1034 
Journal of Agricultural Research 
Vol. XXVIII, No. 10 
diameter through which the steam is allowed to escape into the kiln for a certain 
length of time, six hours for every inch of thickness of the lumber being formerly 
the period of steaming. Then dry heat is applied and the hot air rises through 
the lumber, cools, and settles toward the bottom of the kiln. The circulation 
is completed by air currents set in motion by spraj^s of water coming from jets 
about 18 inches apart, directed downward, on pipes along the sides of the kiln. 
These jets of water help to regulate the humidity. After the cool air reaches 
the bottom it passes through the pipes again where it is brought to a higher 
temperature. 
The temperatures in the following experiments were governed by a Taylor 
recording thermometer. This was controlled by placing a maximum ther¬ 
mometer in the kiln on the samples undergoing treatment. The relative 
humidity, as previously stated, was constant at 100. All temperatures were 
recorded in degrees Fahrenheit. 
PREPARATION OF SAMPLES 
The infested lumber was placed in a kiln which was kept at a low temperature 
(100° F.) for several days to determine if the powder-post beetles were still in 
the wood. 4 An examination of the material at the end of this time showed that 
it was still well infested. The presence of active larvae was shown by piles of 
boring dust, or powderlike frass, found on and about the pieces of lumber 
(PI. 1, A). 
The samples were prepared by sawing the ash lumber into boards 1 by 12 by 
18 inches and into planks 2 by 12 by 18 inches, making a total of 28 pieces of 
the former and 69 of the latter, and the oak into 4 pieces, each II by 12 by 18 
inches in size. The samples were divided into three lots as follows: 
Lot I. Ash, 7 pieces 1 inch thick and 14 pieces 2 inches thick; oak, none. 
Lot II. Ash, 12 pieces 1 inch thick and 6 pieces 2 inches thick; oak, 4 pieces 
II inches thick. 
Lot III. Ash, 9 pieces 1 inch thick and 20 pieces 2 inches thick; oak, none. 
These boards 1 and II inches thick and planks 2 inches thick were subjected 
to temperatures ranging from 120° to 160° F. and for different lengths of time. 
On account of the danger of running the thermostat at a temperature above 
160° F., the maximum at which it operates, and because previous experiments 
by C. C. Shackford had proved that this temperature is fatal to the powder- 
post beetles, no attempt was made to exceed it. 
The pieces were marked with their lot numbers and each was given an in¬ 
dividual number. The locations of piles of frass on the samples were marked 
with blue crayon (PI. 1, A, B). After the wood was removed from the kiln, 
these places were watched for signs of activity. Lot I was left in the kiln over¬ 
night at a higher temperature than that to which the material had been sub¬ 
jected previously. This caused increased activity and additional piles of frass 
were noted (PI. 1, A), proving that the samples were more heavily infested than 
previously indicated by the piles of frass on the outside. The proportion of 
sapwood and heartwood was also noted, as well as the depth of the larvae from 
the nearest surface. C. C. Shackford ran the kiln and assisted R. A. St. George 
with the work of inspection, 
PROCEDURE “ 
Each lot was treated by holding it at a certain temperature for a definite period 
of time before changing to a higher temperature, and removing pieces at every 
10° interval. At least one piece of each lot was examined by chopping into the 
4 Heating the material in this way was necessary because insects are normally inactive at the low tem¬ 
peratures of the falf and winter months. 
