26 
The potassium cyanide used for producing the hydrocyanic acid gas 
is principally manufactured by two firms: Power & Weightman, of 
Philadelphia, Pa., and the Mallinkrodt Chemical Works, of St. Louis, 
Mo. That made by the first named firm is the most largely used ; when 
purchased by the ton the price is 36 cents per pound for the grade con- 
taining about 57 per ceit of pure potassium cyanide, packages and 
carriage extra. It is put up in tin cans holding 10 pounds each, and 
also in barrels holding about 400 pounds each. That in the cans is 
much to be preferred, since the quantity in each is so small that it will 
soon be used up after the can is opened; whereas, the barrel contain- 
jug so large a quantity, the cyanide used toward the last will have lost 
much of its strength by contact with the air. It is customary to weigh 
out the cyanide in small paper parcels, and mark each parcel with the 
number of ounces of cyanide that it contains; then when the tree is to 
be fumigated it is an easy matter for the operator to select one of the 
parcels containing a sufficient quantity of the cyanide for the tree, thus 
saving the trouble of weighing out the cyanide as it is to be used for 
each tree. As the fumigating is done only at night the weighing of the 
cyanide is frequently done by the ladies of the house upon the day pre- 
ceding its use. 
The quantity of cyanide to be used on each tree will, of course, de- 
pend not only upon the size of the tree but also upon the strength of the 
eyanide used. The following table will aid in determining the proper 
quantity of each ingredient to be used on different sized citrus trees, 
the cyanide being about 58 per cent pure: 
Height Diameter Sulphuric | Potassium 
of tree. | of tree-top. Water. acid. cyanide. 
Feet. Feet. Fluid ozs. | Fluid ozs. Ounces. 
6 4 3 4 A 
8 6 2 1 1 
10 8 43 24 24 
12 10 8 4 4 
12 14 16 8 8 
14 10 10 5 5 
14 14 19 9h 94 
16 12 16 8 
16 16 29 144 144 
18 14 26 13 13 
20 16 36 18 18 
22 18 52 26 26 
24 20 66 33 33 
Not only is this gas fatal to the Red scale (Aspidiotus aurantit Mas- 
kell), but also to the San José scale (Aspidiotus perniciosus Comstock), 
and indeed to all of the armored scales. It is also fatal to the Brown 
seale (Lecanium hesperidum Linn.) and to the Black seale (Lecaniwm 
olee Bernard), but the eggs of this species are not affected by it. 
The common Red Spider (Tetranychus telarius Linn.) and the Woolly 
Aphis (Schizoneura lanigera Hausmann) are also not affected by the gas 
when used strong enough to destroy the Red scale, although I have 
known it to prove fatal to true spiders (species not determined). House- 
flies (Musca domestica Linn.), Lace-winged flies (Chrysopa sp.?), and cer- 
