CHEMISTRY OF SOILS 99 



contrary, most soils can absorb salts from solutions and 

 retain them. The drainage water which escapes from the 

 soil, however, always contains some salts in solution. The 

 amounts of these can be determined and the data are of the 

 highest importance as a means of estimating the loss of 

 plant foods in this way. The results of analysis, made by 

 Dr. Voelcker, of the drainage waters from the experi- 

 mental plots of Broadbalk (whea,t) field at Eothamsted, 

 are given on page 98. The samples were collected on Decem- 

 ber 6th, 1866 ; May 2nd, 1867 ; January 13th, April 21st, 

 and December 29th, 1868 ; and the figures given are the 

 mean of the five collections. 



Taking the mean quantities of all the constituents, it will 

 be seen that ammonia, phosphoric acid and potash are 

 present in very small quantity, and that sulphuric acid and 

 lime are by far the largest ingredients. It is curious and 

 striking that the amounts of soda and lime should be 

 respectively so much greater than those of potash and 

 magnesia. In general the acid radicles are considerably in 

 excess of the bases, but phosphoric acid and lime are con- 

 spicuous exceptions to this rule. The quantity of nitric 

 acid is less than that of any of the other acids except phos- 

 phoric, but it is nevertheless considerable. 



The variation in the Composition of the drainage from 

 the several plots may be traced largely to the influence of 

 the manures, which were applied as follows : 



Plot 2. Farmyard manure. 



3. Unmanured. 



5. Minerals only. 



6. + ammonia salts (sulphate and chloride). 



7. -f ,, (double quantity). 



8. 

 15. 



9. 

 16. 



-j- ,, (treble quantity). 



4- ,, (in autumn). 



+ nitrate of soda. 



-j- ,, ,, (double quantity). 



H 2 



