82 HATCH EXPERIMENT STATION. [Jan. 



this method, but the soil under which the apparatus rests is 

 equally well done, provided too much haste is not made in 

 removing the treated soil. In one case that was examined, 

 where the steam was left on for one and one-half hours late 

 in the afternoon, and the top coat of soil not disturbed until 

 the next morning, we obtained the following records of soil 

 temperatures at noon on the following day, or nineteen hours 

 after the steam was applied and five hours after the top soil 

 and apparatus had been removed : temperature of soil 2 feet 

 below the surface, 120° F. ; temperature of soil 1 foot below 

 the surface, 175° F, Two masses of top soil were heated 

 in this instance during the one and one-half hours, the last 

 one being left on over night. The average pressure of 

 steam applied was only 13 pounds. It always astonishes 

 those who heat soil for the first time to find that steam can 

 penetrate such a distance below the surface in so brief a 

 period. In this particular case the steam was oozing out 

 of the soil 30 inches below the surface, no examination below 

 this depth being made. The most eflicient appliances for 

 sterilization are those based upon our recommendations in 

 former publications. A 2 inch pipe is superior to a 1 inch, 

 1^4 inch or 1% inch pipe. A high pressure of steam is 

 more effectual than a low pressure, and the larger the num- 

 ber of perforations in the pipe, the more widely and evenly 

 is the steam disseminated and the more quickly and cheaply 

 can the soil be heated . The area of a series of small holes 

 placed uniformly in a given length of pipe would undoubtedly 

 be more effectual than the same area of larger holes in the 

 same length of pipe. In the latter case the holes would be 

 further apart, and allow larger volumes of steam to escape ; 

 in the former case they would be nearer together, and would 

 be capable of heating the soil more evenly and in our opinion 

 more effectually. In our judgment, holes % inch in diam- 

 eter, when placed near together, would be sufficient for the 

 exit of steam, and the soil would be less likely to go through 

 them than through holes 14 iiich in diameter. 



In proportion as the appliances have been improved for 

 sterilizing soils, the cost of the operation has been greatly 

 reduced. From reliable estimates which we have been able 



