COMPOSITION OF SOIL WATER 181 



vary from day to day and from soil to soil, depending on 

 daily temperature and moisture content, soil composition, 

 texture and structure, amount of organic matter, character 

 of the solvent, whether rich or poor in carbon dioxide and 

 organic acids. The figures given, however, show only wh.it 

 have been obtained bv very laborious methods from a few 

 soils, and give an idea of the amount of concentration. 



(b) Waste Water is the excess water which flows away 

 from the soil as drainage or river water. Table IX gives 

 average analyses of these two kinds of waste water. Drain- 

 age water is that which has been obtained from drains under 

 cropped fields and represents that which comes directly from 

 the soil after having passed through the soil and subsoil 

 (Fig. 38). River water is that which flows into the sea 

 and has travelled for long distances from its sources, being 

 subjected to many changes after passing through the soil. 



Table IX. — Composition of Drainage and River Waters. 



Expressed in parts per million. 



(Averages of numerous analyses except N2O5 in the case of drainage water, 

 which is from Rothamsted figures. There are not many analyses 



on this constituent.) 



Drainage. Rivers. 



Potash K2O 3.2 2.4 



Soda Na 2 15 . 1 7.1 



Lime CaO 107.6 43.2 



Magnesia MgO 16.3 14.7 



Silica Si0 2 8.5 16.4 



Carbon dioxide .... CO2 74.4 46.0 



Phosphoric acid .... P2O5 0.5 0.3 



Sulphuric acid .... SOs 60.8 8.0 



Chlorine .... .CI 17.7 3.7 



Organic matter 37.4 16.4 



Nitric acid N2O5 15.0 3.8 



Total solids 352.6 168.6 



Since the figures given for film water do not represent as 

 many types of soil as those in Table IX, comparison between 

 them is hardly feasible. Contrasting drainage water with 

 river water it is to be noted that in practically every case 

 the latter contains less of the various constituents. This is, 

 of course, to be expected, for after the drainage water has 

 entered an open stream and travelled considerable distances 



