156 
as an excellent fertilizer. Indeed, it is said that its value as a fer- 
tilizer alone is sufficient to cover its cost. 
For leaf -eating insects it is dusted on the leaves early in the 
morning, \vhile the dew is on. For root-feeding insects it is sprink- 
led along the rows at the base of the plants, preferably when the soil 
is moist. 
Dry Lime 
Fresh air-slaked lime or quicklime when used as a repellent for 
root-maggots is sprinkled along the rows close about the plants, and 
acts similarly to the carbolized-lime application. As some insects of 
economic importance are attracted to manures, the latter should be 
sprinkled over with lime where there is danger of infestation by in- 
sect pests. 
Dry lime, especially when fresh, is strongly caustic, and is there- 
fore valuable as a contact insecticide for slugs, plant-lice, and soft- 
bodied insects generally. 
Hydrocy.^nic Acid Gas 
Hydrocyanic acid gas is doubtless the most powerful and ef- 
fective fumigant known. Indeed, many are afraid to handle the 
deadly gas; but it can be used with perfect safety if proper care be 
taken. 
It is impossible to give a set formula for its use, owing to 
differences in the structure of greenhouses. In those of average 
tightness I have used it on cucumber plants, without injury to them, 
at a strength of i ounce of potassium cyanide to 3.000 cubic feet of 
space — fumigating in the evening, and keeping the house closed over 
night. 
The materials necessary for fumigation with hydrocyanic acid 
gas are potassium cyanide (98 to 99 percent pure), commercial sul- 
phuric acid, and water; and tlie requisite utensils are half-gallon or 
gallon jars — stone, earthen, or granite — and a supply of ordinarv 
small paper bags. 
Fig. 42. Diagram illustrating determination of cubic contents of 
greenhouse. 
