53 



all the steam required, and it was, moreov^er, necessary in using so 

 small a boiler in order to keep the pressure of steam high. 

 The results of these experiments are as follows : 



Bed (a) was heated to 204^ F. in 1.15 hrs. 



Bed (b) " " " " " " 45 min. 



Bed (c) " " " " " " 1. 00 hr. 



Bed (d) practically the same as (b). 

 These experiments show that bed (b) which was piped with three 

 lengths of tile gave the best results, with bed (c) following, and the 

 most unsatisfactory results were given by bed (a). Bed (d) gave 

 practically the same relative results as (b). Bed (b) contained a few 

 more feet of pipe than (c), and more than ^ more than (a), and for this 

 reason alone it might be expected that the heating of the soil in the 

 bed (b) would be more effective. There is another more important 

 difference, however, and that is in the method in which the steam 

 circulated. The cross tiles in (c) were not nearly as effective as the 

 middle lengths in (b), neither would they have been even if they had 

 contained the same linear feet. Bed (a) would have heated more 

 effectually if there had been a continuous loop. Had the four beds 

 been piped the same and all connected at once with a large boiler 

 maintaining a high pressure of steam they could have been heated 

 in two hours time. The tile which were employed for sterilizing were 

 left in the soil, but in these experiments they were not used for sub- 

 irrigation purposes. Should the soil, however, be removed and 

 replaced by other soil it would be desirable to remove the tile, which 

 can, however, be easily put back. We have tried many different 

 methods of piping with variations in the pressure of steam and we 

 will state, that in order to get the cheapest and best results it is 

 necessary to pay attention to two points, namely, that the higher the 

 pressure of steam maintained, the quicker and more effectual are the 

 results, and the greater tile area in which the steam has to circulate 

 the quicker it will find its way through the soil and accomplish the 

 sterilization of the same. It is not only necessary that there should 

 be a number of feet of pipe in the soil in order to sucessfuUy heat it,, 

 but the area of cross sections is equally important. 



In regard to the cross section area of the pipe we will relate the 



results of one of our experiments in trying to sterilize a box of soil 



with ^ in. lead pipe made up into a coil of four lengths. This coil 



had holes in it 2 in. apart and was placed in a box containing 



5 



