COMBUSTION
Combustion
HOW SHOULD CHEMISTRY be introduced to children? The child is at first much more at home with the concepts of physics, for the action of light and sound in nature is much more obvious. The simplest way of showing the essential elements of chemical action is through the phenomenon of combustion. In it lies hidden the entire chemical process. It is the best point of departure.
The combustion of quite a series of substances should be demonstrated. Let us suppose it is an autumn day. From a walk in the woods the children bring back all manner of combustible substances; dry leaves, twigs, bark, dry moss, dead grass, pine cones, and so on. To these are added various kinds of wood, green vegetable matter, straw, cottonwool, paper, wax, olive oil and petroleum. We show how each of these parts of the plant and other substances burn. When ignited varying appearances of the flame result. It is often possible to recognise exactly the nature of the plant from the form of the flame. Thus, grasses burn with a pointed flame; pine needles flare and sputter; cones burn intensely and with a noisy crackling, each type of leaf differently. A complete ” Botany of Flame ” results. The children notice that the whole inner nature of the plant flares up once again in the flame. The other substances produce quite a different sort of flame.
Attention may now be drawn to this. On the one side light and heat are always produced. They appear as flame. On the other side the ash remains. The ash is mineral, dead. The children should be taught the phenomenon of this opposition of light and heat against ash and assimilate it thoroughly. Children with a touch of the melancholy in their temperament are attentive to the fact that of this beauty only ash remains. Choleric children are particularly affected by the flame. For all children the flame represents something essentially living.
It is necessary to be cognisant not only with what goes on in the child mind during the day, but also with what it experiences in the night. What the child has observed recurs next day at the commencement of the lesson as an unconscious query as to the true nature of the matter.
There should be little difficulty in eliciting these and similar thoughts from the children through judicious questions, or they may even volunteer them of their own accord. One might ask: whence does light come ? It is nothing other than the sunlight which the plants have absorbed. The sun shines down upon the earth, the plant shoots up and in its turn grows towards the sun. All living things can be burned. When you ignite a fire the light returns to the sun.
What happens in combustion can now be felt by the children. What had been completely materialised as wood or coal, becomes invisible and disappears. The light is released.
The children thus grasp a very important opposition. That of light and weight. They are already accustomed to regarding things in terms of opposites of this kind.
One can now speak of the living plant. Just look at their flowers! Often they seem like flames with their gay red or yellow blossoms. Think for instance of the red poppy! And does much ash remain when these are burned ? No. But if you were to burn the roots there would be a lot of ash. Roots do not shine so bravely. Why ? Flowers are in themselves a form of burning, not in their roots, but in the fact of blossoming. They are akin to heaven, their beauty reveals it. But the roots belong to the earth. That is why they leave so much dead mineral matter, so much ash. What are plants really ? They are living flames! From their green heart the flower escapes heavenward like a flame. But the ash sinks downwards into the root.
Once the children have mastered these elements one can summarise the whole thing in a coloured diagram on the blackboard. Such a picture remains significant throughout life. In this way one may avoid the temptation to regard the phenomenon of combustion as a purely material chemical process. One relates it with the whole world. The burning process later to be completed with the dead parts of the plant can be seen going forward while it still lives. What plants do in the process of growing, blossoming and striking root, is simply continued in a more violent and destructive way when they are burned. That which takes place in a modified way within the rhythm of life, in the flower and the root, is torn asunder when they burn, into shining flame and ash.
This can now be linked up with man. Does burning take place in man ? The children can easily see how warmth has its part in the blood, in the digestive process and in the activity of the limbs. They can feel how warmth acts from within themselves and know that the internal organs are the warmer. But what part of man contains the greatest quantity of ash ? The bone. A sort of flame burns in man, but it is the reverse of the process found in plants.
An approach of this kind can be further developed. The class is reminded of what fire—as used in the funeral pyre—for instance—has meant to man, even in the remotest ages. Just as in burning, the light escapes from matter, so does the soul from the living body of man, leaving behind the corpse. This gives an opportunity of introducing historical and religious ideas. The soul dwells in the living body as light dwells in inflammable matter. Thus by the intimate association of the scientific with the artistic, the sphere of religion and the spirit can be approached. The significance of fire in sacrifice can here be called to mind as well as the connection with heaven which man seeks to build through the sacrificial flame.
Such a point of view can be summarised in simple sentences and dictated to the children. With great interest they have painted the various flames in their experiments and have also had depicted to them the action of fire in plant and man.
“Everything living is inflammable. Thus if we set fire to the dried parts of plants, flames break forth. Light and heat fly upward into the wide world. But the ash is left behind. The light is bright and without weight. The ash is heavy and must fall to earth. Thus every burning is a separation of light from the heaviness of earth. In burning a light that has been bewitched into the plant, makes its escape. It is the power of the sunlight which it has taken into itself. It is just the same when we burn anything from the body of an animal; for the hidden light enters into the animal body, as also into the human, through the plants that are consumed as food. The plant is a living flame. It burns upwards to the blossom. In man and in animals there are living flames, but they burn in a different direction. When we look at fire we feel how it consumes everything and bears it back once more to heaven from whence all things come down to the earth.
” ‘ And what the might of fire doth seize, No longer monstrous, cumbering earth; Is whirled away and vanishing, Hastes up to where it had its birth.’ ”
Flame requires air that it may live. A current of air makes it stronger, it gets weaker when there is less air. The rate of burning and the intensity of the heat depend on the amount of air which reaches the flame. A lighted candle will soon go out if you place it under an inverted glass jar. At this stage a well-known experiment can be carried out, in which a bell jar is inverted over a lighted candle floating on a cork on the surface of a dish of water. After a while the candle goes out and the surface of the water on which the candle floats rises within the jar by about one-fifth of its height. The child sees that the flame has consumed some of the air. At this stage there is no need to speak of oxygen. The realisation that the air excites the flame and in its turn is partly consumed, will suffice. A series of flames in which air is introduced in increasing quantities is now shown. One might show a candle flame, then blow into it with a blow pipe and follow with a demonstration of the Bunsen-burner and finally demonstrate forge and bellows. This intensification shows the children the action of air on flame and also how increasing effort is needed to supply the flame with air, until finally in the forge the bellows must be worked with the foot. At the same time the children are being familiarised with a number of contrivances they will later find in general use. Attention is drawn to the fact that without added air the flame is a clear yellow and not too intense; comparatively cool, but the introduction of air changes it to a blue hot flame. A candle flame is shown. Why is it blue nearest the wick ? Because there is gas inflammable until it reaches the periphery. The children’s interest is roused when they first observe that the intense blue space of the forge becomes invisible when viewed against a light background—as for instance when the sun shines on the wall behind it.
Before proceeding to more abstract chemistry, the child must first have the experience of the Fire Element. In this way the nature of flame is linked up with the whole universe and with man. One may now proceed to the practical use of flame, for instance in lighting and in heating.
One starts with the phenomenon of the luminous flame which deposits soot on a cold surface. Carbon therefore has its origin in the flame. This carbon shines, but only when there is not too much air. When this happens it is burnt and gives out heat. This can be illustrated by the bright flame of acetylene which deposits a heavy soot, and the hot blue non-luminous gas flame. With the one you may illuminate, with the other heat— for example a gas oven. Flame always plays to and fro between light and air. It is warmth which forms the link between the two opposites of light and air. A question might then be put: Would it not be possible to illuminate with a hot flame ? The children will readily perceive that carbon cannot be used for this purpose as it would soon be burnt up. Something must be chosen which can shine without burning away. Only some ashy mineral substance will serve. And this realisation makes clear to the children the purpose and use of the incandescent gas mantle, for in this a non-luminous gas flame causes the earthy substance to glow white hot. The opposite of this is found in the carbon filament bulb, in which the carbon is caused to glow by an electric current, but cannot burn because all the air has been pumped out of the bulb. Thus in the case of the bulb, something inflammable glows but cannot burn, while in the case of the mantle the non-luminous gas flame causes something non- inflammable to shine.
The most various technical uses of flame may be simply explained to the children in this way.
Inflammable substances, such as sulphur and phosphorus which are of inorganic origin, and natural coal should be compared with them.
Sulphur is yellow; there is fire in it. When ignited it burns with a peculiar dark blue or light blue flame. This flame looks just like the blue part of a candle flame if it could be seen by itself. Sulphur comes out of the interior of the earth. For the most part it forces its way out through volcanoes. It is petrified fire which has burst out from the earth. By speaking of sulphur in this way, the children are brought to realise that the piece on the table before them is just a tiny portion of the fire process in the earth’s interior. Sulphur acts similarly both in plant and man. The colour of a field of rape might be mentioned and the fact that these plants yield a sulphurous oil. Both the hot-tasting radish and mustard contain sulphur. In man it has the effect of hastening metabolism. Sulphur baths have a healing action in cases of indurations, rheumatism and the like. But the sulphur often has the effect of making diseases which have long been slumbering in the patient, break out again. Skin eruptions may also result and old wounds break open. Thus in man, too, sulphur acts on the bodily functions in an inflammatory, volcanic way.
Phosphorus is quite different. Its flame shines brightly, almost like the sun. It shines even in the dark.
The children are thrilled when first they see that you can write on the blackboard in the dark with a piece of phosphorus and that the shining letters remain. They say: ” This is not matter at all, it is light.” And there is no heat either. The antithesis between the dull, blue flame of the sulphur and the white flame of phosphorus, is remarkable. It is as if the upper shining part of the candle flame were burning independently. Phosphorus is found in the brain of man. It has such light-giving power and works in the head! What is it doing there ? When we think, there is light in our brains and phosphorus is needed for this. Phosphorus has a peculiar smell, the same we notice after a thunderstorm. It alters the air in the same way as lightning. In a thunderstorm the lightnings flash down from heaven as though something were trying to shine into the world from the outer universe. When a volcano erupts something hot surges up from the subterranean, and there is a smell of sulphur. But when the lightnings flash there is a smell like burning phosphorus. And what does one say when an idea strikes one or one has understood something ? One says: ” A light dawns on me.” It flashes into the mind like lightning! This has to do with the phosphorus which is present in the brain. Yes, phosphorus is heavenly fire on earth; but sulphur is subterranean fire. Sulphur is found in the natural state as a product of volcanic action, but phosphorus has to be made artificially.
Coal stands half-way between these two inflammable substances. We are already aware that coal is dead vegetable matter. It has therefore its origin in life and so is inflammable. But it keeps its light hidden within. It is bewitched, and so it is itself black and dark. It has been formed within the earth. When coal is burned we get the ordinary kind of flame which shines above, and is blue below. In it are united the two kinds of flames found separately in sulphur and in phosphorus. And so it is with all living flames, for they all contain carbon.
Having shown the action of these substances in the universe their connection with man is again explained. Sulphur is active in the lower organs of man. It acts outwards and upward through the digestion, by way of the blood. It is a fire burning in man’s inward parts. But the cold light of phosphorus acts in the brain. We think with it. And what is the place of carbon ? We burn carbon within ourselves and breathe it out through our lungs. More about this will appear when we study carbonic acid gas. Through the helpful action of sunlight, plants breathe in the carbon. Flames breathe the carbon out again. Such an exposition will awaken a living consciousness that the three most important inflammable substances, i.e, sulphur, phosphorus, and carbon are associated with quite independent activities in man. Sulphur with digestion, carbon with respiration, and phosphorus with the light of thought which originates in the brain.