Aug. 15, 1925 
Soil Disinfection for Potato Wart 
335 
to secure percolation of the water through the tubes. Using this 
preliminary data as a basis, laboratory tests with formaldehyde were 
planned. 
The first tests were made with six brass tubes in series. The 
tubes were filled and then compacted with the compactor for metal 
soil tubes. The column of soil was usually 143^ inches deep after 
compaction. Just enough solution was supplied to keep it at the 
overflow level in all tubes. The time was recorded when solution was 
turned on the tubes and again when percolate began to drip from the 
bottom of each tube. The percolate was tested for formaldehyde 
and gave a strong positive test in each case. Three strengths of 
formaldehyde were used, viz, per cent, M per cent, and 1 per cent. 
The rate of percolation in air-dry (3 to 4 per cent moisture) Manor 
loam soil varied from 7.8 to 11.4 minutes per inch, averaging 9.6 
minutes per inch for the 23 tubes used. The rate of percolation in 
potting soil was much more rapid. Six tubes of potting soil with 
3.13 per cent of moisture showed percolation at the rate of 4 minutes 
per inch. Six tubes with 11.3 per cent moisture showed percolation 
at the rate of 3 minutes per inch. 
Penetration of Copper Sulphate 
In tests with 1 per cent copper sulphate solution in potting soil 
(6 tubes) containing 7.6 per cent of moisture the average rate of per¬ 
colation was 4 minutes per inch. With a 2 per cent solution of cop¬ 
per sulphate, using Manor loam (6 tubes) containing 6.3 per cent of 
moisture, the rate of percolation averaged 11 minutes per inch. No 
positive test for copper was secured in the percolate from any of 
these tubes. 
Penetration of Alcohol 
Alcohol, 47 per cent, in one test with six tubes of potting soil con¬ 
taining 4.45 per cent moisture, showed percolation at the rate of 6.5 
to 9.5, averaging 8 minutes per inch. The percolate gave positive 
tests for alcohol in each case. 
Penetration of Qua-sul 
Qua-sul, a proprietary sulphur compound, was tried at 1 per cent 
strength on six tubes of potting soil with 8.7 per cent moisture. Per¬ 
colation was at the rate of 3.8 to 8.8, averaging 5.3 + , minutes per 
inch. No sulphur could be precipitated in the percolate. The pot¬ 
ting soil used was taken from the mixing bench. 
If variations in the make-up of the soil in different tubes was 
responsible for the wide variations in rate of percolation, these varia¬ 
tions in composition did not show in a casual examination of the soil. 
Amount of Solution Required for Percolation 
The amount of solution required to percolate through the tubes of 
soil was determined from the increase in weight. The tubes were 
weighed dry and again after the percolate started to drip, but with¬ 
out allowing the soil to drain. The increased weight in grams was 
assumed to equal the number of cubic centimeters of water held. 
The maximum amount of solution held by any one of 30 tubes of 
potting soil was 300 c. c., the minimum 227 c. c., the average 258 
c. c. The maximum amount of solution held by any one of 17 tubes 
