[Illustration: Fig. 2. Columns showing what 100 parts of soil and subsoil were made of] The dried lumps of soil are now to be broken up finely with a piece of wood, but nothing must be lost. It is easy to see shrivelled pieces of plant, but not easy to pick them out; the simplest plan is to burn them away. The soil must be carefully tipped on to a tin lid, or into a crucible, heated over a flame and stirred {5} with a long clean nail. First of all it chars, then there is a little sparkling, but not much, finally the soil turns red and does not change any further no matter how much it is heated. The shade of red will at once be recognised as brick red or terra cotta, indeed "terra cotta" means "baked earth." When the soil is cold it should be examined again; it has become very hard and the plant remains have either disappeared or have changed to ash and crumble away directly they are touched. On weighing a further loss is discovered, which was in our experiment:-- Weight of top soil after drying but before burning ... 83 decigrams " " " " " " after " ... 76 " -- The part that burnt away weighed ... 7 " Weight of subsoil after drying but before burning ... 87 decigrams " " " " " after " ... 84 " -- The part that burnt away weighed ... 3 " These results are entered on the column in Fig. 2. The surface soil is seen to contain more material that will burn away than the subsoil does. When the burnt soil is moistened it does not become dark and sticky like it did before, it has completely changed and cannot be made into soil again. It is more like brick dust than soil. For further experiments we shall want a fresh portion of the original soil. On a wet afternoon something was noticed that enabled us to get a little further with our studies. The rain water ran down a sloping piece of ground in a tiny channel it had made; the streamlet was very muddy, and at first it was thought that all the soil was washed away. But we soon saw that the channel was lined {6} with grit, some of which was moving slowly down and some not at all. Grit can therefore be separated from the rest of the soil by water.