No. 4.] GREENHOUSE PESTS. 391 



cial sulfuric acid and water, besides a dish or dishes considerably 

 larger than is needed to hold these materials, are necessary. The 

 dishes must not be of metal, though granite ware, if without any flaws 

 inside, will prove satisfactory. Earthen crocks or jars are often used, 

 and answer well for the purpose unless the heat produced by mixing 

 the sulfuric acid and the water causes them to crack, which sometimes 

 happens when the two are mixed too rapidly. 



Before fumigating, the number of cubic feet in the house (not count- 

 ing out the space taken by plants and benches) must be known, and 

 in many cases to calculate this has puzzled those in charge. The best 

 way to get this is to draw the house in cross-section, and then divide 

 this into squares and half squares or rectangles, as shown in the dia- 

 gram, which is drawn to the scale of a half inch to a foot. In this 

 diagram, the dotted lines show how the house plan has been divided 

 and the measurements of each part are given. The area of block 



V. 



No. 1 would be 24 feet (3 by 8) ; that of No. 2 would be so little over 

 9 feet that the fraction may be ignored (5 feet 4 inches by 3 feet 5 

 inches, and the answer divided by 2, only half of the rectangle being 

 present); that of No. 3 would be very slightly over 3 feet; while that 

 of No. 4 would be 3 feet. The entire number of square feet in a cross- 

 section of the house, then, would be 39. If this be multiplied by the 

 length of the house inside in feet, the number of cubic feet will be the 

 result. 



Fumigation to ensure that no insects are in an empty house can and 



