up one piece of clay with rain
water alone and another piece {21} 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.

{22}

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]._

If there is a sand pit near you, or a field of sandy soil, you should
get a supply for these experiments; if not, some builder's sand can be
used. When the sand is dry you will see that the grains are large and
hard. Further, they are all separate