THE STERILISATION OF SOIL 385 



at intervals running along the bottom, and after putting the 

 soil to be treated into it and covering over with a canvas 

 cloth, we may drive steam from a boiler through it. If this 

 method be adopted (as is done in several commercial growers' 

 places now), pressure of 60 Ib. to 80 Ib. to the square inch is 

 required. A modification of this method is in use in green- 

 houses, where a movable frame of perforated pipes is laid so 

 as to cover half a bed, and soil from the other half is thrown 

 over it and covered with canvas. The steam is then driven 

 through and the temperature raised to the required degree. 

 The frame can then be moved on, and so the whole house 

 may be treated a piece at a time. 



Baking the Soil. Where steam-heat cannot be obtained, 

 baking the soil may be resorted to ; but this should not be 

 done to such an extent that the soil becomes charred. Several 

 methods besides the use of the kitchen oven are in vogue. 

 Heating the soil on a shovel over a fire, thrusting red-hot iron 

 plates or even hot bricks into the soil heap, may be practised. 

 Treatment by Chemicals. Carbolic acid, formalin, naphtha- 

 lene, carbon bisulphide and so on are used at times ; but their 

 use is not unattended by danger to the crops to follow, and is 

 not always satisfactory. The only method which at present 

 seems to offer some degree of success outside is the use of 

 powdered quicklime, dug in while still in a thoroughly caustic 

 state. Potash salts also apparently have a slightly sterilising 

 effect, especially kainit. No doubt in time some substance 

 injurious to animals such as the eelworms and minute creatures 

 which prey on bacteria, will be found sufficiently cheap to act 

 as a soil steriliser, and with it will begin a new era for those 

 whose business it is to gather the riches of the soil. 



2 B 



