336 Report of the Horticultural Department op thbi 



body. Exposing it to hydrocyanic acid gas kills it if the fumiga- 

 tion is properly done. Too great an amount of the gas will injure 

 the plant. If the gas is too weak or the time of exposure too 

 short, the scale insects may not all be killed. It is very impor- 

 tant, therefore, that the work be done only by intelligent and 

 careful workmen. ' . 



DANGER to HUMAN LIFe! 



But there is a still stronger reason for keeping this work 

 always under the direction of a competent person, and that is 

 because hydrocyanic acid gas is most deadly poison. One full 

 breath of it may at once stop the action of the heart. A large 

 dose may cause instantaneous death. 



THE CHEMICALS. 



Water, sulphuric acid and potassium cyanide are the chemicals 

 needed for making hydrocyanic acid gas. 



/Sulphuric acid (H2SO4). — A good grade of commercial sul- 

 phuric acid should be used. Its specific gravity should not be 

 less than 1.82. At present it costs less than two cents a pound, 

 wholesale. Care should be used not to spill the sulphuric acid 

 upon either the clothing or the person. It eats the clothing and 

 burns the flesh. 



Potassium cyanide (KCN). — The fused cyanide 98 to 99 per ct. 

 pure should be used. It is now supplied by the manufacturers 

 in wholesale quantities for about 30 cents per pound. Somewhat 

 higher prices are quoted by dealers. It is a white, solid sub- 

 stance, which absorbs moisture and gradually vaporizes unless 

 it is kept from the air. It is best to keep it in air tight cans, 

 plainly labeled "poison," and put where children or others who 

 may not know its deadly character cannot get it. 



Potassium cyanide is one of the most poisonous suhstances known! 



Instances are on record where adult persons have been killed by 



five grains, which would make a lump about the size of a large 



-pea. The vapor from the can in which potassium cyanide is 



kept is also poisonous. 



