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STATE HOETICULTUBAL COMMISSION. 



Hydrocyanic Acid Gas Treatment, for Destroying Scale Insects on 

 Citrus Trees. — This treatment should be used in the night so as 

 to avoid light, heat, and sea breeze, which neutralize the effect 

 of the gas. The chemicals used for producing the gas are: 

 Sulphuric acid (commercial), cyanide of potassium (98% to 

 99%), and water. 



The following instructions must be carefully observed: First, 

 the tent, which must be air-tight, is placed over the tree; 

 second, the tent is made air-tight around the bottom by 

 throwing some loose soil over the bottom of the canvas; third, 

 the necessary amount of sulphuric acid, together with the 

 required amount of water, is put in a glazed earthenware ves- 

 sel, and placed under the canvas, and the cyanide of potassium 

 is added. A piece of sacking or burlap is thrown over the top 

 of the vessel, to spread the gas and prevent it from burning 

 the leaves immediately above the generator. The tree is left 

 covered forty minutes. 



The Riverside County Board of Horticultural Commis- 

 sioners recommends the following proportions of chemicals: 



The cyanide should be used about the size of walnuts, so 

 that the chemical action will be less violent. The gas is also 

 generated more evenly, and there is not so much danger of the 

 chemicals boiling over or spattering the tent. As soon as the 

 tent is removed ^the vessel is rinsed with clean water and 

 prepared for another charge. 



APHIDS,:OR PLANT LICE. 



Next to the scale insects are the aphids, or plant lice, as they 

 are generally called; these also belong to the sucking insects. 



Plant lice are small, usually green, but varying to brown or 

 black insects, and are generally found on the under side of 



