20 



SOME FUNGOUS DISEASES OF ECONOMIC IMPORTANCE. 



This unit has been used throughout the experiments. McClintic a 

 found that the percentage yield of formaldehyde is not much affected 

 by variations in temperature when the experiments are performed 

 at temperatures above 60° to 65° F. He also proved that successful 

 disinfection varies directly with the humidity. The fumigating box 

 was placed in a room which was provided with an automatic tempera- 

 ture and ventilating apparatus, thus permitting a perfect control of 

 atmospheric conditions. The humidity in the room was found to be 

 fairly constant during all the experiments, the average relative 

 humidity being 38 per cent. 



The formalin used was purchased in the open market and was sup- 

 posed to be of 40 per cent strength, but on analysis it was found to 



Fig. 3. — Sketch showing a sectional view of the interior of the fumigating box with the 



psychrometer attached. 



contain 37.97 per cent of formaldehyde by weight, with a specific 

 gravity of 1.0669 at 20° C. Chemically pure potassium permanganate 

 in finely divided crystals was employed. In each of the experiments 

 the formalin used was in the proportion of 100 c. c. to 50 grams of 

 permanganate. 



Preliminary experiments were made with cultures of the fungus 

 in petri dishes, Van Tieghem cells, and test tubes, with quantities of 

 formalin ranging from 300 to 1,200 c. c. per 1,000 cubic feet of space, 

 to determine the approximate quantity of the gas fatal to Thie- 

 laviopsis. It was soon demonstrated that quantities of formalin less 

 than 700 c. c. per 1,000 cubic feet were ineffectual in prohibiting the 



McClintic. Op. cit. 



171 



