On the Preservation of Timber. 
11 
plained above, and which will be found fully described in the 
Appendix. 
Class VII. Compression. — A very different result is proposed 
to be accomplished by mechanical means by Billington, who 
employs suitable machinery to compress and consolidate the 
fibres of the wood, rendering it non-absorbent of moisture, and 
he dispenses with the use of creosote and all other preservative 
liquids. 
Sievier, on the other hand, first saturates the timber with any 
of the usual materials, and then submits it to powerful pressure. 
He states that the previous impregnation increases the compact- 
ness, and renders the wood more durable. 
Chemical Agents. 
Class VIIL Insoluble Albuminous Compound. — Having de- 
scribed the various mechanical means employed to fill the pores 
of wood with the different chemical substances which have been 
suggested, I must now briefly review these agents, and in the 
first class will be found those which act upon the albuminous 
matters. These chemical agents have generally a strong affinity 
for these azotised compounds, and when combined with them 
they become insoluble, inert, and not susceptible of those che- 
mical changes which ultimately lead to the destruction of the 
ligneous fibre. 
Tannin, — Among the most obvious, but not the first which was 
used, is tannin, patented by Newton so late as 1840. It acts in 
the same manner as when employed in the tanning of skins. 
The long duration of oak (in the sap of which it exists) under water, 
as well as the preservation of fishermen's nets, are due to its action. 
Tar Creosote, or Dead Oil. — Next in natural order come tar 
and all its derivatives, the value of which has long been recog- 
nised by the marine of all countries, but the first time they were 
employed for the preservation of railway sleepers only dates from 
Bethell's patent. They act in a similar manner to tannin, and 
are now generally acknowledged to be the most suitable material 
for this purpose. 
Corrosive Sublimate. — Then follow all the metallic compounds, 
among which the first employed was corrosive sublimate, or the 
bichloride of mercury, which formed the subject of Kyan's patent 
in 1832, and which had long been successfully used for the pre- 
servation of anatomical preparations. The high price, and the 
danger to which the workmen are exposed by its absorption, 
are objections which have weighed against its general intro- 
duction. 
Chloride of Zinc. — The chloride of zinc, patented by Burnett 
