212 Report on the Progress and State of Ajjplied Mechanics. 



23. Organic nmteruds of construction are of vegetable or of animal 

 origin, and ai'e generally fibrous, like wood and leather; but exceptions 

 to this are found in caoutchouc and gutta-percha. 



24. The available sources of timber have of late been much increased 

 by the discoveiy of the useful properties of the trees of various distant 

 and lately settled countries, — such as the various Eucalypti of Australia, 

 some of which are remarkable for size and strength. Central and South 

 America also, — Africa, Ceylon, and other tropical regions, possess many 

 timber trees remarkable for strength, diu-ability, and beauty, whose 

 properties have only recently become known to Em'opeans. On these 

 points, interesting information may be obtained from the report of 

 Captain Fowke, E.E., on the specimens of timber at the Paris Exhibi- 

 tion of 1855. 



25. In the treatment of timber, the points of principal importance 

 are seasoning and preservation. Seasoning, which consists in the 

 evaporation or extraction of the moisture contained in the timber, to 

 such an extent as to prevent warping or decay from the presence of that 

 moisture, used formerly to be effected by spontaneous drying in the 

 open air, and occupied from two to four years : and when attempts were 

 made to hasten the process, or to render it more effective by artificial 

 means, these consisted in steeping, boiling, or steaming, whicli saved 

 but little time, and weakened the timber. But within the last few 

 years it has been diseovei'ed, that by exposing timber to hot air in an 

 oven, it can be as completely dried in a few days as formerly in two, three, 

 or four years. An example of this process may be seen at the yard of 

 Messrs. E. Napier & Sons, at Govan. It is unnecessary to enlarge upon 

 the economy which it effects in time and money. 



26. The PEESEfiTATiON OF TiiiBEE, by filling its pores with antisep- 

 tic fluids, has occupied the attention of various inquirers for nearly half 

 a century. Amongst the earhest substances employed with success, 

 was a solution of sulphate of iron ; more recently, a solution of bichlo- 

 ride of mercury was employed, as well as various other metallic salts. 

 The satm-ation was at first effected by simple steeping, then by pro- 

 ducing a partial vacuum by the condensation of steam in a receiver at 

 one end of the log, while the pressure of the atmosphere forced the 

 solution into the vessels at the other end ; and lately, a method has 

 been invented of forcing the solution by hjalrostatic pressure into the 

 vessels at one end of the log, so as to expel the sap at the other end, 

 and saturate the log with the solution. Good success has attended the 

 use, as a fluid for preserving timber, of a kind of pitch-oil, called in 

 commerce " creosote," (although differing from the creosote of chemists), 

 which not only prevents decay, but repels the various animals commonly 



