Aug. 15,1925 
Soil Disinfection for Potato Wart 
329 
in the temperature of soil under the steam pan varied from 1° C. in 
0.17 minute to 1° in 19 minutes; the rate of decrease in temperature 
for the periods during which data were recorded varied from 1° in 
2.5 minutes to 1° in 107 minutes; the maximum temperatures reached 
varied from 100° to 29°; the maximum temperatures maintained for 
30 minutes varied from 100° to 28°. The variations in each case 
depend on the pressure of the steam used, the length of the treatment, 
and the depth in the soil. 
PART III.—THE PENETRATION OF SOIL FUNGICIDES 
INTRODUCTION 
Chemical soil disinfection necessarily implies contact between the 
sterilizing agent and the organism whose destruction is desired 
throughout its vertical distribution. Some chemicals, such as cop¬ 
per sulphate, are adsorbed or removed from water solutions before 
penetrating soil more than 2 or 3 inches. Other chemicals, such 
as bichloride of mercury, react with the soil chemicals and rapidly 
lose their toxic character. If the approximate penetration ability 
of chemicals were known, much unnecessary work would be avoided, 
since it would be possible to eliminate field tests of chemicals that 
would not penetrate the soil and to use only such strengths and 
quantities of other chemicals as would be reasonably sure to pene¬ 
trate to a sufficient depth. Moreover, if a chemical failed to pene¬ 
trate soil readily but had other merits, it might be tested by working 
it into the soil. 
An examination of the chemical literature available and consulta¬ 
tion with chemists failed to disclose the existence of the needed data 
on the soil penetration of chemicals. Simple tests for use in deter¬ 
mining the depth of penetration of possible fungicidal chemicals were 
next sought. 
Many fungicides are complicated compounds. The actual chemi¬ 
cal state of the effective element in these compounds is not always 
known. In the case of these and of some of the simple compounds 
the tests in common use may be for one of the elements making up 
the compounds. Positive tests might then be obtained, even though 
the nature of the compound had been changed by reactions with the 
soil and its effectiveness lost. In other words, the writers did not 
know whether or not the tests available could be depended on for 
use in soil solutions. For many of the compounds with which the 
writers wished to experiment, no test, or at least no usable test, was 
available. Any test requiring prolonged individual attention would 
not be usable. The possession of penetration data offered such possi¬ 
bilities of increased efficiency in the prosecution of the soil steriliza¬ 
tion studies that it seemed desirable to investigate the subject as 
thoroughly as possible, in spite of the difficulties involved. 
HISTORICAL 
Heretofore soil sterilization work has been largely confined to the 
control of seed-bed and greenhouse diseases ana under specific con¬ 
ditions. Little data on the amount of penetration obtained are 
given in the reports. Gilbert (4), in speaking of formaldehyde 
sterilization of tobacco seed beds for Rhizoctonia and Thielavia root 
rot, recommends drenching the soil with formaldehyde, using 1 
part of formaldehyde to 150 to 200 parts of water, three-fourths to 
