Aug. 15,1925 
Soil Disinfection for Potato Wart 
325 
the average. The surface soil was, of course, always damp or wet 
when the pan was removed, but lost much of this excess moisture 
within a few hours. 
An attempt was made to determine the temperatures in undis¬ 
turbed soil by inserting the leads in horizontal holes made by driving 
a rod in from a trench along one side of the soil to be treated. It 
did not seem possible to place the leads accurately enough in this 
way to get results that could be averaged without running a large 
number of tests. The results obtained did not seem to indicate 
that any marked differences in temperatures would be found be¬ 
tween the newly spaded and the unspaded soil. If this should be 
found to hold true under all conditions it would obviate the necessity 
for cultivating the soil before steaming it. 
DISCUSSION OF TEMPERATURES OBTAINED 
A summary of the more important data obtained is given in 
Table V. A considerable number of tests are not included in this 
summary because the leads were placed at other depths, or because 
the temperatures were not taken for a long enough time, or because 
something went wrong with the apparatus before the series of tem¬ 
perature readings was complete. Hence the small number of figures 
averaged does not necessarily measure the real value of the data. 
In any event the data given represent a great advance over those 
hitherto available. 
In Table V, temperatures obtained at 1, 4, and 7 inch depths only 
are considered. The data from the different pressures and lengths of 
steaming are arranged to show the maximum temperatures obtained 
the number of minutes taken to reach that temperature, the tempera¬ 
tures recorded at different times afterward, the last temperature 
taken, the length of time elapsing after the maximum temperature 
was reached until the final temperature was taken, the rate at which 
the temperature increased from the initial to the maximum tempera¬ 
tures (given in minutes elapsing for each degree of rise in tempera¬ 
ture) , the rate at which the temperature declined from the maximum 
to the last temperature recorded (given in minutes elapsing for each 
* degree of fall in temperature), and the “maximum sustained tem¬ 
perature” arrived at by averaging the temperatures that will give the 
highest average for a half-hour period (the table showing the minimum 
temperature used in securing this average as well as the maximum 
and average temperatures). The number of sets of figures averaged 
for each line of figures given in the table is shown in the column at 
the extreme right. 
The table of temperatures (Table V) has been made sufficiently 
complete to enable anyone to make curves showing the rise and fall 
of temperatures for each treatment and depth considered and showing 
the amount of heat received by each depth, as indicated by these 
temperatures and the elapsed time, over a period of three or four 
hours. The maximum sustained temperatures and the pressures and 
times necessary to attain them, with which the results of treatments 
given may be correlated, are perhaps the most important figures for 
potato-wart work. The data as a whole may be of considerable value 
to others, particularly perhaps to those engaged in a study of the 
biological changes induced by steam-pan treatments of the soil. 
