,SO/L DISINFECTION 



57 



used if desired. The steam should be kept at as high a 

 pressure as possible, 80 to 100 pounds being best, and the 

 treatment should continue for one or two hours, depending 

 on the pressure maintained. In experiments conducted 

 on tobacco seed beds in the spring of 1907, one hour's 

 steaming at 80° C. gave best results in killing both the fungi 



Fig. 18. — Disinfecting soil with a Sargent disinfector. Original. 



and the weed seeds. When one section of the bed is 

 treated, the pan is lifted and carried to another portion, and 

 the operation repeated until the entire bed is steamed. 



The Sargent method. — Disinfection by a system of 

 steam pipes arranged in the form of a harrow, with hollow, 

 perforated teeth, has proved satisfactory under some 

 conditions. 



Surface firing. — Surface firing of seed beds has been a 

 common practice for years in some tobacco sections, par- 



