52 SOIL STERILIZATION 



turned out, covered up well to keep the heat in as long 

 as possible, and then the box should be refilled. Such is 

 the simple process now often used. Its cost depends 

 upon individual methods, and varies from 20c. to 50c. a 

 load. 



Other means than sterilization by steam are rotation 

 of crops and the use of various disinfectants. Dr. E. J. 

 Russell, director of the Rothamsted Experimental Sta- 

 tion in England, has recently done much work in this 

 direction, and has published the results, f These, together 

 with the discoveries along the same line by other investiga- 

 tors, have been summed up in various papers. Russell 

 divides the disinfectants proper into three classes, according 

 to their efficiency. In the first class are the strongest, as 

 formaldehyde, pyridine, Iutidin and colidin. The second 

 class includes benzol, calcium sulphide, carbolic acid, 

 cresilic acid, Jight and heavy solvent naphtha, petroleum 

 and toluol. The third and weakest class contains only 

 naphthalin and its derivatives. 



The first consideration in applying these disinfectants 

 is whether there are plants on the land to be treated. If 

 there are, and they cannot be removed, only the weaker 

 means can be used which do not injure the roots. The 

 steam treatment is generally too expensive, also formalde- 

 hyde, the pyridine bases, benzol and tuluol. Benzol, 

 benzine, petroleum and toluol are also dangerous because 

 of fire. The other representatives of the second group are 

 said to be far better. 



The so-called California solution, which contains a 

 calciumoxy-sulphide, is largely used against animal and 

 vegetable pests, especially by fruit and Rose growers. 

 An important disinfectant is cresilic acid, with its deriva- 

 tives, creolin, lysol and carbolineum, which are obtained 



