On the Preservation of Timber. 
13 
of the pores of the wood with a solid substance, rendering the 
timber more rigid and suitable for such purposes as railway- 
sleepers. In some of these processes two solid bodies are 
formed, while in others one of the resulting compounds is 
soluble. 
Oxides of Tin and Copper. — The first patent secured in which 
this principle is recognised is that of Treffrj in 1838, who only 
soaked his wood in soluble salts of tin and copper, and pre- 
cipitated the metallic base by means of an alkali or alkaline 
earth. 
Sulphuret of Barium and Sulphate of Iron. — Then followed 
the patents of Payne in 1841 and 1846, whose name is gene- 
rally associated with this principle, and who employed pressure 
so that the decomposition was effected in the interior of the 
wood, and the object more effectually accomplished than by the 
previous patentee. M. VVattien adopted this principle in France, 
employing for his first liquid a solution containing 5 per cent, 
of sulphuret of barium, and following this with another liquid 
containing 5 per cent, of sulphate of iron, both under a pressure 
of 10 atmospheres. A double decomposition takes place in the 
pores and vessels of the ligneous tissue, by which two insoluble 
compounds were formed, namely, sulphuret of iron and sulphate of 
barytes, while an excess of sulphuret of barium remained to repel 
the attack of insects, the action of fermenting fluids, and the 
generation of mould. This mode of carrying out Payne's process 
communicates great rigidity and density to the sleeper. 
Various modijications of metallic Salts, ^c. — Halden has patented 
the use of sulphuret of calcium and chloride of zinc ; Jackson the 
use of sulphate of zinc and phosphate of ammonia ; and Kemp 
the use of sulphuret of barium and sulphate of copper. 
Soluble Silica and Acids. — Ransome proposed, in 1845, to imi- 
tate the petrifactive process of nature, by impregnating the timber 
with a solution of silica, and then immersing it in an acid or 
saline solution, so as to render the silica insoluble. He has since 
then suggested the use of chloride of calcium, or a solution of 
chloride or other soluble acid, salt of iron, copper, zinc, lead, or 
barium. 
Gutta Percha and Bisulphuret of Carbon. — A modification of 
this principle has been proposed by Assanti, who dissolves gutta 
percha in bisulphuret of carbon, which he forces into the timber, 
and then expels the volatile solvent, leaving the pores of the 
wood filled with gutta percha. 
Class X. Saline Solutions. Common Salt. — Of this class of 
chemical agents, common or sea-salt may be taken as a type, 
which is so universally employed in preserving meat, fish, skins, 
