Top soil Subsoil Weight of dry soil before burning ... 100 100 decigrams " " " after " ... 92 97 " --- --- The part that burned away weighed ... 8 3 Weight of grit from 10 grams of dried soil 17 19 " The columns are given in Fig. 3. {8} [Illustration: Fig. 3. Columns showing what 100 parts of dried soil and subsoil were made of] Summary. The experiments made so far have taught us these facts:-- 1. Soil contains water, grit or sand, silt, clay, a part that burns away, and some white chalky specks. 2. The top layer of soil to a depth of about eight inches is different from the soil lying below, which is called the subsoil. It is less sticky, easier to dig, and darker in colour. It contains more of the material that burns away, but less clay than the subsoil. 3. When soil is dried it is not sticky but hard or crumbly; as soon as it is moistened it changes back to what it was before. But when soil is burnt it completely alters and can no longer be changed back again. [1] See p. xiv for explanation of the figures in square brackets. {9} CHAPTER II MORE ABOUT THE CLAY Apparatus required. _Clay, about 6 lbs.; a little dried, powdered clay; sand, about 6 lbs. Six glass jars or cylinders [2]. Six beakers [1]. Six egg-cups [1]. Six funnels and stands [2]. Six perforated glass or tin disks [2]. Six glass tubes [2]. Two tubulated bottles fitted with corks. Some seeds. Six small jars about 2 in. x 1 in. [2]. Bricks. The apparatus in Fig. 9. Pestle and mortar._ We have seen in the last chapter that clay will float in water and only slowly settles down. Is this because clay is lighter than water? Probably not, because a lump of clay seems very heavy. Further, if we put a small ball of clay into water it at once sinks to the bottom. Only when we rub the clay between our fingers or work it with a stick--in other words, when we break the ball into very tiny pieces--can we get it to float again. We therefore conclude that the clay floated in our jars (p. 6) for so long not because it was lighter than water, but because the pieces were so small. Clay is exceedingly useful because of its stickiness. Dig up some clay, if there is any in your garden, or procure some from a brick works. You can mould it into any shape you like, and the purer the clay the {10} better it acts. Enormous quantities of clay are used for making bricks. Make some model bricks about an inch long and half an inch in width and depth, also make a small basin of about the same size, then set them aside for a week in a warm, dry place. They still keep their shape; even if a crack has appeared the pieces stick together and do not crumble to a powder.