STEAM STERILIZATION OF SEED BEDS. 9 



which are laid over them on the outside, at right angles to them, 

 extending the length of the box, and which are very securely nailed 

 at the ends (fig. 1). The cover boards are then nailed from the 

 inside to the outside planks, the object being to prevent the swelling 

 and warping of the cover boards. A good view of the inside con- 

 struction of the box is shown in figure '2. 



Two ring bolts are set in each side of the frame on the top, one 

 near each corner. Through the rings ax handles or bars are thrust 

 to serve as handles in moving the pan along the bed, as shown in 

 the title-page illustration. 



A strip of J-inch felt packing, 2 inches wide, is placed along 

 the lower edge of the frame, on the outside, to prevent the escape 

 of the steam. The hoop iron is then laid on the packing and 



PI609T 



Fi<:. 2. The under side of a wooden sterilizing pan made of 2 by 4 inch frame and g-inch 

 matched cover boards. Hoop iron laid over thin felt and lapped over the edge sur- 

 rounds the outside of the frame, forming a knife-edge joint in the soil to prevent the 

 loss of steam. A i-inch nipple is inserted in one end, through which the steam enters. 



nailed every 4 inches, one-half its width extending beyond the lower 

 edge of the frame, as shown in figures 2 and 3. When the packing 

 can not be had, the iron is nailed to the inside of the frame instead 

 of the outside. Instead of the hoop iron, 2-inch angle iron is some- 

 times used. This is fastened to the lower side of the frame, to form 

 a tight joint when the box is laid on the soil. A piece of thin pack- 

 ing serves to prevent the escape of steam between the iron and the 

 bottom of the wooden frame to which it is nailed. Angle iron, be- 

 cause of its heavier character, will not bend and is better than hoop 

 iron, but it requires careful working to fit it to the frame. 



In the middle of one end of the frame is set a f -inch pipe-threaded 

 nipple, 6 or 7 inches in length, through which the steam is delivered 

 into the pan. The nipple should project 3 inches from the box, to 



