SOLID MATTER. 37 



In air are to be found dust particles of every description, 

 blown up from the surface of the ground and consisting of 

 fragments of very diverse character. 



In addition, air, even at considerable heights, contains solid 

 particles of a more definite and uniform character the minute 

 particles left by the evaporation of the tiny droplets of the 

 spray from the sea. Each drop of the spray loses its water 

 by evaporation and leaves an excessively minute particle of 

 dust, which remains suspended in the air until washed out 

 by rain. These saline particles are naturally most abundant 

 near the coast, as is evident from the analyses of rain-water ; 

 but at places far inland, chlorine is to be found in rain-water, 

 and sometimes in considerable quantities. 



Rain-water thus supplies a considerable quantity of solid 

 matter from the sea to the soil. At Valencia (Ireland) Smith 

 found about 49pts. of chlorine per million ; this would corre- 

 spond to about l'5pts. of lime and 1/Opt. 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 ounces of lime and about 3^ ounces of potash per 

 inch of rain on each acre of land. At inland places the quan- 

 tities are, of course, much less, and the amount of saline 

 matter conveyed to the soil by rain is usually so small as to be 

 almost negligible. 



