I'.ULLETIN NO. 'i2, MARCH, 1X95, 



105 



able success against the so-called Red Scale upon orange and lemon trees. 

 It is au expensive operation, but is unquestionably more thorough than 

 spraying. Trees infested with different kinds of x\spidiotus have been 

 entirely freed by a single ai)plication of this gas. 



The treatment consists in enveloping the tree in an air-tight tent 

 and afterwards tilling the tent with hydrocyanic acid gas, generated from 

 fused potassium cyanide, sulphuric acid, and water. This gas is much 

 lighter than air and as soon as generated rapidly rises, and fills the 

 tent. It is of course fatal to all forms of animal life, and care must be 

 exercised in using this treatment. The tent is usually constructed in 

 the form of au octagonal sheet, of what is ordinarily known as 8-ounce 

 duck, and is afterwards oiled with boiled linseed oil. A tent of this 

 kind, measuring 40 feet in diameter, will cost about $50, and other sizes 

 in like proportion. Almost any glazed earthenware vessel will answer 

 the purpose of a generator. The potassium cyanide used is usually of 

 (!0 per cent, strength and the sulphuric acid is of the ordinary commer- 

 cial brand. The proportions are, 1 ounce by weight of cyanide 1 fluid 

 ounce of the acid, and 3 Huid ounces of water. This is sufficient for 150 

 cubic feet of space inclosed by the tent. 



The water is first placed in the generator, the acid added, and after 

 the generator is placed under the tent the cyanide is added to the solu- 

 tion. The cost of the chemicals mentioned is small. The tree is sub- 

 jected to the action of the gas for about half an hour. In treating trees 

 10 feet high or less, the tent can be placed over the tree by hand, but 

 for those of greater height than this some sort of apparatus must be used 

 for the purpose of elevating the tent over the tree. An apparatus in the 

 form of a tripod, with a pulley at the top, serves this purpose very well. 



The following table of the relative amount of ingredients to height 

 and girth of tree top will be found useful : 



The best results will be obtained by treating the trees during the 

 •colder portion of the year or at night, as the gas is more liable to injure 



