CHEMISTEY OF SOILS 105 



there is no material loss of constituents of manurial value, 

 except nitrogen, in this way. 



The main facts have been known since the publication 

 of Dr. Way's 1 paper on the subject, and some of them 

 long before. For example, it is well known that water 

 from deep wells is generally purer than surface water 

 from the same locality. Way refers to Bacon's method 

 for the elimination of salt from sea water. This was, to 

 dig a hole on the seashore above high water mark, deeper 

 than the low water mark ; the water which fills the hole 

 when the tide comes in is found to be " fresh and potable." 

 Way also quotes Huxtable, who had filtered liquid manure 

 through ordinary loamy soil and found that it was deprived 

 of colour and smell ; "in fact, it went in manure and came 

 out water." 



The absorption of salts by the soil can be demonstrated 

 by filtering a solution of any potassium salt, of known 

 strength, through a long column of soil contained in a 

 tube. It will be found that the filtrate is always more 

 dilute than the original solution and that the portion re- 

 tained by the soil cannot be again completely washed out 

 with water. It is, however, only the base that is with- 

 drawn from the solution ; the acids, except phosphoric 

 and silicic acids, are not retained, but cpme through in the 

 filtrate, usually in combination with lime. Even the bases 

 are not completely absorbed ; the Amount which comes 

 through depends upon the kind of soil and varies with 

 concentration of the solution, the time of contact, and, 

 possibly, also the temperature. 



The retention of phosphoric acid is probably due simply 

 to precipitation in the form of an insoluble salt, but the 

 absorption of soluble compounds of potassium, ammonium, 

 etc., is not so easily explained. It is found that soils absorb 



1 J E. A. S E., 1850 



