hat it was before. Drying therefore alters clay only for the
time being, whilst baking changes it permanently.

[1] A little more than one-eighth of an inch.

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CHAPTER III

WHAT LIME DOES TO CLAY

Apparatus required.

_Clay, about 6 lbs. Some of the clay from Chapter II may, if
necessary, be used over again. Lime, about 1/2 lb. Six funnels,
stands and disks [2]. Twelve glass jars [2]. Lime water[1]._

If you are in a clay country in autumn or early winter you will find
some of the fields dotted with white heaps of chalk or lime, and you
will be told that these things "improve" the soil. We will make a few
experiments to find out what lime does to clay. Put some clay on to a
perforated tin disk in a funnel just as you did on p. 14, press it down
so that no water can pass through. Then sprinkle on to the clay some
powdered lime and add rain water. Soon the water begins to leak
through, though it could not do so before; the addition of the lime,
therefore, has altered the clay. If you added lime to a garden or a
field on which water lay about for a long time in winter you would
expect the water to drain away, especially if you made drains or cut
some trenches along which the water could pass. There are large areas
in England where this has been done with very great advantage.

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The muddy liquid obtained by shaking clay with water clears quickly if
a little lime is stirred in. Fill two jars A and B (Fig. 10) with rain
water, rub clay into each and stir up so as to make a muddy liquid,
then add some lime water to _B_ and stir well. Leave for a short time.
Flocks quickly appear in _B_, then sink, leaving the liquid clear, but
A remains cloudy for a long time. But why should the liquid clear? We
decided in our earlier experiments that the clay floated in the water
because it was in very tiny pieces; when we took a larger lump the clay
sank. The lime has for some reason or other, which we do not
understand, made the small clay particles stick together to form the
large flocks, and these can no longer float, but sink. If we look at
the limed clay in our funnel experiment we shall see that the same
change has gone on there; the clay has become rather loose and fluffy,
and can therefore no longer hold water back.

[Illustration: Fig. 10. Addition of lime to turbid clay water now
makes the clay settle and leaves the water quite clear]

Lime also makes clay less sticky. Knead