74 
sucked through the timber by exhausting the air aud liquid from the 
cap. Square timber, even if of large dimensions, might thus be treated, 
the metal ring in that case being made of the same form as the section 
of the timber, and in dimension J or 1 inch smaller than that section. 
To effect complete saturation the fibers of the wood would have to be 
straight and parallel to the sides of the timber, but by applying the 
process to both ends a thorough impregnation of the inner portion of 
the timber would, in most cases, be obtained, while the parts near the 
surface would be impregnated by steeping. 
In describing at such length two processes which are not used, I have 
been influenced by the consideration that, while neither of them can ever 
find general application, there are undoubtedly locations and circum- 
stances in which preservation by a process requiring but slight outlay for 
plant is the only one feasible ; and, so far as I am aware, a full descrip- 
tion of these processes has never been furnished in any of the American 
publications treating on the subject of the preservation of timber. 
(3) Steaming. — When fresh timber is placed in a closed vessel and 
steam admitted into the latter, the first effect will be to expel the air, a 
tap provided for that purpose being left open. When the air has been 
driven out this tap is closed, and, more hot steam being admitted, the 
temperature of the timber and of the sap contained therein rises gradu- 
ally. When the temperature in any part of the timber rises to 167° 
Fahr., the albumen which is generally considered the ingredient in the 
sap most favorable to decay becomes solid. The air expands and a 
portion of it leaves the cells. The water contained in the cells is 
gradually transformed into steam, and the water of condensation, to- 
gether vfith a great portion of the extractive ingredients of the sap, is 
driven from the wood and collects at the bottom of the boiler, whence 
it is from time to time drawn off by a tap. The steam admitted should 
not have a pressure greater than about 20 pounds (corresponding to a 
temperature of about 260° Fahr.).* 
To coagulate all the albumen it is, of course, necessary that every 
part of the timber should be heated ; but heat enters rather gradually 
and slowly from the surface to the interior. Experiments made by in- 
troducing Rose's metal into holes bored into the timber from the surface, 
which afterwards were plugged, showed that after three hours' steam- 
ing, the heat required for coagulating albumen had penetrated only to 
a depth of 3 to 4 inches. It is evident, therefore, that if all the albu- 
men in the wood is to be coagulated the time during which the timber 
is steamed must be regulated according to its dimensions. 
With timbers of considerable length and of large cross-section, it may 
be necessary to continue the process for six and eight hours or more. 
* It would probably be even better to restrict the temperature of the steam to 
240°, or 10 pounds pressure, to prevent injurious effects to the strength, of the wood 
where bridge timbers are to be preserved, although the process would take more 
time. 
