6 BULLETIN 518, U. S. DEPARTMENT OF AGRICULTURE. 
and this fact should be considered where an assortment of plants 
is to be fumigated. In case there is any doubt as to the amount 
of gas a plant will stand without injury, it is preferable that the 
initial dosage be not over one-fourth ounce of sodium cyanid per 
1,000 cubic feet and increased with subsequent fumigations until 
the fatal point of the pest to be controlled is reached, it being borne 
in mind that in some instances it is not possible to effect an abso- 
lute control of all stages of some insects with one fumigation with- 
out injury to foliage or growing parts of certain plants. For ex- 
ample, the greenhouse white fly has been eradicated with three suc- 
cessive fumigations at intervals of 7 to 9 days, using one-half ounce 
of sodium cyanid (NaCN) per 1,000 cubic feet, in houses containing 
such susceptible plants as coleus, ageratum, heliotrope, fuchsia, etc., 
with no injury to the foliage. Moreover, such resistant pests as scale 
insects can be eliminated entirely by killing the immature stages with 
‘a small dosage repeated at frequent intervals. 
Under favorable conditions houses which do not contain roses, rose 
geraniums, asparagus ferns, lemon verbena, snapdragon, Wandering 
Jew, or sweet peas can be fumigated vith safety with an initial 
dosage of one-half ounce of sodium cyanid (NaCN) per 1,000 cubic 
feet. 
To determine the total amount of cyanid to be used, ascertain from 
the tables on pages 12-18 the plants in your greenhouse which are most 
easily injured by the gas fumes and note the amount of cyanid which 
was used per 1,000 cubic feet with little or no injury to the plants. 
Then multiply the number of thousand cubic feet contained in the 
house by the amount of cyanid to be used per 1,000 cubic feet. For 
example, if one-half ounce of cyanid is to be used per 1,000 cubic 
feet, and the house contains 15,000 cubic feet, the total amount of 
cyanid necessary would be 74 ounces. 
In case there is any doubt as to the amount of gas the plant can 
stand without injury, the initial dosage, as previously stated, should 
not exceed one-fourth ounce per 1,000 cubic feet. 
CHEMICAL FORMULA -TO BE EMPLOYED. 
The chemicals! should be mixed in the following proportions: For 
each ounce of sodium cyanid use 14 fluid ounces of sulphuric acid and 
2 fiuid ounces of water. 
11f potassium cyanid is used in place of sodium cyanid, the formula should be ag 
follows: For each ounce of 98 to 99 per cent potassium cyanid containing 38.4 per cent 
cyanogen use 1 ounce of sulphuric acid and 3 ounces of water. The yield from 1 ounce 
of high-grade sodium cyanid is equivalent to the yield from 1% ounces of high-grade 
potassium cyanid. 
