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The Wonder Book of Chemistry by  Jean Henri Fabre

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T would be a grave error, my young friends, to regard chemistry as nothing but a succession of experiments for amusing us in our leisure hours. There is, I admit, hardly anything that is more entertaining that to see a ribbon of iron burning brightly in oxygen, or to send up a little balloon inflated with hydrogen and then make it explode with a bang at the touch of fire. If such tricks as these keep the mind wide awake, so much the better, and what we learn through them will be all the more deeply impressed on the memory; but beware of imagining that chemistry ends there. The pursuit of this science is no such paltry affair; it is a very serious business, and has to do with all that concerns us in the material universe. To-day it is to show us why wine, cider, beer, and other fermented drinks foam.

"There are effervescent wines,—that is to say, wines that make the cork pop out of the bottle and are covered with foam when poured into a glass. To obtain such wines, we bottle them before fermentation is finished. Carbonic-acid gas thus continues to form in them; and as its outlet is closed by the cork stopper, it is forced to remain in the liquid, where it accumulates, but never desists from its [312] attempt to escape. It is this gas that makes the cork op out with a sharp report when the wire or string holding it securely in place is cut; and this it is, too, that sends the wine foaming out of the mouth of the uncorked bottle and makes the froth on the surface of the liquid in the glass, where it causes a slight crackling sound from the continuous bursting of little gas-bubbles. It is this same carbonic-acid gas, again, that gives its foam to cider, which, as you know, is simply fermented apple-juice; and to it is due the froth on beer, a drink made from barley in a sprouting condition."

"Sparkling white wine and cider," observed Jules, "have a sort of sharp taste, but it isn't disagreeable. I don't know anything about beer, for I have never tasted it. Does that sharp flavor come from carbonic-acid gas?"

"Yes. Carbonic acid is a very mild acid, it is true, but still it has the flavor peculiar to all acids, though in a very moderate degree."

"Then we swallow some of this gas when we drink wine or cider or beer, though it is a gas that can kill people if they take a few breaths of it."

"Carbonic acid is dangerous only when taken into the lungs in some quantity. To our fermented drinks it imparts a slightly acid flavor, not disagreeable, and even wholesome, for it aids digestion. You are to understand that such a substance, though capable of killing when breathed, can be quite harmless to the stomach. No one would venture to hold mouth and nostrils under water for any [313] length of time; the result would be death from suffocation or, as we say, drowning. Water is unfit for breathing, it cannot supply the place of air in our lungs; but, for all that, it is the very best of drinks. Carbonic-acid gas is somewhat like that: it can be drunk when mixed with a beverage, such as wine or cider; but whoever should undertake to breathe it freely would very soon die.

"There is carbonic-acid gas, supplied by nature, in nearly all the water we drink; and it is partly to this gas and its chemical action that we owe the stony material that we take into our stomachs with the water, and whose office it is to contribute to the growth and maintenance of our bones. However clear it may look, the water we habitually drink is hardly ever pure; it contains foreign substances in solution, as is proved by the thin coating of stony matter that gradually accumulates on the inside of carafes and dims the transparency of the glass. This coating is very hard to remove, as it seems to become one with the vessel to which it adheres. Sometimes it is necessary to use strong vinegar to take it off and restore to the carafe its former transparency. This coating is so resistant because it is of stone, real stone, similar in kind to that used by masons for building; in short, it is limestone. Thus the clearest water, water that shows no impurities whatever, nevertheless may contain stone in solution, just as sweetened water contains sugar, though it cannot be seen."

[314] "Then," said Emile, "when we drink a glass of water we drink with it a tiny bit of building-stone. I should never have suspected."

"It is very fortunate, my young friend, that we do thus drink a little building-stone, as you express it. Our bodies, in order to grow big and strong, need a good supply of stony matter for making bones, which are to us what its timber frame-work is to a building. This material that is so necessary to us is not made by us, but we get it from our food and drink. Water does its part in giving us limestone. If it did not contain this substance in solution, our bones, which are made chiefly of this material, could not develop properly and we should be puny and weak.

"A simple experiment will show us how limestone dissolves in water. Here in this small bottle is a little clear lime-water. Into it, down to the very bottom of the bottle, I thrust the escape tube of our carbonic-acid-gas apparatus. As fast as the gas passes through the tube into the liquid the latter becomes clouded and whitish. We know the reason: the carbonic-acid gas combines with the lime in the water to form carbonate of lime, limestone, chalk. So far there is nothing new; but let the gas go on discharging itself into the lime-water, and when it finds no more lime to combine with, it will become absorbed in the water, if not wholly at least in pat. Then we shall see the liquid lose its milky cloudiness, gradually turn clear, and finally become as transparent as it was in the beginning.

"Now it is done, the cloudiness has gone, the [315] white flakes have disappeared. The chalk is no longer to be seen, and the water has turned clear again. Yet we are none the less certain that in this liquid, in which there is nothing to be seen, there is still the carbonate of lime formed a few minutes ago; but it is in solution and therefore invisible. We have learned something new: water that holds carbonic-acid gas will dissolve a small quantity of limestone.

"Something else we are to learn, and then my demonstration will be finished. If this clear water with carbonate of lime in solution were allowed to stand a few days, the carbonic-acid gas would gradually escape, just as the same gas escapes from wine left standing for some time in a glass; and the lime, no longer held in solution by the presence of carbonic acid, would reappear as chalk-dust, and so the liquid would again take on a milky cloudiness. But this return to the milky state can be hastened: we have only to heat the liquid the drive out the carbonic-acid gas, whereupon the chalk again becomes visible and is deposited as a white powder. Thus it is made plain to us, first, that water containing carbonic-acid gas will hold a small amount of limestone in solution, and secondly, that this dissolved limestone reappears and forms a deposit as soon as the water loses its carbonic-acid gas either by long exposure to the air or by the action of heat.

"Now, carbonic-acid gas escapes from the soil in many places,—as, for example, in the Dog's Grotto with its stream of suffocating gas. Elsewhere the atmosphere always contains some of this gas, if [316] only what comes from the fuel burned in our fireplaces and stoves. Rain, in falling through and washing the atmosphere, and springs gushing up from under the ground thus meet with carbonic-acid gas on their way, and some of this they absorb and carry along with them. Afterward, as they flow over the soil, they are likely to become charged with limestone, which occurs in widespread abundance. Such is the origin of the carbonate of lime found in solution in most water. If now the carbonic-acid gas escapes, little by little, from prolonged exposure to the air, the carbonate resumes its stony form and is deposited on whatever objects may be in the water. In this way are formed the calcareous incrustations, or limestone coatings, that line and sometimes stop up our water-mains and the conduit pipes of fountains.

"To be potable—or, in other words, to be fit for drinking— water should contain a little limestone in solution; and after what I have just told you about the formation of our bones, you will see plainly enough the reason. But when it contains too much, it is hard to digest and oppresses the stomach. The proper proportion is from one to two decigrams, or about a pinch, to a liter of water. Where there is more, the water is what we call hard; or we say it is heavy, because it weighs on the stomach after being drunk.

"Water is sometimes so rich in limestone that it quickly encrusts any object immersed in it. You may have seen springs or brooks that coat with stony matter any blades of grass or tufts of moss [317] they may encounter in their course, forming thus a kind of light rock called tufa. Some of these calcareous springs are quite famous, as, for instance, that of Saint Allyre at Clermont-Ferrand. The water from this celebrated spring falls on a tangle of brush and is thus turned to spray, which is put to service by persons having objects they wish coated with limestone, such as birds' nests, baskets of fruit, bouquets of foliage and flowers. The carbonic-acid gas that helps to hold the limestone in solution escapes, and the spray deposits a coating of stone, so that birds' nests, baskets of fruit, and bouquets, all appear to be petrified. One would almost think a clever sculptor had carved these objects out of marble. Needless to add, such water is not suitable for drinking."

"I should say not," Emile agreed; "the stomach would get a lining of stone, which would not be very easy to digest."

"The water we use for household purposes never contains such an abundance of stony matter, but it often does have enough to cause inconvenience, especially in washing. You must have noticed that water in which linen has been washed with soap is more or less whitish. This whiteness is not due to the soap, for in pure water, such as rain-water, soap dissolves with hardly any effect on the transparency of the liquid, certainly without turning it to a milky whiteness. If ordinary water whitens with soap, it is due wholly to the stony matter in solution. When water whitens a good deal in laundry work and is filled with clots of soap, it is a sure [318] sign that it contains too much mineral matter. Washing is then rendered difficult, and soap dissolves poorly and is wasted in forming flakes without acting on the impurities in what is being washed.

"Water of this sort is bad, too, for certain kinds of cooking, especially for boiling vegetables such as dried peas, beans, lentils, and chick-peas, more particularly the last named. The stony material in the water impregnates the peas or beans or other vegetables, and you could boil them all day without making them soft. Water of this kind is, of course, as unfit for drinking purposes as for cooking; it overburdens the stomach with its excess of mineral matter.

"Now that we are on the subject, let us finish enumerating the qualities that water should have in order to be good for drinking. It should hold in solution a little air. We will heat some water, and as soon as it begins to get hot we shall see tiny bubbles rising from the bottom. These bubbles are not bubbles of steam, for the temperature is not yet high enough to make steam. They are bubbles of air, air that was held in solution and is now driven out by the heat. Well, this dissolved air is essential to water used for drinking. If it is not present, the water is somewhat disagreeable to the taste and may even provoke nausea. That is why tepid water that has recently cooled down from the boiling-point is not good to drink. The best water, then, is spring water, running water, because its continual motion brings it into contact with and enables it to absorb the greatest possible amount of air. Stagnant [319] water, on the contrary, water that stands still in some ditch, we will say, and is brought but little into contact with the air, is of inferior quality and often positively injurious to the health, especially when decaying vegetable matter is found in it.

"Ordinary water, as I have said, nearly always has a little carbonic-acid gas in solution. I will add that certain springs contain so much that they effervesce and have a slightly acid taste. These are called effervescent mineral springs, and to them belong Selzer, Vichy, and other well-known springs. The water from these is often used for medicinal purposes.

"But enough on the subject of carbonic-acid gas in water. Let us conclude to-day's lesson with a few words on the dangers that lurk in gases composed of carbon combined with oxygen. I say 'gases' and not 'gas,' because the combustion of carbon produces two combinations differing from each other in the amount of oxygen they contain. The one that is burned the more,—or, in other words, oxidized the more, and so is the richer in oxygen,—is carbonic-acid gas, with which we are now well acquainted; the one that is burned less completely, and so is less rich in oxygen, is called carbon monoxid. Unquestionably the first named is a formidable gas and one to be guarded against, as it is likely to accumulate where it will be a menace to human life, and does so to a notable extant in wine-cellars. Any one forced to breathe such an atmosphere even for a few minutes would surely die unless there were help at hand to resuscitate the [320] victim. Yet carbonic-acid gas is not a poison. We drink a little of it in ordinary water, and much more of it in effervescent drinks; we eat it, so to speak, in our daily bread, which is full of pores made by this gas when the dough is fermented; we breathe it constantly, as it is always present in the atmosphere about us; and finally, the human body itself is a perpetual source of carbonic-acid gas throw off in breathing. It is plain, then, that it is not a poison. If it causes death on being breathed in an unmixed state, that is due to no injurious properties in the gas itself, but merely because it cannot supply the place of air, the only breathable gas we have any knowledge of. Nitrogen will cause death in the same way.

"Carbon monoxid is quite different: it is really poisonous, a very harmful gas that acts fatally even when breathed in only small quantities and mixed with a good deal of air. It is the more dangerous in that it forms daily in our houses and nothing shows its presence. It is invisible and odorless, an enemy that makes itself known only when the damage has been done. We hear from time to time of some unfortunate person who, either by inadvertence or, as occasionally happens, by intention and from lack of courage to continue the battle of life, dies an untimely death in a closed room containing a charcoal heater. Carbon monoxid is the cause of those lamentable occurrences. Inhaled even in a small quantity, it provokes first a violent headache and general discomfort, then loss of feeling, giddiness, nausea, and extreme weakness. [321] While this state continues life is in danger, and death may come at any moment.

"It will be well for us to know under what conditions this terrible gas is produced. Since carbon monoxid is carbon less completely burned than when it becomes carbonic-acid gas, it is plain that what ever hinders combustion without stopping it entirely tends to produce this gas. If the draft is poor, if the burning fuel lacks a sufficient supply of air, carbon monoxid is the inevitable product of this imperfect combustion. Remember what takes place when a coal fire is started in a furnace. At first, the greater part of the fuel being cold and the draft of air being sluggish on account of this low temperature, combustion is slow and little tongues of blue flame make their appearance. Later, when the fire is burning briskly, these blue flames are no longer to be seen. Well, these tongues of flame having that beautiful azure color indicate the presence of carbon monoxid, for this gas shows that color in burning completely and changing to carbonic-acid gas. Whenever you see blue flames over a mass of burning coal, you may be sure carbon monoxid is feeding those flames.

"I have now told you enough to make you understand the risk we run when coal or charcoal is burned in such a manner that the products of combustion escape into the room where we are, instead of passing up the chimney; and the risk is all the greater if the room is small and tightly closed. Such a room should never be heated by a brazier, in which combustion is always sluggish, and which [322] always gives out more or less of this fatal gas that does not betray its presence by any sign, but comes upon us treacherously and by surprise. Death may occur even before any danger is suspected. The headache often felt when one is near a stove or a brazier, or even a foot-warmer containing live coals, is the only warning this terrible gas gives. Let us heed this warning and look to our safety.

"It is always very imprudent to close the damper of a bedroom stove in order to keep a low fire during the night. The smoke-pipe being thus closed by the damper and affording no sufficient outlet for the products of combustion, the draft is checked and carbon monoxid forms and spreads through the room, suffocating the sleepers. If a room is small and unventilated, a foot-warmer containing live coals is enough to give a headache and even cause more serious results."

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