324 
Journal of Agricultural Research 
Vol. XXXI, No. 4 
When all leads were installed the steam pan was placed on the 
area and preliminary temperatures were taken. The preliminary 
temperatures sometimes varied a degree or two, especially oh hot 
days, even though the soil was newly spaded. The surface soil 
would get warmed up considerably and tend to retain its heat long 
enough to show when the reading was made, even if it had been used 
to cover one of the lower leads and had later been covered by other 
soil. After preliminary temperatures were recorded, steam was 
turned on. The steam was always allowed to run wide open into 
the air for a few minutes to drive out any accumulated water of con¬ 
densation before the steam was turned into the steam pan. Some¬ 
times a number of gallons of water would be blown out, sometimes 
practically none would come out. During the time the steam was 
on and for an hour afterward temperatures were usually taken every 
five minutes. The steam pan was almost always left on for 30 
minutes after steam was shut off. 
Some Variable Factors 
The particular part of the pan area chosen for placing the bulbs 
did not seem to affect the results. The temperatures obtained with 
two bulbs at the same depth in different parts of the same pan did 
not always agree, but the variation was not constant for different tests. 
For a great many pan areas the percentage of moisture present 
in the soil was determined, but these data are not now available. 
Such data as are available, however, and the impression gained from 
observations at the time of steaming fail to indicate any particular 
correlation between the amount of soil moisture and the penetration 
of heat. In most cases steaming did not seem to greatly increase 
the soil moisture. Six samples from pan areas steamed for 40 
minutes and having moisture percentages ranging from 23 to 33 
and averaging 27 before steaming ranged from 25 to 50 per cent, 
averaging 32 per cent of moisture after steaming. This is an average 
increase of 5 per cent. If one sample showing an increase of 20 per 
cent (30 to 50 per cent) is omitted the average increase is only 2 
per cent. 
The increase in the percentage of moisture may depend on the 
type of soil more than on the quality of the steam. Of the six 
samples averaged, as indicated above, three were from the same 
pan area. In this case the soil was prepared as usual and three 
ditches scooped out for leads. In the middle ditch a single lead was 
installed, using the soil that had been removed from the ditch to 
cover the bulb and lead. In the left-hand ditch three bulbs were 
installed, yellow claylike subsoil being used to fill the ditch. In 
the right-hand ditch three leads were packed in black soil containing 
a large amount of fine fibrous rootlets and humus. In the normal 
soil the moisture increased from 25 per cent before steaming to 26 
per cent after steaming; in the clay soil the moisture was 33 per 
cent both before and after steaming; in the black soil the moisture 
increased from 30 to 50 per cent. The lead in the normal soil was 
buried to a depth of 4 inches. It showed a maximum temperature 
of 44° C. in 90 minutes. The 4-inch lead in yellow subsoil showed 
a maximum temperature of 55° in 90 minutes. The 4-inch lead in 
the black soil showed a maximum temperature of 61° in 65 minutes. 
Soil samples for moisture determinations were taken from 3 to 5 
inches below the surface in order to get soil more nearly representing 
