84 TRANSACTIONS OF ROYAL SCOTTISH ARBORICULTURAL SOCIETY. 
from the receiver, the degree of the vacuum produced being shown 
by the gauge provided. The object of creating this vacuum is to 
exhaust the air from the pores of the wood, but it has no effect in 
extracting either natural sap or moisture in the wood. 
When the air has been exhausted as far as possible, which takes 
from fifteen to twenty minutes according to the sizes of the 
receiver and air-pump, the valve on the pipe leading to the air- 
pump is closed, and that on the pipe which communicates directly 
with the creosote tank is opened. The pressure of the atmosphere 
operating on the surface of the creosote forces it up the pipe, and 
completely fills the vacuum in the receiver. The valve on the direct 
pipe is then closed, and that on the pipe connecting with the force- 
pump is opened. This pump being set in motion, more creosote is 
driven into the receiver, but, as it is already filled, the pressure 
forces the oil into the pores of the wood. The force-pump is kept 
going until either the desired quantity of creosote has been injected 
into the wood, or until the safety valve, which is usually loaded to 
a pressure of 120 lbs. per square inch, begins to rise. When the 
safety valve rises, it may be due to the creosote being forced in 
more rapidly than it can be absorbed by the wood, or to the pores 
of the wood being filled by moisture, in which case the limit of 
absorption in the timber is quickly reached. 
The quantity of creosote injected into the wood is ascertained by 
noting the extent to which the level of the creosote in the storage 
tank falls during the time the force-pump is working. The size of 
this tank being known, the quantity of creosote represented by each 
inch of depth can readily be calculated. Thus, each inch of depth 
of a tank 12 feet by 8 feet would represent 50 gallons of creosote, 
and if there were 500 cubic feet of timber in the receiver, and it 
were intended that each cubic foot should be injected with one 
gallon, or 104 lbs., of oil, the foree-pump would have to be kept 
going until the depth of the creosote in the tank was 10 inches 
less than it was when the pump was started. The pressure is kept 
on for an hour or two after the desired quantity of creosote has been 
injected, then, the valve on the direct pipe being opened, the surplus 
creosote is drained back into the tank, after which the end door is 
removed and the timber withdrawn, and stacked till required for use. 
The usual works and appliances for creosoting are generally on 
a very large and costly scale. The writer has therefore designed 
asmall creosoting apparatus, represented on the accompanying Plan 
(see Plate XIII.), which is suitable for estate purposes, and costs 
