32 SOLID MATTEE 



Thus, Kinch 1 at Cirencester, during a storm from the S.W. by W. 

 (from the Bristol Channel) found as much as 44'79 parts of chlorine per 

 million of rain-water. The average quantity of chlorine found in the rain 

 at Cirencester for the fourteen years 1887 to 1900 was, during the 

 winter (September to March) periods, 3*55 parts per million, during the 

 summer (March to September) periods, 2 '2 7 parts per million. This, 

 if calculated to sodium chloride, with the average rainfalls of 14'26 in. 

 and 12 -78 in. respectively, corresponds to the deposition of 19*35 Ib. 

 common salt per acre during each winter and 10*40 Ib. during each 

 summer, or a total of 29'75 Ib. per acre per annum. In Demerara, 

 during the six years 1891 to 1895, Harrison found that the rain 

 (average fall 111 in. per annum) contained an average of 4*69 parts 

 of chlorine per million, corresponding to a total of 186 Ib. sodium 

 chloride per acre per annum. Kuston 2 at Garforth, near Leeds, 

 found an average of 3 '60 parts of chlorine per million of rain during 

 1906-1908, corresponding, if calculated to sodium chloride, to 37'3 Ib. 

 per acre per annum. 



Kain- water thus supplies a considerable quantity of solid matter, some 

 of which has manurial value, from the sea to the soil. At Valentia 

 (Ireland) Smith found about 49 parts of chlorine per million ; this 

 would correspond to about 1-5 parts of lime and 1-0 part of potash 

 per million, assuming that the chlorine was due entirely to the spray 

 of sea-water. This would mean the deposition of the equivalent of about 

 5 oz. of lime and about 3^ oz. of potash per inch of rain on each acre 

 of land. At inland places the quantities are, of course, much less, and 

 the amount of manurial mineral matter conveyed to the soil by rain is 

 usually so small as to be almost negligible. 



Water for Irrigation Purposes. In arid climates the composi- 

 tion of river water, used for irrigation purposes, is a matter of 

 considerable importance. If saline matter, especially chlorides, be 

 present, there is a danger of setting up a " brackish " or " alkali " con- 

 dition of the surface soil, which may be very destructive to plants. 

 Several of the South African rivers are distinctly alkaline from the 

 presence of sodium carbonate, and to this fact is doubtless due their 

 very muddy character and the slowness with which the suspended clay 

 separates. 



Moreover, several of the bore holes in the Transvaal yield water 

 which contains small quantities of sodium carbonate, and this fact 

 may have considerable influence when the water is used for irrigation. 



Plants show very different degrees of tolerance to the presence of 

 saline matter in the soil. As a rule sodium carbonate has the most 

 deleterious effect, followed by sodium chloride, while sodium sulphate 

 is much less harmful. In America, soils, which are " brackish " from 

 the presence of chlorides and sulphates, are known as "white alkali" 

 soils, while those containing sodium carbonate are called " black alkali " 

 soils. 



The following table (from American sources) gives the maximum 



1 Jour. Chem. Soc., Trans., 1900, 1271. 



2 Rep. No. 74, Univ. Leeds and Yorks Counc. Agric. Education, 1908. 



