88 TRANSACTIONS OF ROYAL SCOTTISH ARBORICULTURAL SOCIETY. 
per cubic foot. Timber of this class should therefore remain in 
the cylinder under pressure for twenty-four hours. 
Various modifications of the creosoting process have been pro-— 
posed. Some of the softer woods have been treated by being 
dried and then immersed in hot creosote in open tanks for a time, 
but this has not always proved successful. Mr H. Aitken, of 
Falkirk, introduced a process in 1882, in which the timber was 
soaked in melted naphthaline for a period of from two to twelve 
hours, according to its bulk. With the view of getting the 
creosote to penetrate the wood as thoroughly as possible, its 
iatroduction, first in the form of a vapour, followed by the injec- 
tion of the oil itself in the ordinary way, has been tried, but the 
method has been abandoned. As the solutions of metallic salts, 
mentioned earlier in this paper, penetrate the heart-wood of well- 
grown timber much more readily than creosote, the experiment 
has also been tried of impregnating the wood with a salt solution, 
and afterwards creosoting the outer portion, to keep the salt from 
being washed out. Some American authorities consider that a 
compound process of this kind gives better results than creosoting 
alone. 
The most important modification which has been intrcduc>d is 
that patented in 18729 by Mr 8S. B. Boulton, Assoc. Inst. C.E., 
by which the moisture in the timber is got rid of during the 
creosoting process, so that newly felled or wet timber may be 
treated. In this method the creosote, after being introdaced into 
the receiver, is raised to a temperature slightly exceeding the 
boiling point of water—212° Fahrenheit. By this means, the 
water in the timber is volatilised, and drawn off by the air-pump 
in the form of vapour, and the creosote takes its place. The heat, 
being communicated through an oily medium, does not injure the 
timber. The vapour may be passed through a condensing ap- 
paratus, and collected, when the quantity extracted can be 
measured. With charges of very wet sleepers, Mr Boulton has 
succeeded in extracting water equal in volume to 1 gallon per 
cubic foot, and replacing this water with an equal volume of 
creosote by the action of the air-pump alone. If necessary, the 
force-pump can be afterwards applied in the usual way. 
The apparatus is of course more costly, and a good deal of 
additional time is required for dealing with wet timber by this 
process; but its advantages are very great in those cases in which 
time for seasoning the timber cannot be given, or where storage 
