42 THE NURSERY-MANUAL 



Heavy canvas or burlap, 216 square feet. 

 A steaming pan to cover an area of about 72 square feet. 

 Attachments for the steaming pan, consisting of 4 ring bolts 6 

 inches long, with 3-inch rings; 4 bars or ax handles; felt packing 

 2 inches wide, sufficient in length to extend around the pan; the 

 same length of 4-inch hoop iron or of 2-inch angle iron ; one f -inch 

 nipple 6 or 7 inches long, threaded on both ends ; two f -inch leather 

 gaskets ; two f -inch nuts or threaded washers. 



"The boiler is the item of greatest expense, the rest of the equipment 

 being comparatively inexpensive. With proper care the entire apparatus 

 should last for a number of years. 



"A boiler of sufficient capacity is the essential factor in successful 

 sterilization, because large volumes of high-pressure steam are required. 

 Experience has shown that a boiler of at least 20-horsepower is necessary 

 for efficient steam production when using a steaming pan of the size men- 

 tioned above. In some localities, where seed-beds have been sterilized 

 with steam for a number of years, farmers are supplied with their own 

 boilers ; in other places one boiler is used cooperatively by several planters. 

 Road rollers, steam tractors and packing-house boilers are frequently 

 called into use for seed-bed work. In some sections the owners of steam 

 tractors or portable boilers go from place to place, sterilizing beds at fixed 

 prices. Such operators are usually supplied with all necessary equipment, 

 though sometimes they provide only the boiler and a fireman. 



"In the permanent seed-bed the pan is of such width as to fit snugly 

 within the sides of the frame, and its length varies according to require- 

 ments. A pan having an area of 72 square feet is sufficient for a 20- or 

 25-horsepower boiler, and a larger pan is difficult to move. On a bed 6 

 feet wide the pan should be 12 feet long. Where only a small boiler is 

 available, the area of the pan should be correspondingly reduced, so that 

 the boiler can maintain the desired pressure of at least 80 pounds. 



"Sterilizing pans made of galvanized iron have been extensively em- 

 ployed, but as wooden pans are cheaper and are easily made at home, wood 

 is the material now coming into general use. The wooden pan further 

 possesses the distinct advantage of reducing the loss of heat by radiation. 



"The pan is simply a shallow box (Figs. 21, 22), 4 inches being the pre- 

 ferred depth. If it is deeper, much of the desired effect is lost through the 

 more rapid cooling of the steam in the larger space exposed above the soil. 

 The frame is made of 2 by 4 inch material ; across this are laid matched 

 boards (| by 4 inches). It is advisable to put white lead in the grooves 

 to prevent the escape of steam. The boards must be securely nailed in 

 the tongue and at the sides to prevent drawing, as they swell by absorp- 



