Lessons on Soil

by Edward J. Russell

Fig. 9. A brick standing in water. The air in the brick is driven inwards by the water and forces the liquid up the tube in order to escape

One more experiment may be tried. Can a brick be changed back into clay? Grind up the brick and it forms a gritty powder. Moisten it, work it with your fingers how you please, but it still remains a gritty powder and never takes on the greasy, sticky feeling of pure clay. Indeed no one has ever succeeded in making clay out of bricks. All these experiments show that clay is completely altered when it is burnt. We also found that soil is completely altered by burning, and if you look back at your notes you will see that the changes are very much alike, so much so that we can safely put down some of the changes in the burnt soil—the red colour, the hard grittiness, and the absence of stickiness—to the clay. Let us now examine a piece of dry, but unburnt, clay. It is very hard and does not crumble, it is neither sticky nor slippery. Directly, however, we add some water it changes back to what 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.

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.

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.