92 VEGETABLE FORCING 
boiler pressure ranging from 50 to 70 pounds. A highly 
successful grower has found 20 pounds satisfactory when 
pans are used over loose soil. 
Preparing soil—Previous to sterilizing with either 
steam or formalin, the soil should be manured and 
plowed or spaded ready for planting. If lime is to be 
used, it also should be applied before the soil is sterilized. 
It is important for the soil to be rather open in struc- 
ture, so that the steam will penetrate every particle. It 
should also be quite moist, but not wet. More formalin 
is required in dry soil, and the results in dry soil with 
either method are unsatisfactory. The various organ- 
isms are in a live state or more active in moist soils, and 
in this condition they succumb more quickly to the 
sterilizing agents. 
Devices for sterilizing — Various devices are employed 
for sterilizing by steam. Among them may be mentioned 
boxes, pans, perforated iron pipe, perforated pipe pegs 
and ordinary drain tile. In the selection of a plan there 
are two main.considerations, viz., efficiency and economy. 
A plan may be very efficient but highly expensive, 
especially in regard to the amount of labor involved. 
There is very little specific information on the relative 
efficiency of the various plans, and it is probably not so 
much a question of plan as of thoroughness and good 
management. All of the five devices which will now be 
described have been used with success. 
Boxes.—During the earliest days of steam sterilization, 
boxes were used exclusively. They varied greatly in size, 
proportions and construction, but fundamentally they 
were similar. The general scheme was to make wooden 
boxes of convenient size, and to place perforated pipe in 
the bottom of them, The boxes were covered to confine 
the steam, and the joints were made as tight as possible. 
The pipe in the bottom of the boxes was usually 1 inch or 
1% inches in size and connected with headers 14 inch 
