133 
It is impossible to give a set formula prescribing the exact 
quantity of potassium cyanide to be used, owing to differences in 
the tightness of greenhouses. In those of average tightness I 
have used it on roses and cucumbers, without injury to them, at 
the rate of i ounce to 3000 cubic feet of space. 
The number of cubic feet in the house should first be accurately 
calculated. The method of doing this may be illustrated by a 
simple computation based on the dimensions given in the accom¬ 
panying figure, (Fig. 49) the understanding being that the length 
of the house is 100 feet. The cubic contents of the rectangular part 
of the house, a c d e, equals 24X6X100=14,400 cubic feet; that 
of the triangular part a b x equals 8X&X 100-^-2=3200 cubic feet; 
and that* of the other triangular part b c x, equals 8X 16X iocK-2= 
6400 cubic feet. The cubic contents of this house are, therefore, 
14,400+3200+6400=24,000 cubic feet. Assuming the house to 
be of no more than the average tightness, we may safely use the 
potassium cyanide at the rate of 1 ounce to every 3000 cubic feet 
of space, and 24,000 divided by 3000 (24,000-^-3000=8) gives 
the number of ounces required in this illustrative case. 
The next procedure is to get the materials in readiness for 
use, and to place the jars in the house. For every ounce of the 
potassium cyanide used, 2 ounces of sulphuric acid and 4 ounces 
of water are required. Two ounces of the cyanide is about the 
right quantity for each half-gallon jar, therefore for a house of 
the above dimensions 4 jars should be placed at equal intervals 
along the aisles, and the 8 ounces of cyanide divided into four 
equal parts, and each part put into one of the paper bags. These 
are used not only for convenience in handling the cyanide when 
placing it in the jars, but also because they slightly delay the 
action of the acid upon it, thus giving the fumigator ample time 
to leave the house before the reaction occurs. 
The jars being placed and the cyanide properly weighed and 
bagged, the next step is to close the ventilators in order to pre¬ 
vent all avoidable escape of the gas. The water—4 fluid ounces 
to each avoirdupois ounce of cyanide—is then placed in each jar, 
the sulphuric acid—half as much as of the water—is added, and 
as soon after as possible the bags of cyanide should be put into 
the jars and the house vacated immediately. Doors should be 
locked and labels posted indicating the danger. No one should 
enter the house until it has been thoroly aired by opening the side 
doors, and, if convenient, the ventilators also. It is best to fumi¬ 
gate in the evening, keeping the house closed until morning. I 
have never found a greenhouse so tight that the fumes would 
remain in it in dangerous quantity all night; nevertheless, it is 
safest to air the house well before entering. 
