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The Wonder Book of Chemistry by  Jean Henri Fabre

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The Wonder Book of Chemistry
by Jean Henri Fabre
Starting with a mixture of iron filings and sulphur, Uncle Paul awakens in his young nephews an eagerness to learn more about the properties of the elements. Through a series of carefully-devised experiments and conversations about the experiments, he leads the boys to an understanding of some of the basic principles of chemistry. Excellent as a follow-on to 'The Story Book of Science' and 'The Secret of Everyday Things' by the same author.  Ages 11-15
379 pages $14.95   





N the following day Uncle Paul resumed his talk.

"This gas called oxygen," said he, "the object of our search at present in our exploration of the field of chemistry—have I lost sight of it by allowing so many stages to our journey and thus giving you time to look about and get your bearings? Have we been straying from the direct road? Not by a hair's breadth; we are nearing our goal; in fact, we have reached it. We have just learned that a salt is a storehouse of oxygen, that it is indeed doubly so, for its acid constituent is composed of this gas and a metalloid, while its oxid contains this same gas plus a metal. A salt, then, which unites in itself two burnt substances, is what we must go to if we wish to obtain the gas that makes things burn. Nevertheless we must use care in making our selection, for most salts stoutly resist decomposition and it is only with great difficulty that they can be made to give up their oxygen. We should have no better luck with them than with phosphoric acid or oxid of zinc. What they have once got they hold on to with a tight grip. Consequently, we should be at a loss what to do if chemis- [172] try did not tell us the salt to resort to. It advises us to try chlorate of potash as being rich in oxygen and easy to decompose."

A bottle containing a white substance in the form of little transparent scales was set before the boys.

"Here we have some chlorate of potash," their uncle announced. "It came from the drug shop where I bought our stick of phosphorus and some other materials needed in our lessons."

"That looks a little like salt," Emile observed.

"Yes, it looks like it, but its properties are very different. In particular, it has no salt taste; and also it contains oxygen in abundance, while kitchen salt has none at all. I must remind you once more that by an unfortunate accident of language the general term for all salts is taken from a substance that is not, itself, a salt according to the accepted definition; that is, it is not a compound of an acid and an oxid. I will also ask you to bear in mind that many salts have the colorless and glassy appearance of our common salt, and that this likeness, which is purely external, is responsible for the adoption of the term as used in chemistry."

"Then you say this white stuff, this chlorate of potash, has oxygen in it, the gas that makes things burn?"

"Yes, it has oxygen, and a great deal of it, too; so much, that in fact, that a little handful of this salt will give us several liters of pure oxygen. It is there, squeezed into a small space by being combined with other things. Go back to our grammar of chemis- [173] try, of which you have learned the most important rules, and it will tell you what chlorate of potash is made of."

"The word chlorate," replied Jules, "tells me that the substance contains chloric acid. What that acid is like I don't know, for I have never seen any; but I know at least that according to its name it has in it a metalloid, chlorin, and, besides that, some oxygen."

"Right here let me add," interposed his uncle, "that this metalloid called chlorin is also present in kitchen salt. That will help you to remember the name, which is so new to you, and the time will come before long when you will become better acquainted with the thing itself. What else does the name chlorate of potash tell you?"

"It tells me that the salt contains an oxid furnished by a metal called potash, if I am not mistaken."

"You are mistaken as to the name of the metal, but that is not your fault, for here we meet with an exception like that we found in the use of the word 'lime.' You have not forgotten that certain well-known oxids retain in chemistry their popular names. We say 'lime,' and not 'oxid of calcium'; and in similar manner we say 'potash' instead of 'oxid of potassium.' As to this metal potassium, it is really a metal, much like the metal element in lime, but even softer and quicker to catch fire in water. It is found in wood-ashes. But we need not discuss it further to-day; only notice, while we are on the subject, what curious facts are to be learned [174] from the commonest things when they are examined chemically. Thus, the salt we use in our cabbage soup gives us chlorin, a very interesting metalloid that Emile would not soon forget if he should venture to be too familiar with it; and the ashes from our hearth furnish potassium, a metal that catches fire at the mere touch of water. Briefly stated, potash is the oxid of the metal called potassium, and it is customary to say 'chlorate of potash', 'sulphate of potash', and so on, just as we say 'sulphate of lime' instead of 'sulphate of calcium.' So, you see, the salt we have here gets its oxygen both from the aicid it contains in the form of chloric acid and from that present in its oxid, potash.

"This salt decomposes readily, needing only heat to make it surrender all its oxygen. Look here a momment, and you will be convinced."

So saying, Uncle Paul dropped a pinch of chlorate of potash upon a handful of glowing coals, whereupon the chlorate of potash melted with much bubbling and foaming, while the coals all about it began to burn with extreme brightness and heat. It was as if a puff of wind had fanned the glowing embers, though no puff of wind could have been at once so noiseless and so effective. The intense burning went on with an energy astonishing to the young beholders.

"What splendid kindling that would make," Emile remarked, "for starting up a fire when it gets low! All you'd have to do would be to throw on a handful, and the wood or coal would be all ablaze. [175] You might work the bellows all day and not make it burn so."

"From the bellows," replied Uncle Paul, "comes only air, in which nitrogen, a gas that does not help things to burn, is much more plentiful than oxygen, which alone helps on the burning. In this mixture the inert or useless gas considerably weakens the effect of the active or useful gas. But chlorate of potash, on being decomposed by heat, sends out a breeze, as we might say, of pure oxygen; and that is why the coals here burned just now with so much intensity. With this kindling, as Emile calls it, a fire gains in vigor and rapidity because the gas it feeds upon is mixed with nothing to weaken its effect."

More pinches of the chlorate were thrown upon the coals, and when the two young observers had seen how this easily melted substance quickened the fire by the release of oxygen, which escaped in bubbles, Jules told his uncle of something he and his brother had once noticed with much curiosity.

"One day," said he, "I had taken a feather and swept off a handful of that white, moldy stuff that collects on cellar walls, when some one told me it was saltpeter and that saltpeter is used for making gunpowder. I dropped some on the live coals in the fireplace, and it made a quick, bright fire like that you made with the chlorate of potash. Does that fluffy stuff on damp walls give out oxygen when you put it on the fire?"

"The fine white flakes such as you swept from [176] the cellar walls are, in truth, saltpeter,—or, in chemical language, nitrate of potash. This substance is, as its name shows you, a salt, containing oxygen in its acid part, which is nitric acid, and also in its oxid, which is potash. When you throw it on the fire it decomposes, releasing its oxygen; and that explains why it makes any burning substance burn so much faster than before. Thus, the saltpeter from damp walls acts in the same way as chlorate of potash; they both decompose, and in so doing give out in abundance the gas needed to make fire burn. I must let you know, however, that nitrate of potash is not a suitable substance from which to obtain oxygen, because it is not so readily decomposed as Jule's experiment would seem to indicate. To make this nitrate surrender its oxygen heat is not enough; it also requires some combustible matter, as wood or charcoal. Then the fuel seizes upon the oxygen as fast as it is released, and so the gas escapes us again, being taken and held captive in another compound. Consequently, nothing has been accomplished; what we wished to obtain has slipped out of our grasp and entered into a new combination. With chlorate of potash, on the contrary, heat alone is enough for our purpose, without the help of anything else that might appropriate the oxygen released by the salt."

"Another question," said Jules.

"As many as you like, my young friend. I shall take pleasure in answering them, for I know beforehand that they will be well-considered questions, coming as they do from a thoughtful mind."

[177] "When you threw the chlorate of potash on the coals, it first melted, then bubbled and let go its oxygen, and at last there was nothing left of it but a little white round piece that would n't burn at all. What is that white stuff that is left on the coals?"

"Your question is well put, for it concerns a rather important matter. I had forgotten to explain this, but now I will repair the omission. This remainder, this bit of white crust that fire has no effect upon, comes from the chlorate of potash when the latter is decomposed by heat. What did this chlorate contain to start with? Three elements, the chlorin in the chloric acid, the potassium in the oxid of potassium, and the oxygen in both. Of these three elements, one, oxygen, has disappeared. There remain then, the chlorin and the potassium, united in a compound very different from the original chlorate. This compound is called chlorid of potassium.

"This gives me an opportunity to teach you a new rule in the grammar of chemistry. The various metalloids can combine, one by one, with the various metals. In the case of oxygen, for example, the combination with a metal is called an oxid, as you already know; and so of the other metalloids, sulphur, chlorin, phosphorus, etc., the name of the compound is formed by adding the ending id  to the name, or the chief part of the name, of the metalloid, after which comes the name of the metal preceded by the preposition of. In the substance before us we have chlorin and potassium in combination; in other words, we have chlorid of potassium. [178] But enough of this, and perhaps too much; let us return to the subject of oxygen.

"We have to find out, if possible, how an unskilled experimenter may hope to obtain, without too much difficulty, the gas stored up in the chlorate of potash. He should first procure a glass receiver of some sort, and in this the decomposition is to take place. A medicine-bottle, short and as wide as possible, will answer the purpose, provided the glass is not only thin, but of uniform thinness throughout. A glass vessel exposed to heat will remain unbroken only if it complies with these requirements. The thinner it is, the less likely is it to break under sudden variations of temperature. Look at this tumbler here: at the bottom it is as thick as your finger, but it is thin elsewhere. Plunged cold into hot water, or hot into cold water, it would run great risk of breaking. On the other hand, a piece of glass of even thinness comes out intact from a similar test. Let us, then, choose the thinnest bottle we can find, and above all one that has no thick places in the glass as are often found in the bottom of an ordinary bottle. The success of our experiment depends greatly on our choice."

"I should have thought," said Emile, "a thick, strong glass would be the kind to use. It would stand the strain better."

"Yes, if it were a question of resisting shock or of not melting under heat. But here it is not a question of resistance to shock, as I take for granted the operator is sufficiently skilled not to bump his [179] receiver against any hard object; nor is the danger of melting worthy of consideration, the heat required for decomposing chlorate being insufficient to fuse or even soften the glass. Our bottle, then, will not have to bear any excessive heat, though it will undoubtedly undergo changes of temperature sudden enough to break it unless we guard against such an accident by selecting a bottle of very thin glass."

"But what if, after all, the bottle full of chlorate should break over the fire; what would happen then?"

"Nothing very serious. We should simply have to let it alone and watch the beautiful fireworks resulting from the release of so much oxygen on burning coals. We should witness on a large scale what you saw when I put a few pinches of the chlorate on a handful of glowing embers."

"And then?"

"Then we should begin again with another bottle; that's all. But better than a medicine bottle, which I should unhesitatingly use if I had nothing more suitable, is a receiver called in chemistry a balloon. It is a vessel of clear glass, round in shape, with a neck about as long as your hand is broad, and it can be had for a few cents at the druggist's, or some chemist might spare us one from his laboratory. Here is the balloon we are going to use; it is one of my recent purchases in town."

"That looks like one of those candy bottles they always have for selling candy to the children at [180] village fairs. For two cents you can buy the whole thing, candy and bottle and all."

"Your candy bottle would do very well here if it were larger; but what could not well be replaced by anything else is the tube for conveying the gas from the balloon into the bell-glass. The tube is made of glass, and may be had of the druggist, who will perhaps furnish the complete outfit we need, all ready for use, or we might apply to some chemist friend. But, after all, our best course is to make our apparatus for ourselves, and then we shall be sure to have it in all respects as it should be for the successful performance of our experiment. At the druggist's we find straight glass tubes of a meter and more in length. We select several about as large round as a lead pencil and made of thin and colorless glass, which softens much more readily with heat than does greenish glass. Let us examine the thickness of the glass. If in cross-section it looks thin and colorless, it is what we, with our limited resources for working in glass, are seeking. A thick green glass would be too unmanageable for us. Providing ourselves, therefore, with a few of these straight tubes of thin, clear glass, we next proceed as follows:

"To cut from the straight tube any desired length, we first take a triangular file and make a little groove all around the tube at the point where it is [181] to be broken, then, taking the tube in both hands, we hold the grooved part against the edge of a table and exert a gentle pressure. The break is made instantly, round and clean. Now it remains to fashion this broken-off piece so as to give it the shape suitable for our experiment. All we have to do is to bend it at various points after first softening it at those points by heat. With easily melted glass this may be done with the help of a handful of live coals blown to glowing heat by the breath; but the operation goes better if we use an alcohol lamp. This is simply a metal or glass cup or holder containing alcohol into which runs a wide cotton wick, the exposed end of which runs a wide cotton wick, the exposed end of which is lighted. The part of the tube to be softened is held to the flame by taking one end of the tube in each hand and turning it between the fingers so that the heat may get at it all round. As soon as the glass seems soft enough to bend, a slight exertion of strength will produce the elbow desired, which may then be left to cool off slowly.


"The tube thus bent is to be attached to the balloon by means of a stopper with a hole through it, the stopper being one that fits tightly and allows no gas to escape. This perfect stoppage is necessary in handling oxygen and other gases, so subtle is their nature. The smallest possible opening is big enough for them to get through. Hence the stopper must be fitted with extreme nicety. I will explain how to do it.

"Select a stopper of fine cork, as uniform in its structure as possible, and without any of those [182] holes or decayed spots that are found in cork of poor quality. With some heavy object, the first to come to hand, such as a round stone or a hammer or anything else of the sort, first give the stopper a few light blows to soften it and make it supple. Then with a coarse iron wire pointed at one end, and heated red-hot if you choose, for the sake of easier and quicker execution, pierce the stopper lengthwise, making a small hole for the guidance of the file with which it is to be enlarged. This latter, called a rat-tailed file from its shape, is round and should not be of greater caliber than the tube that is to pass through the cork. With this file` you then carefully enlarge, perfect, and smooth the channel in the cork until the tube will pass through under gentle pressure and fill it exactly. Now take your cork in hand again and shape the outside to fit tightly into the neck of the balloon. With a coarse flat file you first rasp it lengthwise to make it regular in shape and slightly tapering. When thus reduced to the proper size, it is finished off with a finer file, being worn down and smoothed until it fits perfectly into the neck of the balloon. Observe that no knife or other edged tool, however sharp, could do the work of the file in thus preparing the stopper, for the cork would be cut unevenly and the result would be an escape of gas. An accurately fitting stopper is indispensable to success. In future, then, we will count as necessary to our laboratory equipment four files,—namely, a fine triangular one for notching the glass tube so that any desired length may be broken off; [183] a round one for enlarging the hole made in the cork by the iron wire; a coarse flat one for rasping the outside of our stopper and giving it a preliminary shaping; and, lastly, a fine flat one for finishing and smoothing."

During these explanations the speaker's hand helped out his words, example accompanied precept, and the tube was bent in the flame of the alcohol lamp, the stopper was pierced and filed and finished, and in a short time everything was in readiness.

"Our apparatus is now in order," said he, "and we will put it to use. But first a brief word of explanation will not be out of place. Heat alone suffices to decompose chlorate of potash and make it give up its oxygen, although toward the end of the operation the salt becomes obstinate and, in order to obtain all the gas, must be heated to such a temperature as would endanger our balloon by softening the glass. I hold it of the first importance, and you will agree with me, that we should not damage our apparatus, as our resources do not admit of our sacrificing a balloon every time we want a little oxygen. Besides, it is much more convenient to operate with less heat. Well, then, chemistry tells us that by mixing the chlorate with some black substance that will distribute the heat evenly throughout the whole mass the complete decomposition of the salt may be easily accomplished. A handful of live coals will under these conditions give enough heat, and the balloon will not be exposed to any danger.

"My speaking just now of a black substance perhaps made you think of coal-dust. Beware my dear [184] boys, of mixing anything of that sort with the chlorate and then heating the mixture, if you do not wish to be disfigured by a violent explosion. Those two substances make a dangerous mixture. And why? The reason is plain. On being heated, the chlorate gives out oxygen, and this gas, mingling with an inflammable powder such as coal-dust, will not fail to produce a sudden explosion that would blow our apparatus to pieces. Nothing that can burn should be mixed with the chlorate, the risk involved being too great. Bear this well in mind.

"What, then, shall be the black powder for making quicker and easier the decomposition of our chlorate? It must be something that will not burn; something that, having already been burned, that is united with oxygen, will no longer catch fire. The best thing for our purpose is a metal oxid. There is found in certain mines—and the druggist sells it for a trifle—an intensely black powder called dioxid of manganese. Manganese itself is a metal much like iron, rarely found in a pure state, and hardly ever used in that form. United with oxygen, it forms various compounds, the second of which in abundance of oxygen is the dioxid I have mentioned, which is what we require for mixing with our chlorate to help on its decomposition. With this black substance we incur no risk; fed up, so to speak, with the gas that makes things burn, it can take on no more, a fact that removes all danger of any excessive combustion within our apparatus.

"Accordingly, I place on a sheet of paper a good-sized handful of chlorate of potash, a little less of [185] dioxid of manganese, mix the two together, and pour the mixture into a balloon of the size of a large orange. The tube with its stopper is then adjusted, and the apparatus, supported by a triangle of stout iron wire, is placed on a brazier.

"Here will occur a slight difficulty that must be overcome before we can proceed. Our oxygen is to be collected in wide-mouthed bottles or jars, full of water and inverted in the bowl of water so as to bring the free end of our glass tube directly under the mouth of the inverted bottle or jar, and the latter must accordingly be held in a tilted position. But this is tiring to the arm if the operation is of any length, and it would be better if the inverted bottle could be made to stand erect on some support. But how, in such a position, can a passage be left open for the end of the tube conveying the gas from the balloon? Nothing simpler. Let us take a small flower-pot having a hole, as is usual, in the bottom; then by breaking off some of the upper part of the pot we can lessen its height and obtain a sort of cup only a few fingers tall. No matter if the edge of this cup is irregular or even jagged; it will do if it stands firm and if it is upturned bottom offers a level support for the inverted bottle or glass jar. Finally we make a deep notch in the side, and the support for our bottle is ready. We place it in the middle of the bowl, the flat bottom upward, and through the notch in its side we pass the end of our glass tube, which will thus emit the released oxygen within the enclosure of the supporting pot. On the latter will rest the inverted bottle [186] or jar full of water, and the gas will gain access to it through the round hole in the support.

"Enough, my little friends, on this subject. Our apparatus is harder to explain than to make. I promise you for to-morrow some experiments that will richly repay you for the dry preparations of to-day. And now get me one more sparrow, if you please. Set your snares in the bed of peas. As the captive bird will not share the sad fate of its predecessor, there is nothing to dread in our coming experiment."

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