MECHANICS AND USEFUL ARTS. 49 



The use of timber upon our railroads is considered indispensable; it is 

 everywhere found in the superstructure of our tracks, and forms the chief 

 material of our bridges; its renewal is the most expensive item of repairs. 

 The life of a sill seldom extends beyond eight years, and the rate of annual 

 depreciation being 12 per cent., can be applied to the estimate for the dura- 

 bility of the bridges, and those structures which are unprotected against the 

 assaults of heat and moisture, the active and unfailing agents of decay. 



Upon the 25,000 miles of the railway lines in the United States, it is here 

 estimated that 3125 miles of the timber superstructure of their track are 

 annually renewed, requiring an outlay of $3,500,000 to furnish the supply. 



These prefatory data show the importance of seeking some effectual 

 method of arresting this enormous waste of capital. The chief obstacle to 

 this end has been the great outlay required in the outset for the apparatus 

 employed by the usual process, which is so inconvenient in character as to 

 preclude their adoption in the construction of our railroads. These objec- 

 tions of expense and inconvenience are applicable to the systems of Kyan, 

 Bethell, and Sir William Burnett, systems which have been adopted upon 

 the leading works of Europe, by engineers distinguished alike for their 

 genius and soundness of judgment. 



Kyan's process is the simple immersion of the timber in corrosive subli- 

 mate dissolved in water; it requires the employment of two tanks or reser- 

 voirs, into one of which the solution is pumped, while the timber is being 

 withdrawn. It has been severely tested in the dockyard of Woolwich, and 

 has been employed with success on the Bavarian state railways. The writer 

 has not been able to find any evidence against its efficacy. The solution is 

 an expensive one, besides being an active poison, which renders its adoption 

 dangerous. 



Bethell's process requires a strong cylindrical tank of iron, a steam-engine, 

 an air-pump, a force-pump, and a large wooden cistern or reservoir. When 

 the timber is placed inside the cylinder, which is air-tight, a vacuum is 

 obtained, and the solution, which is either coal-oil or pyrolignite of iron, is 

 forced, under a heavy pressure, into the timber. 



Sir W. Burnett's process employs chloride of zinc, with the same apparatus 

 and mode of operation used by Bethell. 



There has been a want of confidence relative to the treatment of timber 

 by other systems. The process of boiling timber, or heating it to a high 

 degree of temperature, and suddenly plunging it into the solutions, have 

 been condemned by the highest authorities. 



In the Ordnance Manual, for the use of the officers of the United States 

 army, edited by M:ijor Mordecai, it is stated that " kiln-drying is serviceable 

 only for boards and pieces of small dimensions, and is apt to cause cracks, 

 and impair the strength of the wood, unless performed very slowly; and that 

 charring or painting is highly injurious to any but seasoned timber, as it 

 effectually prevents the drying of the inner part of the wood, in which, con- 

 sequently, fermentation and decay soon take place. Boucherie also men- 

 tions his want of success in rarefying, by a regular heat, the air included in 

 the interior of the wood, and then plunging it at once into the solutions 

 which he wished to introduce, though by this method he caused diff rent 

 liquids to penetrate materials of a very compact nature; and li -n^-cc led 

 in forcing tar into stones and bricks to a very gre-it de)> h. 

 authority states "that it is infinitely more advantageous iu .... 



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