Aug. 15, 1925 
Soil Disinfection for Potato Wart 
341 
tion of a soil organism the minimum penetration is the important 
figure and also that owing to the time and labor involved tests were 
necessarily made only by inches. 
In Table VIII the data are arranged to show the number of tubes 
giving positive tests at various depths each day. The daily increase 
in the proportion of positive tests at lower depths is very marked in 
the dry soil. The proportion of positive tests at 6 to 7 inches and 
at 7 to 8 inches is 1 : 2 at the end of the first day, becomes 1 : 4 in 
two days, 1 : 8 in three days, and 1: 13 at the end of five days. 
At the same time there is a marked increase in the number of posi¬ 
tive tests at 8 to 9 inches. The proportions do not change so widely 
and regularly at the other soil moistures, but the change is quite 
marked. 
Penetration op Mercury in HgCl 2 +NaCl Solutions in Leonardtown 
Silt Loam 
Penetration of HgCl 2 + NaCl solutions in Leonardtown silt loam 
was studied in the same way as penetration in Manor loam and sim¬ 
ilar tabulations of the data obtained are given in Tables IX and X. 
As in the Manor loam, the penetration in the drier soil averaged 
about 7 inches, this depth only being exceeded by part of the tubes 
where the application was made 1 + 1, that is, the chemicals were 
applied in half the water and an equal amount of water was applied 
later. The penetration in soil containing 8 to 15 per cent of mois¬ 
ture averaged 8 inches or a little more, only slightly less than the 
average penetration in soil containing 15 to 21 per cent of moisture. 
Penetration in soil containing 43 per cent of moisture was extremely 
rapid as well as approximately 3 inches deeper than in soil contain¬ 
ing 21 per cent or less of moisture. Of the 34 tubes, 21 gave positive 
tests for mercury in the solution that percolated through the tubes, 
and 7 gave positive tests in the bottom inch of soil. Ihe figures 
given therefore do not represent the absolute maximum of penetra¬ 
tion for such wet soil. As in Manor loam, the maximum penetra¬ 
tion was usually not obtained in less than three days, and depth of 
penetration did not seem to be particularly affected by applying the 
chemicals in part of the water and then applying the remainder of 
the water. 
In Table X the penetration data are arranged to show the number 
of tubes giving positive tests at each depth on successive days after 
the solutions were applied. The successive increases in the propor¬ 
tion of positive tests at lower depths are not so marked as in the 
Manor loam, although it is evident, particularly in the soil containing 
8 to 15 per cent of moisture. 
DISCUSSION OF PENETRATION OF HgCl 2 +NaCl SOLUTIONS 
Effect of Soil Type and Soil Moisture 
A comparison of the data in Tables VII and IX shows slightly 
better penetration in air-dry Manor loam than in air-dry Leonard¬ 
town silt loam. In Manor loam containing 10 to 16 per cent mois¬ 
ture the penetration was practically the same as in Leonardtown silt 
loam containing 8 to 15 per cent moisture. In Manor loam penetra¬ 
tion was better in soil containing 17 to 19 per cent moisture than in 
soil containing 20 to 23 per cent moisture. In Leonardtown silt loam 
61911—25f-4 
