358 
Journal of Agricultural Research 
Vol. XXXI, No. 4 
chemicals. The solution must contain 0.5 per cent of HgCl 2 in order 
to insure such penetration in Manor loam and in Leonardtown silt 
loam. 
The penetration of copper sulphate alone in solution is extremely 
poor. Penetration is somewhat improved by adding sodium sulphate 
to the solution, and greatly improved by adding five parts of sodium 
chloride to one of copper sulphate. The penetration secured was 
markedly less than that of the water of the solution even with solu¬ 
tions containing 2 per cent of copper sulphate. 
The penetration of kerosene is variable, increasing remarkably 
with increases in the percentage of moisture in the soil. Kerosene 
was used undiluted. 
The mercuric-chloride plus sodium-chloride solution was used in 
most experiments; the penetrations secured with applications of 1 
gallon per square foot were as follows: 
In potting soil, penetration, as shown by chemical tests, was er¬ 
ratic, probably owing largely to differences in the chemical makeup 
of different lots of soil. 
In Manor loam, penetration gradually increased from about 7 to 
8 inches in soil containing less than 5 per cent of moisture, to 8 to 9 
inches in soil with 17 to 19 per cent of moisture, and then decreased 
slightly in soil with 20 to 23 per cent of moisture. 
In Leonardtown silt loam, penetration gradually increased from 
6 to 8 inches in soil containing less than 5 per cent of moisture, to 
8 to 9 inches in soil containing 15 to 20 per cent of moisture, and to 
11 to 12 inches in soil containing 43 per cent of moisture. 
The effect of soil moisture on penetration is not the same for all 
chemicals. In Leonardtown silt loam, 1 gallon of HgC^ + NaCl 
solution and 1 gallon of kerosene penetrated to about the same depth 
in soil containing 1.8 per cent of moisture. In soil containing 19 
per cent of moisture, 1 pint of kerosene penetrated as deeply as 1 gal¬ 
lon of HgCl 2 + NaCl solution. 
With solutions of HgCl 2 + NaCl, the penetration obtained by 
applying 1 gallon of solution is less satisfactory than that obtained 
by applying the same amount of chemicals in % gallon of solution 
followed by K gallon of water. Other proportions of solution to 
water gave similar results. The actual depth of penetration was 
about the same, but the distribution of the chemical was more uni¬ 
form and the tests at points near the line of maximum penetration 
were markedly stronger where water followed the solution. 
The data obtained will be of assistance in planning field treatments 
and make it possible to determine in the laboratory the strength and 
amount of solution required for the effective treatment of a soil, 
taking advantage of favorable soil moisture or of rainfall and of 
cheaper methods. 
PART IV. POTATO GROWTH FOLLOWING CERTAIN CHEMICAL 
SOIL TREATMENTS 
As stated in Part I, many of the chemical treatments tested as 
possible means of exterminating potato wart resulted in more or less 
severe retardation of growth of potatoes. A summary of the growth 
of potatoes in the treated plots during three seasons subsequent to 
the treatments is given below. The data here recorded are for 
relatively strong chemicals used in large quantities. Weaker appli- 
