26 



The potassium cyanide used for producing the hydrocyanic acid gas 

 is principally manufactured by two firms : Power & Weigh tman, 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 cent 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- 

 ing 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 

 cyanide 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 



Water. 



Sul ph uric 



Potassium 



of tree. 



of tree-top. 



acid. 



cyanide. 



Feet. 



Feet. 



Fluid ozs. 



Fluid ozs. 



Ounces. 



6 



4 



| 



i 



i 



8 



6 



2 



1 



1 



10 



8 



H 



21 



2i 



12 



10 



8 



4 



4 



12 



14 



16 



8 



8 



14 



• 10 



10 



5 



5 



14 



14 



19 



n 



9| 



16 



12 



16 



8 



8 



16 



16 



29 



14 h 



14£ 



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 Ped scale (Aspidiotus aurantii Mas- 

 kell), but also to the San Jose scale (Aspidiotus perniciosus Comstock), 

 and indeed to all of the armored scales. It is also fatal to the Brown 

 scale (Lecanium liesperidum Linn.) and to the Black scale (Lecanium 

 olecu Bernard), but the eggs of this species are not affected by it. 

 The common Eed Spider (Tetranychus telarins 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 (Ghrysopa sp.?), and cer- 



