SOIL STERILIZATION 93 
larger. They were placed 12 to 15 inches apart and 
closed at the ends opposite the headers. The holes in the 
pipe were usually 4% or % inch in diameter, about a foot 
apart, and turned down to prevent them from being 
stopped with dirt. It is probable that the boxes should 
never be more than a foot deep. Two-inch drain tile may 
be substituted for iron pipe. With an ample volume of 
steam under high pressure thorough sterilization can be 
effected in an hour. The boxes may be covered with 
heavy canvas or hotbed sash. When a large amount of 
soil is to be sterilized there should be at least two boxes 
to facilitate handling the soil. While the box method is 
convenient for sterilizing potting soils, flats, tools, etc., it 
is now seldom used in vegetable-growing establishments 
because of the excessive cost of handling the soil. 
Pans.—The inverted pan method is used by a great 
many large growers, especially in the Cleveland district. 
It is regarded by some as not so thorough as the tile and 
perforated pipe plans, although some of the most careful 
and successful growers are unwilling to concede this 
point. There are examples of perfect pan sterilization of 
soils which had become most seriously infested with 
nematodes and many other destructive pests. The pan 
method does not require any handling of the soil, and 
this is unquestionably its greatest advantage. The plan 
is becoming more popular every year. It is particularly 
valuable for open, porous soils which are easily pene- 
trated by steam. 
Galvanized iron pans are the most durable. They may 
be of any convenient size. Fig. 29 shows a pan which is 
used at Purdue University. Sometimes they are only 
4 feet wide and 8 to 12 feet long. The pans are usually 
6 to 8 inches deep. Pipe connection is made at the side 
or end as shown in the illustration, or in the bottom of 
the middle of the sterilizer with an ell and a nipple on the 
outside for the attachment of a hose of inch size or larger. 
