Read Ebook: Roundabout to Moscow: An Epicurean Journey by Bouton John Bell

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CHAP. PAGE

FIGURE PAGE

The photographs of the pot experiments are by Mr Lionel Armstrong.

INTRODUCTION

It is not desirable to work through a chapter in one lesson. Children unaccustomed to make experiments or to see experiments done, will probably require three or four lessons for getting through each of the first few chapters, and two or three lessons for each of the others.

A supply of sand, of clay, and of lime will be wanted, but it is not necessary to have fresh material for each lesson. The sand may be obtained from a builder, a sand pit, the sea shore or from a dealer in chemical apparatus. The clay may be obtained from a brick yard; it gives most satisfactory results after it has been ground ready for brick making. Modelling clay is equally satisfactory. A supply of rain water is desirable.

For a class of twelve children working in pairs at the experiments the following apparatus is wanted for the whole course:--

Six tripods and bunsen burners or spirit lamps twelve pipe-clay triangles twelve crucibles or tin lids sixteen gas jars twelve beakers 250 c.c. capacity two beakers 500 c.c. two beakers 100 c.c. six egg-cups twelve funnels six funnel stands six perforated glass disks two tubulated bottles 500 c.c., four corks to fit cork borers 4 lbs. assorted glass tubing pestle and mortar twelve Erlenmeyer flasks 50 c.c. six saucers twelve flatbottomed flasks 100 c.c., six fitted with India rubber stoppers bored with one hole , and six with ordinary corks box as in Fig. 13 six glass tubes 1/2" diameter, 18" long six lamp chimneys six test tubes, corks to fit three thermometers soil sampler balance and weights two retort stands with rings and clamp.

The figures given in square brackets are the quantities that suffice when the teacher alone does the experiments, it not being convenient for the scholars to do much.

In conclusion the author desires to tender his best thanks to the Rev. Cecil Grant of St George's School, and to Mr W. J. Ashby of the Wye School, for having allowed him the use of their schools and appliances during the progress of these lessons. Especially are his thanks due to Mr Lionel Armstrong for much help ungrudgingly rendered in collecting material, taking photographs, and supervising the experiments.

E. J. R.

HARPENDEN, February, 1911.

WHAT IS THE SOIL MADE OF?

Apparatus required.

If we talk to a farmer or a gardener about soils he will say that there are several kinds of soil; clay soils, gravel soils, peat soils, chalk soils, and so on, and we may discover this for ourselves if we make some rambles in the country and take careful notice of the ground about us, particularly if we can leave the road and walk on the footpaths across the fields. When we find the ground very hard in dry weather and very sticky in wet weather we may be sure we are on a clay soil, and may expect to find brick yards or tile works somewhere near, where the clay is used. If the soil is loose, drying quickly after rain, and if it can be scattered about by the hand like sand on the sea shore, we know we are on a sandy soil and can look for pits where builder's sand is dug. But it may very likely happen that the soil is something in between, and that neither sand pits nor clay pits can be found; if we ask what sort of soil this is we are told it is a loam. A gravel soil will be known at once by its gravel pits, and a chalk soil by the white chalk quarries and old lime kilns, while a peat soil is black, sometimes marshy and nearly always spongey to tread on.

We want to learn something of the soil round about us, and we will begin by digging a hole about three feet deep to see what we can discover. At Harpenden this is what the scholars saw:--the top eight inches of soil was dark in colour and easy to dig; the soil below was reddish brown in colour and very hard to dig; one changed into the other so quickly that it was easy to see where the top soil ended and the bottom soil began; no further change could, however, be seen below the eight inch line. A drawing was made to show these things, and is given in Fig. 1. You may find something quite different: sand, chalk, or solid rock may occur below the soil, but you should enter whatever you see into your notebooks and make a drawing, like Fig. 1, to be kept for future use. Before filling in the hole some of the dark coloured top soil, and some of the lighter coloured soil lying below , should be taken for further examination; the two samples should be kept separate and not mixed.

First look carefully at the top soil and rub some of it between your fingers. We found that our sample was wet and therefore contained water; it was very sticky like clay and therefore contained clay; there were a few stones and some grit present and also some tiny pieces of dead plants--roots, stems or leaves, but some so decayed that we could not quite tell what they were. A few pieces of a soft white stone were found that marked on the blackboard like chalk. Lastly, there were a few fragments of coal and cinders, but as these were not a real part of the soil we supposed they had got in by accident. The subsoil was also wet and even more sticky than the top soil, it contained stones and grit, but seemed almost free from plant remains and from the white chalky fragments.

A few experiments will show how much of some of these things are present. The amount of water may be discovered by weighing out ten grams of soil, leaving it to dry in a warm place near the fire or in the sun, and then weighing it again. In one experiment the results were:--

A column 100 millimetres long was drawn to represent the 100 decigrams of soil, and a mark was drawn 17 millimetres up to show the amount of water .

Another column should be drawn for the subsoil. On drying the soil it becomes lighter in colour and loses its stickiness, but it has not permanently changed because as soon as water is added it comes back to what it was before.

The dried lumps of soil are now to be broken up finely with a piece of wood, but nothing must be lost. It is easy to see shrivelled pieces of plant, but not easy to pick them out; the simplest plan is to burn them away. The soil must be carefully tipped on to a tin lid, or into a crucible, heated over a flame and stirred with a long clean nail. First of all it chars, then there is a little sparkling, but not much, finally the soil turns red and does not change any further no matter how much it is heated. The shade of red will at once be recognised as brick red or terra cotta, indeed "terra cotta" means "baked earth." When the soil is cold it should be examined again; it has become very hard and the plant remains have either disappeared or have changed to ash and crumble away directly they are touched. On weighing a further loss is discovered, which was in our experiment:--

Weight of top soil after drying but before burning ... 83 decigrams " " " " " " after " ... 76 " -- The part that burnt away weighed ... 7 "

Weight of subsoil after drying but before burning ... 87 decigrams " " " " " after " ... 84 " -- The part that burnt away weighed ... 3 "

These results are entered on the column in Fig. 2.

The surface soil is seen to contain more material that will burn away than the subsoil does. When the burnt soil is moistened it does not become dark and sticky like it did before, it has completely changed and cannot be made into soil again. It is more like brick dust than soil.

For further experiments we shall want a fresh portion of the original soil.

On a wet afternoon something was noticed that enabled us to get a little further with our studies. The rain water ran down a sloping piece of ground in a tiny channel it had made; the streamlet was very muddy, and at first it was thought that all the soil was washed away. But we soon saw that the channel was lined with grit, some of which was moving slowly down and some not at all. Grit can therefore be separated from the rest of the soil by water.

This separation can be shown very well by the following experiment. Rub ten grains of finely powdered soil with a little water , and carefully pour the muddy liquid into a large glass jar. Add more water to the rest of the soil, shake, and again pour the liquid into the jar; go on doing this till the jar is full. Then get some more jars and still keep on till the liquid is no longer muddy but nearly clear. The part of the soil that remains behind and will not float over into the jars is at once seen to be made up of small stones, grit, and sand. Set the jars aside and look at them after a day or so. The liquid remains muddy for some time, but then it clears and a thick black sediment gathers at the bottom. If now you very carefully pour the liquid off you can collect the sediments: they are soft and sticky, and can be moulded into patterns like clay. In order to see if they really contain clay we must do the experiment again, but use pure clay from a brick yard, or modelling clay, instead of soil. The muddy liquid is obtained as before, it takes a long time to settle, but in the end it gives a sediment so much like that from the soil, except in colour, that we shall be safe in saying that the sediments in the jars contain the clay from the soil. And thus we have been able to separate the sticky part of the soil--the clay--from the gritty or sandy part which is not at all sticky. We may even be able to find out something more. If we leave the soil sediment and the clay sediment on separate tin lids to dry, and then examine them carefully we may find that the soil sediment is really a little more gritty than the clay. Although it contains the clay it also contains something else.

When the experiment is made very carefully in a proper way this material can be separated from the pure clay. It is called silt, but really there are a number of silts, some almost like clay and some almost like sand; they shade one into the other.

If there is enough grit it should be weighed: we obtained 14 decigrams of grit from 10 grams of our top soil and 17 decigrams from 10 grams of bottom soil. We cannot separate the clay from the silt, but when this is done in careful experiments it is found that the subsoil contains more clay than the top soil. We should of course expect this because we have found that the subsoil is more sticky than the top soil. These results are put into the columns as before so that we can now see at once how much of our soil is water, how much can burn away, how much is grit, and how much is clay and other things.

The columns are given in Fig. 3.

Summary. The experiments made so far have taught us these facts:--

See p. xiv for explanation of the figures in square brackets.

MORE ABOUT THE CLAY

Apparatus required.

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 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 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.

Another thing that you will have noticed is that anything made of clay holds water. A simple way of testing this is to put a round piece of tin perforated with holes into a funnel, press some clay on to it and on to the sides of the funnel , and then pour on rain water. The water does not run through. Pools of water may lie like this on a clay field for a very long time in winter before they disappear, as you will know very well if you live in a clay country. So when a lake or a reservoir is being made it sometimes happens that the sides are lined with clay to keep the water in.

If water cannot get through can air? This is very easily discovered: plug a glass tube with clay and see if you can draw or blow air through. You cannot. Clay can be used like putty to stop up holes or cracks, and so long as it keeps moist it will neither let air nor water through. Take two bottles like those in Fig. 8, stop up the bottom tubes, and fill with water. Then put a funnel through each cork and fit the cork in tightly, covering with clay if there is any sign of a leak. Put a perforated tin disk into each funnel, cover one well with clay and the other with sand. Open the bottom tubes. No water runs out from the first bottle because no air can leak in through the clay, but it runs out very quickly from the second because the sand lets air through. These properties of clay and sand are very important for plants. Sow some seeds in a little jar full of clay kept moist to prevent it cracking, and at the same time sow a few in some moist sand. The seeds soon germinate in the sand but not in the clay. It is known that seeds will not germinate unless they have air and water and are warm enough. They had water in both jars, and they were in both cases warm, but they got no air through the clay and therefore could not sprout. Pure clay would not be good for plants to grow in. Air came through the sand, however, and gave the seeds all they wanted for germination.

This also explains something else that you may have noticed. If you tried baking one of your model bricks in the fire you probably found that the brick exploded and shattered to pieces: the water still left in the brick changed to steam when it was heated, but the steam could not escape through the clay, and so it burst the clay. In a brick works the heat is very gradually applied and the steam only slowly forms, so that it has time to leak away, then when it has all gone the brick can be heated strongly. You should try this with one of your model bricks; leave it in a hot place near the stove or on the radiator for a week or more and then see if you can bake it without mishap.

Let us now compare a piece of clay with a brick. The differences are so great that you would hardly think the brick could have been made from clay. The brick is neither soft nor sticky, and it has not the smooth surface of a piece of clay, but is full of little holes or pores, which look as if they were formed in letting the steam out. A brick lets air through; some air gets into our houses through the bricks even when the windows are shut. Water will get through bricks more easily than it does through clay. After heavy rain you can often find that water has soaked through a brick wall and made the wall paper quite damp. A pretty experiment can be made with the piece of apparatus shown in Fig. 9: bore in a brick a hole about an inch deep and a quarter of an inch wide, put into the hole the piece of bent glass tubing, and fix it in with some clay or putty, then pour some water blackened with ink into the tube, marking its position with a label. Stand the brick in a vessel so full of water that the brick is entirely covered. Water soaks into the brick and presses the air out: the air tries to escape through the tube and forces up the black liquid.

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.

A little more than one-eighth of an inch.

WHAT LIME DOES TO CLAY

Apparatus required.

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.

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.

Lime water is made by shaking up lime and water. It should be kept in a well-corked bottle.

SOME EXPERIMENTS WITH THE SAND

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