BIOLOGY OF THE SOIL. 77 



On the other hand, American investigators found as much 

 as from O43 to 44-0 parts of potash (K 2 O) in a million of 

 drainage water.* 



Way found from 0*3 to 3'1 parts K 2 O and up to 1-7 parts 

 P 2 O r , per million of drainage water, f 



Schloesingl states that the amount of phosphoric acid in the 

 water impregnating soils is usually about 1 mgm. per litre, but 

 sometimes is as much as 2 or 3 mgms. 



The composition of drainage water naturally varies with 

 many circumstances, e.g., rainfall, &c. Complete analyses 

 have not recently been published. The average of analyses 

 by Way (1856), Krocker (1853), and Zoller (1857) gave the 

 following : 



Parts per million. 



Potash, K,0 ... ... 2 to 60 



Phosphoric acid, P 2 5 ... traces to 2 



Lime, CaO ... ... 68 to 180 



Soda, Na 2 ... ... 5 to 46 



Silica, SiO. 2 ... ... 5 to 25 



Sulphuric acid, S0 3 ... 18 to 130 



Organic matter ... ... 16 to 180 



Nitric acid, N 2 5 ... 2 to 210 



Ferric oxide and alumina... 0*7 to 7 



Chlorine 1 to 57 



Total solids (average) ... 365 



Biology of the Soil. Micro-organisms of various kinds 

 have been found in air, water, soil, and almost all natural 

 media. The soil, being the scene of such numerous processes 

 of decay, oxidation, and chemical change, is found to be teem- 

 ing with myriads of minute forms of life, each engaged 

 in carrying on the chemical changes essential to its growth, 

 whenever the conditions are favourable. For specific infor- 

 mation with reference to the history of micro-organisms and 



* Massachusetts State Station Report 1883, p. 27. t J.R.A.S. 1856, 133. 



J Compt. Rend. 127, 236; J.C.S. 1S99 abst, ii., 119. 



Various estimates of the number of micro-organisms present in 1 gramme of soil 

 (obviously the number will greatly vary) have been made, some authorities estimating 

 them at from 750 000 to 1,000,000, while in a black peaty soil from Russia 60,000,000 

 were thought to be present. 



