THE PREVENTION OP POTATO SCAB. 91 



deep the tubers may be piled and still have the gas effective on 

 all. Until this is determined it would be best to pile not over 

 one foot deep. Bushel crates made on the open slat-work plan 

 make admirable containers, provided they are stacked up loosely 

 in the disinfecting room after being filled with potatoes. Shal- 

 low, slat-work bins could also be built one above the other. If 

 one has only a few bushels of seed to disinfect, a large box 

 tightly covered and provided with slat shelves might serve the 

 purpose. It would be better if the box had a small door at the 

 bottom which can be opened to introduce the disinfecting mate- 

 rials and then quickly and tightly closed. 



The process of generating the gas is very simple. For each 

 1000 cubic feet of space use 23 ounces of potassium perman- 

 ganate crystals and 3 pints of formalin. Place a large flaring 

 pan or pail in the center of the disinfecting chamber and spread 

 the permanganate evenly over the bottom. Pour the formalin 

 quickly over the permanganate, give the dish one rapid tilt to 

 make sure of thorough mixing, then leave and close the room 

 as quickly as possible. When first mixed no change is apparent 

 but soon a vigorous foaming and boiling is set up, hence it is 

 important that the dish used be of sufficient size to prevent run- 

 ning over. A broad, shallow dish like a dishpan has been found 

 to be more satisfactory than a deep one. "The dishes used need 

 not have sides more than 8 inches in height, but must have wide 

 bottoms. A good rule to follow in deciding on the size of the 

 dish to be used is to choose one whose bottom is such that it will 

 just be hidden from sight when the requisite amount of per- 

 manganate is poured in and evenly distributed." Tin or galvan- 

 ized iron dishes are better than earthern jars. The disinfect- 

 ing chamber should remain closed for 24 to 48 hours. The 

 amount of formalin recommended is three times as much and the 

 time of exposure several times longer than that recommended 

 for killing bacteria, but it will not injure the potato tubers in 

 the least. How much the amount of formalin used and the time 

 of exposure can be cut down and still be sure of destroying the 

 scab germs must be determined by future experimentation. 



The seed potatoes can be disinfected some little time before 

 planting provided they are not allowed to come in contact with 

 undisinfected bags, barrels, bins, tools, etc.. which have been 

 used for untreated potatoes. 



