Aug. 15, 1925 
Soil Disinfection for Potato Wart 
323 
reducing valve or “pressure-regulator” was secured. A small gauge 
was put on near the end of the line of pipe and the reducing valve 
placed between this gauge and the steam main was set so that the 
gauge would read 10 pounds with the line wide open. While sudden 
calls on the main for hoisting, or other work in the mines sometimes 
made the pressure drop to 7 or 8 pounds for a moment, the steam 
flow was practically uniform for the entire period of steaming. By 
this method the steam could always be regulated in a few minutes, 
whereas formerly it usually took a half-hour or more. A measure of 
the quantity of steam flowing into the steam pan is essential for 
comparative purposes and to secure the uniform treatment of the 
different pan areas supposed to receive the same treatment. Where 
the pressure on the main or boiler varies, or where the outlet must 
be regulated to keep the boiler pressure up, even an approximate 
estimate of the steam flow is difficult. In such cases the use of an 
inexpensive reducing valve will do much to insure the delivery of 
uniform quantities of steam in a given time. 
The gardens used in our experiments are located at the southern 
boundary of the glacial advance, the soil being a mixture of the 
DeKalb and Volusia series of silt loams. The soil in these gardens 
was the usual conglomeration of soil, coal dust, and debris found in 
the gardens of coal miners in that region. As might be expected, the 
soil often varied considerably in different parts of the same garden 
and even in different parts of the same pan area. 
Electrical resistance bulbs were used to obtain the temperatures 
in soil under the steam pan. These resistance bulbs were connected 
to a Wheatstone Bridge on which the dial was graduated to show 
temperature in degrees Centigrade instead of showing the correspond¬ 
ing electrical resistance. The writers can not recommend these bulbs 
for this work, as they get out of order too readily when held at ap¬ 
proximately 100° C. 
Soil to be given a steam-pan treatment was spaded, and if lumpy 
the lumps were broken up, yielding a surface layer of well-cultivated 
soil 8 to 9 inches deep. When .temperatures were to be taken, one 
or more trenches were dug in this prepared soil and the leads placed 
in them and covered. The depth of the soil over the leads was 
measured by laying a board across the trench and measuring from 
the lower edge of the board to the top of the cap or bulb on the end 
of the lead. If the depth was not that desired more soil was added 
or some scooped out until the bulb rested at the proper level. By 
carefully removing the soil after the treatment was finished and re¬ 
measuring the depth to some of the bulbs it was determined that the 
method of placing the bulbs was accurate. In thus putting in the 
leads and getting them at exactly the right level it was usually 
necessary to add a layer of rather fine soil. In addition, the extra 
handling tended to break up the soil somewhat so that the soil sur¬ 
rounding the leads was undoubtedly finer than the main body of 
soil to be treated. The soil was not compacted. The leads were 
put in approximately parallel to the surface, so that the channels 
inevitably formed where the soil was in contact with them probably 
had little or no effect on the results obtained. Sometimes several 
leads were put in the same trench at different levels. When this was 
done care was taken to keep the bulbs from being placed one imme¬ 
diately over the other, even though 2 or 3 inches of soil might 
intervene. 
