CH. II J Old Ideas 17 



view is incorrect. Soil is not composed of two earths: 

 it is formed of vast numbers of particles ranging without 

 any break from the largest to the smallest, and it defies 

 all attempts at being subdivided into any rigid number 

 of constituents. As a matter of convenience five or six 

 groups are distinguished, but we recognise that our 

 grouping is arbitrary. 



The material sorted out in the above experiments can 

 be used to discover some of the properties of the various 

 fractions. The coarsest material on examination is 

 found to be hard and gritty, to dry quickly and to 

 separate out readily into individual grains. The finest 

 material, on the other hand, is soft and smooth, it dries 

 slowly and forms a cake which cracks into little flakes 

 that curl up in a curious manner. If one of these flakes 

 is dropped into water it falls to the bottom in one piece, 

 but if it is rubbed between the fingers under water it 

 breaks up into particles so minute that they do not 

 settle but make the water turbid. 



The question at once arises: Why are the particles so 

 different in size ? Why are some so small and others so 

 large? An obvious answer is that the large particles are 

 perpetualh^ breaking up into little ones and that the 

 fine sand represents a sort of half-way .stage between 

 gravel and clay. This, however, is not entirely correct. 

 The sand is made of dift'erent material from the clay, 

 and we can soon see why it has not been reduced to so 

 fine a state. Put into one test-tube 1 gram of the sand 

 and into another 1 gram of the clay: add 20 c.c. of 

 strong hydrochloric acid to each, plunge the test-tubes 

 into a beaker of boiling water and leave for an hour. 

 Hydrochloric acid is a potent solvent, and dissolves 

 material that is not highly resistant. At the end of an 



R s. 2 



