dry country, such 

 as parts of Germany. Mr. W. H. Preece* gives some interesting 

 facts as regards the durability of injected telegraph-posts in England. 

 In 1844, the line of telegraph between London and Southampton 

 was constructed with posts of best Memel timber Burnettised with 

 chloride of zinc ; and in 1857, the following per-centages of decayed 

 posts were observed : — 



On sand 40 per cent. 



On clay 33 „ „ 



Onchalk 28 „ „ 



In 1871, all the posts had to be removed. Unprepared telegraph- 

 poles last 7 years, Boucherised poles 15 years. In 1848, 318 poles 

 on a line of 20 miles from Fareham to Portsmouth were creosoted 

 by Mr. Bethell, and in 1883, every pole but two was sound. 

 On the South Western Railway along the line from Yeovil to 

 Exeter, in 1861, poles were put up alternately, as follows : first, 

 ail uninjected pole ; then, a Boucherised pole ; then, a creosoted pole, 

 and so on for 40 miles. In 1870, all the uninjected poles were 

 rotten, and 30 per cent of the Boucherised poles, while not one 

 creosoted pole had gone bad. 



Creosoted red-pine sleepers used on English railways appear to last 

 from 8 to 12 years, but much depends on the amount of traffic, 



Bouisson of the Western Railway of France statest that on the 

 line from Rouen to Dieppe, creosoted beech sleepers were laid in 

 1859, and in 1878 not one of them showed any signs of decay, though 

 beechwood unprepared becomes completely decayed in 2 or 3 years. 

 Granthamt also stated that on the Great Western Railway in England, 

 creosoted Baltic sleepers last 8 to 10 years and uncreosoted 5 years, 

 and that kyanised sleepers last 6 to 7 years. — Tr.] 



* Proceedings of Institution of Civil Engineers, vol. 78, p. 174. 

 + Minutes of Proc. of Inst, of Civ. Eng., op. cit. p. 659. 



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