1902.] PUBLIC DOCUMENT — No. 33. 81 



inserted at intervals which readily fit into the extension 

 pipes (see Figs. 1 and 2). In some instances the headers 

 are placed at each end, thus forming with the extension 

 pipes a frame composed of a series of rectangles (Fig. 2). 

 In this form a complete circulation of the steam can take 

 place. In others the headers are in the middle, and the 

 extension pipes lead off in opposite directions (Fig. 1). 

 In the latter case the ends of the extension pipe are plugged 

 with wood, and a complete circulation of steam does not 

 occur. The material most frequently used is iron pipe. 

 The form devised by Mr. Cartter is constructed out of 

 perforated galvanized-iron tubes, and is very light and easy 

 to handle. 



The method generally adopted by' lettuce growers in heat- 

 ing their soils is to place the apparatus on the surface of 

 the bed. If the bed is 20 feet wide, then it will be most 

 convenient to have the heating appliance about 10 feet wide 

 and 20 to 30 feet long. This is placed midway between the 

 edges of the bed, and the soil to the depth of 1 foot is dug 

 out on either side of the appliance and thrown on top of it. 





-a 



Fig. 3. — Plan of house, showing methods of sterilization : b, c, successive positions of the 



apparatus. 



This covers the heating apparatus to a depth of 1 foot. The 

 steam is now turned on and the soil heated. After sufficient 

 steaming has taken place, the pipes can be pulled out and 

 set up ready for the next treatment (see Fig. 3). The soil 

 previously treated should be covered up with some old 

 canvas, if available, or, in fact, with anything that will 

 retain the heat, and allowed to stand some hours, after 

 which the top portion is shovelled back to where it was 

 taken from. Not only is the 1 foot of top soil heated by 



