ABSORBKNT P;)\\ KU OF SOILS. 1T3 



action of oil of vitriol on sugar, when placed in ten times 

 its quantity of solutions of various snlts (containing about 

 ■J- per cent of solid matter) absorbed of sulphates of soda 

 and ammonia, and clilorides of calcium and ammonium, 

 about 2 per cent ; of sulphate of potash 4 per cent ; and of 

 phosphate of soda 10 per cent. Schumacher also noticed 

 tliat sulphate of potasli is able to expel sulphate of ammo- 

 nia from lumiic acid which has been saturated with the 

 latter salt, but that the latter cannot displace the former. 

 In Schumacher's experiments, pure water freely dissolved 

 the salts absorbed by the humic acitl. 



Explanation. — Let us consider wliat occurs in the aci 

 of solution and i)i this separation of soluble matters from 

 a liquid. The difference between the solid and the liquid 

 state, so far as we can define it, lies in the unequal cohe- 

 sion of the particles. Cohesion prevails in solids, and op- 

 poses freedom of motion among the particles. In liquids, 

 cohesion is not altogether overcome but is greatly weak- 

 ened, and the particles move easily upon each other. 

 When a lump of salt i'^ put into water, the cohesion that 

 otherwise maintains its particles in the solid state is over- 

 come by the attracti(m of adhesion, which is mutually ex- 

 erted between them and the particles of water, and the 

 salt dissolves. If now into the solution of salt any in- 

 soluble solid be placed wliich the liquid can Avet (adhere 

 to) its particles will exert adhesive attraction for the par- 

 ticles of salt, and the tendency of the latter will be to 

 concentrate somewhat upon the surface of the solid. 



If the solid, thus introduced into a solution, be exceed- 

 ingly [Kjrous, or otherwise present a great amount of sur- 

 face, as in case of sand or humus, this tendency is propor- 

 tionately heightened, and a separation of the dissolved 

 substance may become plainly evident on proper examina- 

 tion. When, on the other hand, the solid surface is rela- 

 tively small, no weakening of tlie solution may be percep- 

 tible by ordinary means. Doubtless the glass of a bottle 



