2O6 DISEASES AND INSECT ENEMIES. 



cross-section paper cannot be obtained readily 

 the sections or squares can be laid off with a 

 rule and lead pencil and practically the same 

 results obtained. In any event, it is only neces- 

 sary to get an accurate outline drawing of the 

 section of the house and by projecting this over 

 squares as indicated the number of square feet in 

 the section can be readily determined. 



The gas is made by combining potassium 

 cyanide (ninety-eight per cent pure) and commer- 

 cial sulphuric acid. It has been found by experi- 

 ment that for violets 0.15 of a gram (one gram 

 equal fifteen and a half grains avoirdupois) of 

 ninety-eight per cent cyanide of potassium will be 

 required for each cubic foot of space in the house, 

 and from these data it is easy to figure out the 

 exact amount of cyanide of potassium wanted for 

 a given amount of greenhouse room. When the 

 cubic contents have been determined and 0.15 of 

 a gram of the cyanide of potassium has been 

 weighed out for each cubic foot, the next step is 

 to crush all the large lumps and place the cyanide 

 in paper bags so as to have it ready for use 

 in the house. We usually use two bags, one 

 within the other, for the purpose, in order to 

 insure perfect safety. For a house one hundred 

 feet long and twelve feet wide there should 

 be provided two ordinary earthenware jars, each 

 holding about two gallons. These jars should 

 be placed in the walk, about equal distances apart 



