Lime also makes clay less sticky. Knead up one piece of clay with rain water alone and another piece with rain water and about 1/20 its weight of lime. The limed clay breaks easily and works quite differently from the pure clay.
SUMMARY. This, then, is what we have learnt about clay. Clay is made up of very, very, tiny pieces, so small that they float in water. They stick together when they are wetted and then pressed, and they remain together; a piece of clay moulded into any pattern will keep its shape even after it is dried and baked. Clay is therefore made into bricks, earthenware, pottery, etc., whilst white clay, which is found in some places, is made into china. Wet clay shrinks and cracks as it dries; these cracks can easily be seen in the fields during dry weather. This shrinkage interferes with the foundations of houses and other buildings, causing them to settle. Dry clay is different from wet clay, it is hard, not sticky and not slippery, but it at once becomes like ordinary clay when water is added. After baking, however, clay permanently alters and cannot again be changed back to what it was before. Clay will not let water pass through; a clay field is therefore nearly always wet in winter and spring. Nor can air pass through until the clay dries or cracks.
Lime has a remarkable action on clay. It makes the little, tiny pieces stick together to form feathery flocks which sink in water; lime therefore causes muddy clay water to become clear. The flocks cannot hold water back, and hence limed clay allows water to pass through. Limed clay is also less sticky than pure clay. A clay field or garden is improved by adding lime because the soil does not remain wet so long as it did before; it is also less sticky and therefore more easily cultivated.
[1] Lime water is made by shaking up lime and water. It should be kept in a well-corked bottle.
CHAPTER IV
SOME EXPERIMENTS WITH THE SAND
Apparatus required.
Sand, about 6 lbs.; clay, about 6 lbs. Six funnels, stands and disks [1]. Six glass jars [2]. One box with glass front shown in Fig. 13 filled with clay and sand, as indicated. Quarry chalk (about 5 lbs.). Six beakers [1]. Six egg-cups [1].