94 



It docs not appear that the apparent absence of the chlorine 

 can be explained by a failure of the method. A more probable 

 hypothesis is that the absorption of the chlorine by the soil took 

 place to the extent of trio amount present in the solution used. 

 If these soils contained 3, 5 or 7 parts per million more chlor- 

 ine than could be recovered by the method of washing used, it is 

 quite probable thai; when a solution, carrying these amounts 

 of chlorine, is allowed to sweep the soil by capillary action, it 

 may be able to displace a portion of that already present, and 

 to such an extent that that which the solution carries would be 

 absorbed sufficiently during the 20 days so that the amounts 

 which could then be recovered by washing are too small to be 

 measured by the methods used. 



This view finds support in the retention of nitrates by soils 

 in forms still recoverable by suitable treatment. 



RECOVERY OF ABSORBED NITRIC ACID. 



During the investigations relative to the movements of ni- 

 trates in soils under furrow irrigation, reported in Bulletin 

 No. 119, Office of Experiment Stations, a series of observations 

 was made which demonstrated that nitrates absorbed by soils 

 may be displaced by capillary sweeping with distilled water. 



When an effort was made to account for the increase of ni- 

 trates under the rows, referred to in the observations previously 

 cited, p. 69, it was found that there was not enough nitric acid 

 in the water added by irrigation plus that which appeared to 

 have been lost from the soil beneath the furrows to account for 

 the gain which had occurred beneath the rows. Moreover, the 

 very short intervals of time during which the observed gains 

 had taken place, togelher with the great depth below the sur- 

 face where the increases were observed, appeared, at that time, 

 to preclude the possibility that such additions to the soil could 

 be made through nitrification; and it appeared that in some 

 manner the capillary sweeping had the effect of washing the 

 soil grains more thoroughly than was done by the method used 

 in the laboratory and that, on this account, there resulted a con- 



