40 FRUIT TREES AND THEIR ENEMIES 



eggs which survived the first fumigation. For mealy 

 bug, this second fumigation should be done about a 

 fortnight after the first. 



The gas is a deadly poison, and operations con- 

 nected with it should never be left to the care of 

 workmen. It is made by acting on potassium or 

 sodium cyanide (also deadly poisons) with diluted 

 sulphuric acid. When stocks have to be fumigated, 

 they may be placed in a small greenhouse, or under 

 a skeleton box covered with oiled cloth. The 

 operation should not be done in sunshine, nor when 

 the temperature is above 60° F. ; also, the house, 

 earth, etc., should be as dry as possible at the time. 

 The amount of material used depends on the cubic 

 contents of the place to be fumigated : for every 

 100 cubic feet, two-thirds to one-quarter of an ounce 

 of potassium cyanide is required, or one-half to one- 

 fifth of an ounce of sodium cyanide, the quantity 

 depending on the hardiness of the plants treated. 

 For each ounce of cyanide, one liquid ounce of strong 

 sulphuric acid (oil of vitriol), previously diluted by 

 pouring it very gradually into 3 or 4 ozs. of water, 

 is required. A jar containing the diluted acid is 

 placed on the ground, and the cyanide, wrapped up in 

 a piece of netting or wire gauze, is lowered into it by 

 means of a string, passing over a pulley, or tied to a 

 long stick, so that the operator may work it while he 

 himself is outside the house. Every opening in the 

 house should previously have been closed, except the 

 one necessary for lowering the cyanide. After one 

 hour, the door may be opened, but no one should go 

 in, till time has been allowed for thorough ventilation. 



