Aug. 15, 1925 
Soil Disinfection for Potato Wart 
357 
unsatisfactory. In newly prepared dry soil a considerable amount 
of penetration under an obstacle can be expected. The amount of 
chemical carried by the solution drawn under the obstacle may easily 
be insufficient to treat adequately so much soil. In field soil the 
upward flow of water is retarded by an obstacle with a consequent 
accumulation of moisture under it. It is doubtful if there would be 
an adequate flow of solution into this already moist soil. Thorough 
cultivation would tend to separate the obstacles from the moist soil 
underneath. Screening and treating soil would be expensive and 
should be avoided if possible. Further study of the effect of ob¬ 
stacles in soil to be treated should be made. It seems likely that 
treatments could be made effective without much trouble except 
where obstacles were larger than 2 inches in diameter or were very 
numerous. Enough soil contains large obstacles in quantity to make 
this a problem worthy of further study. Kerosene has such ability 
to penetrate that it might be useful for ground of this nature. 
In the soil-treatment experiments in the field, as in the penetra¬ 
tion experiments in the laboratory, the soil was newly cultivated or 
mixed so that the capillary tubes were broken up and the moisture 
content made uniform for all parts of the soil likely to be reached by 
the solution. In a few cases in the field formaldehyde seemed to 
make especially good penetration in soil that had been undisturbed 
for some time. The single set of 48 tubes used to test penetration 
in soil allowed to stand gave peculiar but encouraging results. Fur¬ 
ther experiments would be necessary to determine the effect of stand¬ 
ing under different conditions. If soil could be satisfactorily treated 
without cultivation an important item of expense could be eliminated. 
If cultivation were unnecessary, soil could be treated more easily, 
especially in the spring before ary enough to work or when wet dur¬ 
ing the summer, as it would be difficult to haul an outfit over soft, 
wet ground. 
Experiments to determine the effect of penetration on the toxicity 
of the solution to the pdtato wart organism were very encouraging. 
For the mercuric chloride plus sodium chloride solution the results 
indicated that any strength giving a positive test at the required 
depth, as shown by the hydrogen sulphide test, would be effective. 
No tests have been run with other fungicides. Of course, other fungi 
might require a greater strength of solution. 
SUMMARY 
Study of the penetration of chemicals in the soil is handicapped 
by lack of tests suitable for determining the presence of chemicals 
in soil or soil solutions. 
Schryver’s test was found satisfactory for formaldehyde, hydrogen 
sulphide for mercuric chloride and copper sulphate, and the charac¬ 
teristic odor for kerosene in soil solutions. 
The penetration of formaldehyde is apparently equal to that of 
the water carrying it in solution even in dilutions of 0.05 per cent of 
commercial solution. 
The penetration of mercuric chloride alone in solution is poor, 
but it has been found that the addition of sodium chloride at the 
rate of five parts of salt, by weight, to one part of mercuric chloride 
induces penetration usually equal to that of the water carrying the 
