76 
and when the latter is filled with the liquid, force pumps are empioyea 
to force the solution into the cells of the wood under a pressure of 100 
to 150 pounds. The pressure is kept up until, on stoppage of the pumps, 
it remains nearly constant ; say from three to sixty hours, according to 
quality, kind, and dimensions of the timber. 
The cars with the timber on them are then removed from the boiler 
and a new charge introduced. 
Note. — Many seem to be under the impression that the effect of the vacuum in draw- 
ing out the sap and air is unlimited, and the same as regards the pressure in forcing the 
preservative into and through the wood. We have no doubt that the vacuum and pres- 
sure are of great benefit, but to what extent the complete impregnation of the wood is 
affected by the) amount of air that may be in the wood-cells remains to be settled by 
farther investigation, and more precise inforinatiou would be useful. In green and 
rafted tiinher the sap is in a more or less liquid form, and the log may thus be so full 
of moisture as tp contain a minimum amount of air, and steaming can be of benefit 
only by making the sap more fluid, the moisture of the steam being of no advantage. 
The heat also expands what air there is in the wood and thus drives out some of the 
moisture. With such timber it probably would be better to apply dry heat rather 
than by direct steaming, and thus add heat without extra moisture, for if wo get a 
stick of timber thoroughly water-soaked, the wood-cells are full of water and there 
is no place into which to force the preserving fluid. — H. C. 
ANTISEPTICS USED IN THE PRESERVATION OF WOOD. 
'Ortt of the great number of substances which, during the last sixty 
years, have been proposed for preserving wood from decay, or rather 
for prolonging the period of its usefulness, only four have stood the test 
applied, and are now employed for that purpose. 
1st. Heavy oil of tar (creosote ofl, dead oil). 
2nd. Bichloride of mercury (corrosive sublimate).* 
3rd. Chloride of zinc. 
4th. Sulphate of copper. 
In addition to these some substances are employed for preventing the 
gradual removal of these antiseptics from the wood by exposure to at- 
mospheric influences, such as chloride of tannin, glue, tannin, and 
sulphate of lime. 
(1.) Heavy Oil of Tar. — The heavy oil of tar is the product of the dis- 
tillation of coal-tar between the temperatures of 480° and 7G0° Fahr. 
It generally contains from 5 per cent, to 10 per cent, of cresylic acid, 
the remainder consisting of heavy oil and naphthaline in varying pro- 
portions. An analysis of tbe "oil, as imported from England and used 
at the works at Slidell, La., gavefl.75 per cent, of carbolic and cresylic 
acid, 12.50 per cent, of naphthaline, and 77.75 per cent, of heavy oil. 
At 65° Fahr. it weighs about 9 pounds per gallon, and boils at a temper- 
ature of 265°. It has great antiseptic qualities, and being insoluble in 
water, has the advantage over all other substances used for the preser- 
vation of wood, in that when applied in proper manner, it forms a coating 
