2 . Insecticides and Fzmgicides. 21
. potassium and sulphuric acid. When fumigating it is well
  to place a notice on the room or house warning people not to
?$ enter. i After the fumigating is accomplished it is advisable
i to open up doors and windows and air out for ten minutes or '
more before entering. V
  The dose to be used depends on the space to be fumigat-
_ ed and upon the character of the plants to be treated. Dor-
  mant trees, can be exposed for a time to very strong fumes. "
. Growing plants must be treated cautiously with very mild
p doses. Some -of them are very sensitive to the gas and will
· be slightly burned with any dose calculated to be of value in
destroying insects. The condition of the air as to moisture
may influence the results, since dampness favors injury from
T the gas.
For nursery stock it is customary to employ for each 100
L, cubic feet enclosed, the following:
Cyanide of potassium . 1 ounce
l . Sulphuric acid » . . 1.25 fluid ounces
i Water .... 3 fluid ounces
}_ The box or house should be as nearly gas-tight as possi-
ble, with a very tight—fitting. door. The water and sulphuric
l acid are placed in a` deep open crock, then the cyanide of
l _ potassium, broken up into pieces about as large as a hickory
I nut, is poured into the crock and the door shut as quickly as
i possible. The fumes must be left about the trees not less
. than forty minutes, and fifty minutes, or an hour, is better.
l‘ Short exposures in badly constructed houses have sometimes
  resulted in the sending out of living San Jose scale on trees.
In the hothouse the gas must be used with very great
l care to avoid injury to plants. Plants of the grass family
j (Gramineae) endure more gas than most others tested by me.
1 Corn, timothy, blue-grass and the like, are not very sensitive.
' The leguminous plants, such as clover, sweet pea and cowpea `
' are very likely to suffer some injury with any but very light f
_ doses, and on this account it is best to use the less hurtful
tobacco extract when practicable. The extract will not, how-