204 Report of the Department of Botany of the 



generator, and then there follows a marked decline. When the 

 initial humidity is below 80 per ct. there is usually a sudden rise of 

 15 to 25 per ct. owing to the water vapor produced by the evapora- 

 tion of the formaldehyde solution. McClintic 28 has expressed the 

 opinion (based on the results of some of his experiments) that the 

 moisture given off by the evaporation of the formaldehyde solution 

 does not answer for disinfection purposes so well as the natural 

 humidity in the atmosphere. The writers have observed nothing 

 which indicates that this is true for tuber injury nor does there seem 

 to be any reason why it should be so. Both chemically and physically 

 the water vapor produced by the evaporation of formaldehyde 

 solution is the same as that in the air. 



When large quantities of potatoes are treated the maximum 

 humidity is not usually attained until at or near the end of the 24- 

 hour period. This is probably due to the influence of the moisture 

 produced by the respiration of the tubers. 



While the general trend of the relative humidity is as stated above 

 there are frequent exceptions. Changes in temperature, of course, 

 affect the relative humidity considerably and as the disinfection 

 chamber was not perfectly gas-tight changes in the humidity of the 

 outside air, also, had some influence. 



Although convinced that a comparatively high relative humidity 

 is necessary for the successful disinfection of seed potatoes by means 

 of formaldehyde gas the writers consider it unnecessary to wet 

 the floor with boiling water as recommended by Morse or to employ 

 any other means to increase the humidity. In cellars and store rooms 

 suitable for seed potatoes the humidity is naturally high, particularly 

 in the spring when the treatment is made. In addition to the natural 

 humidity the evaporation of the formaldehyde solution may be 

 expected to supply from 15 to 25 per ct. and the respiration of the 

 tubers, also, furnishes a considerable amount of moisture. As a 

 matter of course, an artificially heated room would not be used for 

 a disinfection room and in almost any unheated room the humidity 

 may be expected to be ample for the purpose of disinfection. 



Experiments made by Jones and Morse 29 indicate that the gas 



28 McClintic, T. B. The limitations of formaldehyde gas as a disinfectant. Pub- 



Health and Mar. Hosp. Ser. U. S. Hyg. Lab. Bui. 27:110. 1906. 



29 Vt. Sta. Rpt. 17:401. 



