288 INSECTICIDAL MATERIALS AND PRACTICES 



for every 100 cubic feet of space. Make the doors and windows 

 as tight as possible by placing strips of paper over the cracks. 

 Remove the silverware and food, and if brass and nickel work 

 cannot be removed, cover with vaseline. Place the proper 

 amount of the acid and water for every room in two-gallon jars. 

 Use two or more in large rooms or halls. Weigh out the potas- 

 sium 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 build- 

 ings, it is frequently necessary to suspend the bags of cyanide over 

 the jars by cords running through screw-eyes and all leading to a 

 place near the door. By cutting all the cords at once, the 

 cyanide will be lowered into the jars and the operator may escape 

 without injury. Let the fumigation continue all night, locking 

 all outside doors, and place danger signs on the house. 



Fumigation of greenhouses. 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 with- 

 stand the effects of the gas. Ferns and roses are very susceptible 

 to injury, and fumigation, if attempted at all, should be per- 

 formed with great caution. Fumigation will not kill insect eggs, 

 and thus must be repeated when the new brood appears. Fumi- 

 gate only on dark nights when there is no wind. Have the 

 house as dry as possible, and the temperature as near 60 as prac- 

 ticable. 



Fumigation of dormant nursery stock. Dormant nursery stock 

 may be fumigated in a tight box or fumigating house made espe- 

 cially for the purpose. Fumigating houses are built of two thick- 

 nesses of matched boards with building paper between, and are 

 provided with a tight-fitting door and ventilators. The stock 

 should be reasonably dry to avoid injury, and should be piled 

 loosely in the house to permit a free circulation of the gas. Use 

 one ounce of potassium cyanide for each 100 cubic feet of space, 

 and let the fumigation continue forty minutes to one hour. 



Fumigation of citrus trees. In this case the tree is covered 

 with an octagonal sheet tent made of 6J- ounce special drill or 8 

 ounce special army duck, and the gas is generated in the ordinary 

 way beneath it. The tent is so marked that when in position it is 



