New York Agricultural Experiment Station. 203 



humidity. 



All who have had much to do with formaldehyde disinfection 

 recognize the importance of moisture. Numerous investigations 

 have shown that in order to insure efficient disinfection it is neces- 

 sary to have a comparatively high humidity. In the disinfection 

 of living rooms during cold weather this factor is a very important 

 one because in artificially heated rooms the relative humidity is 

 usually low and special methods must be employed to raise it. A 

 relative humidity of about 60 per ct. is usually considered the mini- 

 mum for thorough disinfection. According to Dudley and McDon- 

 nell it is the relative humidity rather than the absolute humidity 

 which is important. 26 



In the disinfection of seed potatoes the humidity factor has been 

 taken into account by Morse 27 who recommends that " just before 

 placing the formaldehyde in the generator the floor of the disinfect- 

 ing chamber should be thoroughly wet down with boiling water." 



Our own studies have dealt with the causes of tuber injury rather 

 than with the efficiency of disinfection, but it seems reasonable 

 to assume that anything which tends to increase the efficiency of 

 disinfection would tend to increase injury to the tubers. If so, 

 raising the relative humidity in the disinfection chamber might be 

 expected to increase the liability of the tubers to injury. As a 

 matter of fact, our experiments seem to show that such is the case, 

 but the evidence is not entirely conclusive. As no means were 

 employed for accurately controlling either the temperature or the 

 humidity, and the factors of quantity and germination were also 

 variable, the experiments were so much complicated that close com- 

 parisons are impossible. By an examination of Tables I and II 

 it will be seen that the relative humidity was rather high in all of the 

 experiments. The lowest maximum humidity was 73 per ct. in 

 Experiment 27. In the majority of the experiments the maximum 

 was in the neighborhood of 90 per ct. This may account for the 

 failure of the experiments to show marked effects from changes in 

 humidity. 



When small quantities of potatoes are treated the maximum humid- 

 ity is usually reached in from two to four hours after starting the 



26 Dudley, C. B., and McDonnell, M. E. Disinfection of passenger cars. Reprint 



from the American Engineer and Railroad Journal, June, 1902. 

 "Me. Sta. Bui. 174:325. 



