IIO 
THE TELEGRAPH. 
often made of iron. Larch is stronger than the two other 
woods, but it is not so quickly saturated. The iron posts are 
the most durable. 
Kesinous trees have until now been preferred because the 
posts are easily and effectively prepared of a regular shape, and 
the cost is moderate. 
The posts are usually prepared between May and December. 
Trees cut between December and March having much thin sap 
can be injected with copper sulphate long after they have been 
felled; but the freezing of the preservative liquid, which usually 
happens from the winter’s cold, makes it impossible during that 
season to carry out Boucherie’s process. Among substances 
other than copper sulphate that have been hitherto used for 
preserving timber, we may place in the front rank creosote oil, 
which is obtained by distilling gas-tar. It is in general use 
for the preservation of the fir sleepers on railways, and in 
England it has been much applied to the preservation of 
telegraph posts. 
Unfortunately, as creosote has a powerful corrosive action on 
organic substances, it causes the handling of the posts to be 
attended by much inconvenience, for it destroys the workmen’s 
clothes and takes the skin off their hands and faces. Freshly 
prepared posts, moreover, have so very strong a smell as to be 
unsuitable for use near dwelling-houses. For these reasons 
the use of creosoted posts has been abandoned. 
Trials were made in Prussia of chloride of zinc as a preserva¬ 
tive, but in 1854 it was concluded that this substance could 
not be used advantageously, because it was liable to be dis¬ 
solved out by the rain. "While posts preserved by chloride of 
zinc keep very badly in calcareous soils, they last very long in 
sandy places. 
Iron Posts .—Iron posts are but little used in France, Eng¬ 
land and Belgium, except in certain ca^es. But in India no 
others are used, and they are common in Australia and South 
America. In these countries, where wood is very quickly 
destroyed by the ravages of the white ant, and where the 
ordinary preservative processes cannot be used on account of 
their expense, recourse is had to iron, and thus a great number 
of posts can be sent by sea in a small compass. 
Tubular posts of sheet iron have also been contrived. They 
