36 



present or not, only the strength of the fumigation, the time of day 

 and the time the house is closed differing in the one case from the 

 other. 



To fumigate an empty house, weigh the right amount of cyanide on 

 quite accurate scales. This amount should be known in ounces and 

 fractions of an ounce. Then, with such a measuring glass as is used 

 by druggists and photographers, measure out twice as many ounces 

 and fractions of commercial sulfuric acid as there were of cyanide. 

 Thus, if the amount of cyanide for the house, using an ounce to every 

 hundred cubic foot, was 3^ ounces as weighed on the scales, 6J ounces 

 of the sulfuric acid should be measured out in the measuring glass. 

 The water should now be measured out in the glass, taking twice as 

 much as was taken of the acid, or — in the example just given — 

 exactly 13 ounces by measure. From this it is evident that, starting 

 with the cyanide, twice as much sulfuric acid and four times as much 

 water are taken, the last two being measured, however, rather than 

 weighed. 



As a matter of convenience, it is easier to measure the water before 

 the acid, and put the water in the fumigating dish; then measure 

 out the acid and pour it very slowly into the water, to avoid the pro- 

 duction of much heat; then all that remains is to add the cyanide. 



Before doing this have all ventilators and other openings in the 

 house tightly closed, but so arranged that some of them at least can 

 be opened from the outside. If the house is not very tight, rags 

 should be forced into the cracks, an old case knife being often very 

 convenient for this purpose. Finally, when all is ready, the cyanide, 

 which should be in a very loose paper bag or on a piece of thin cloth, 

 should be taken, cloth or bag and all, and dropped into the dish, the 

 operator at once running as quickly as possible to an exit from the 

 house, which he must then close as tightly as possible. 



If no plants are in the house, the longer it is before the doors and 

 ventilators are opened the more certainly will all insects there be 

 killed. Several hours or even a day, then, is none too long for this 

 purpose, and the least time taken should be at least three hours. 

 When the fumigation has been completed, open the doors and ven- 

 tilators from outside, and let the house air for at least an hour before 

 entering it. The house may now be considered ready to start plants in. 



Where plants are already in a house, and fumigation is necessary, 

 the same general method is followed, but with a few changes. 



It has been found that fumigation in the day time is much more 

 likely to injure the plants than at night, though the reason for this 

 has not been discovered. Then different plants differ in the strength 

 of the fumes which they can stand without injury, and this must be 

 taken into consideration. In some cases if the gas be used strong 

 enough to kill all the insects present the plants will be seriously in- 

 jured, and it is necessary in such cases to use it weaker than is desir- 

 able, and repeat the fumigation oftener. 



Where a house is filled with but one kind of plant, the problem 

 how strong the fumigation can safely be made is much easier than 

 where many kinds are present. But just how much gas any plant can 

 stand under all conditions has not been ascertained, nor even whether 

 a strong treatment for a short time or a weak treatment for a long 

 time is the safer. For tomatoes it has been found at the Massachu- 

 setts Experiment Station that one-third of an ounce of cyanide to 

 every thousand cubic feet of house for forty minutes at night is safe 

 for the plants and quite effective against the white fly. In Maryland 

 three-fourths of an ounce per thousand cubic feet, the exposure to 



