PROTECTING PLANTS 189 



and dwellings for such pests and vermin as become established 

 in them. The following directions are from Cornell Bulletin 

 283 (from which -the formulas in the succeeding pages, and 

 most of the advice, are also taken) : — 



" No general formula can be given for fumigating the different 

 kinds of plants grown in greenhouses, as the species and varieties 

 differ greatly in their ability to withstand the effects of the gas. 

 Ferns and roses are very susceptible to injury, and fumigation 

 if attempted at all should be performed with great caution. 

 Fumigation will not kill insect eggs and thus must be repeated 

 when the new brood appears. Fumigate only at night when 

 there is no wind. Have the house as dry as possible and the 

 temperature as near 60° as practicable. 



" Hydrocyanic acid gas is a deadly poison, and the greatest 

 care is required in its use. Always use 98 to 100 per cent pure 

 potassium cyanide and a good grade of commercial sulfuric 

 acid. The chemicals are always combined in the following 

 proportion: Potassium cyanide, 1 oz.; sulfuric acid, 1 fluid 

 oz.; water, 4 fluid oz.- Always use an earthen dish, pour in 

 the water first, and add the sulfuric acid to it. Put the required 

 amount of cyanide in a thin paper bag and when all is ready, 

 drop it into the liquid and leave the room immediately. For 

 mills and dwellings, use 1 oz. of cyanide for every 100 cu. 

 ft. of space. Make the doors and windows as tight as pos- 

 sible by pasting strips of paper over the cracks. Remove the 

 silverware and food, and if brass and nickel work cannot be 

 removed, cover with vaseline or cloths. Place proper amount 

 acid and water for every room in 2-gal. jars. Use two or more 

 in large rooms or halls. Weigh out the potassium cyanide in 

 paper bags, and place them near the jars. When all is ready, 

 drop the cyanide into the jars, beginning on the top floors, 

 since the fumes are lighter than air. In large buildings, it is 

 frequently necessary to suspend the bags of cyanide over the 

 jars by ccy-ds running through screw eyes and all leading to a 



