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The Wonder Book of Chemistry by  Jean Henri Fabre


 

 

SULPHUR

[345]

"S
ULPHUR is so well known to you that I need not describe it. It is found chiefly in the neighborhood of volcanoes, where masses of it are unearthed, sometimes in a perfectly pure state, sometimes mixed with soil and stones. In the latter case it has to be freed from impurities.

"You have seen sulphur burning in oxygen with a beautiful blue flame. This combustion produces a gaseous compound of an intensely strong and penetrating smell and provoking a cough when breathed; and we call this gas sulphurous oxid. In ordinary air sulphur burns more slowly, less brightly, but is nevertheless gives the same compound in the end. It is this sulphurous gas that makes us cough when near burning sulphur, even if it be only the small amount of it in a friction match. What use can we make of this disagreeable gas, the merest whiff of which sets us to coughing as if with the whooping-cough? What service can it render us? That shall be the subject of our lesson to-day. But first go out into the garden and pick me some violets and a rose."

These were promptly brought to Uncle Paul, who then placed a little sulphur on a brick, lighted the [346] sulphur, and held over the flame the bunch of violets, having first moistened them slightly. In a few moments the flowers thus subjected to the action of the sulphurous fumes lost their color and turned quite white. The passing from blue to white could be seen very plainly, and it did not fail to call forth Emile's usual expression of surprise.

"Oh, how funny!" cried the boy, watching the process closely as his uncle held the violets in the gas rising from the burning sulphur. "See how white they turn as soon as they are in the smoke. Some are first half-white and half-blue, and then every bit of blue fades away and the whole bunch is pure white, with the flowers looking almost as fresh as before."

"Now let us try the rose," continued his uncle.

Accordingly, the rose was held over the burning sulphur, whereupon its red color faded in the same way and gave place to white, much to the satisfaction of Jules and Emile, who were already planning to repeat for themselves this wonderful experiment in bleaching, so easy to perform with a piece of sulphur and a few flowers.

"So much for that," concluded their uncle, giving the boys the bleached rose and violets to examine at their leisure. "What I have just done, you yourselves can do with countless other flowers, particularly red and blue ones; they will all turn white on being exposed to the sulphurous gas. Henceforth you will know that the pungent vapor of burning sulphur has the peculiarity of destroying certain colors [347] and, consequently, of leaving whiteness in their place.

"This peculiarity is turned to account in many ways, even having its uses in the household. Let us begin with the simplest of these applications. Here is a piece of white cotton cloth, percale. I stain it with the juice of a very ripe cherry. Now what we have to do is to take out the stain. It would be an all but hopeless task to attempt this with soap, but sulphur smoke will do it perfectly and promptly; for as it bleaches flowers so easily is must also take out a spot made by cherry juice, both flowers and cherries being dyed with a vegetable pigment. I moisten the spot slightly and hold it over a small piece of burning sulphur. To direct the fumes more directly upon the desired spot, I cover the sulphur with a small paper funnel, inverting it so that it may serve as a chimney, and I see that the spot is just over the outlet of this funnel. In a moment or two the reddish tint fades and gives place to white, just as did the color of the rose and that of the violets treated in a similar manner. All we have to do now is to rinse the bleached part in pure water. With this precaution the spot will not reappear. That is the way to treat wine stains, which are so hard to remove b y washing, and all spots made by preserved fruit with red juice, such as grapes, currants, strawberries, mulberries, blackberries, raspberries, and the like.

"Let us go on to another application even more interesting. After all possible washing, neither silk [348] nor wool, as they come to us in their natural state, will show that perfect whiteness so necessary if they are to reflect in unimpaired brilliancy and purity the dyes with which they are colored. Nor has straw used in the making of hats the desired whiteness; and the same is true of skins for the manufacture of gloves. Well, to whiten wool, silk, straw, and skins—that is, to bleach out their natural yellowish tinge—we treat them as the violets and the roses and the cherry stain have just been treated. They are first slightly dampened and then hung in a tightly closed room in which a few handfuls of sulphur are burned in an earthen bowl. The room becomes filled with the sulphur fumes, and after a day or two the wool and silk and straw come out exquisitely white.

"Sulphur is used for many other purposes, including some that would hardly occur to you. It can even put out a fire. Yes, my little friends, sulphur, which itself burns so readily, will smother flames."

"But that," objected Jules, "is giving the fire more fuel, and one of the most inflammable of fuels, too. I don't understand it."

"You soon will. What does a fire need to keep it burning? Two things, the one as essential as the other,—fuel and air. Imagine a great fire. Is it not true that if we could cut off its supply of air it would speedily go out, and that this would be much better than pouring on water? Is it not true also that if, instead of giving it air, we could substitute a gas unfit for combustion, such as carbonic acid or nitrogen, the fire would not continue to burn another moment? A lighted candle goes out as soon as it [349] is immersed in either of these gases; and so would the best-fed fire in the world if it were suddenly enveloped by a similar atmosphere."

"I see well enough that if we could pour a perfect torrent of nitrogen or carbonic-acid gas on a fire, so as to crowd out all the air and completely surround the burning mass, the flames would be smothered at once; but we could n't do that."

"Not always. In the open air, I admit, it would be hardly practicable; but in a chimney-flue, for example, it is a different matter. There the fire is confined in a narrow passage to which air is admitted through only two openings, and more especially through the lower one. In such circumstances it is not impracticable to make a stifling gas take the place of the air that would otherwise gain admission. Suppose a chimney to catch fire. In order to extinguish the flames in the quickest and simplest manner, recourse is had to sulphur. Any gas unfit for maintaining combustion and itself incombustible would serve; but it is indispensable that this gas be obtainable quickly and in abundance, also at little expense and without the use of any apparatus. Nitrogen and carbonic-acid gas are here out of the question, as it is a difficult, slow, and costly operation to produce them. Sulphurous oxid, however, we can use, as it is instantly procurable if we have a handful of sulphur to throw on the burning coals in the fireplace under the burning chimney. No other gas could be so easily, quickly, and abundantly produced. On the burning brands in the fireplace we throw sulphur without stint, and then shut out the air by [350] stretching a wet cloth across the opening of the fireplace. The sulphur fumes pass up the chimney, driving out the air and so extinguishing the burning soot."

"All the same," said Emile, "it seems queer to put out a fire with sulphur. I should never have thought of such a thing."

"Still another use of this same gas is worth mentioning. It has to do with disease and its cure. We give the name of parasites to all kinds of little creatures that live on other creatures, usually establishing themselves on or in the victim's body. Despite the noble faculties that make him the king of creation, man himself plays his part as victim in this battle between the devourers and the devoured. He has his parasites that live on his substance, just as cherries and walnuts have their peculiar insect pests. Instances without number, alas, make it all too plain that the general rule is applicable to man without respect for his superiority in the scale of creation.

"Besides those powerful and ferocious animals like the lion and the tiger, in whose claws man is as a mouse in the cat's clutches—besides formidable species of that kind, which we can at least openly contend against—we are delivered over to famished hordes that by reason of their very smallness their multitude, and their secure retreat, are able to defy with impunity our efforts at self-protection. First it is the mosquito, armed with a poisoned lancet and sucking our life's blood from our veins without fear of reprisal, and sounding its war song in our ear sat night as if in mockery of our im- [351] potent wrath. This war-song is the sharp buzzing made by the insect as it approaches us and searches our skin for a suitable spot in which to plunge its lancet."

"How often I have slapped myself," said Emile, "trying to kill those hateful mosquitos when they came and sang their impudent song in my ears in the dark!"

"We have also the louse and the flea, the former attacking our head and the latter assailing the whole body with irritating bites. Like the mosquito, they are after our blood for food; and they get it, too, unless the utmost attention is paid to cleanliness.

"I pass on to another tiny man-eater. A microscopic little creature, and almost invisible parasite called the itch-mite, works its way into our skin, in which it tunnels passages somewhat as a mole burrows a field. Its mole hills are little pimples or pustules that cause acute itching. Such is the origin of the ailment known as the itch."

"You say itch is caused by a parasite that gets into the skin?" asked Jules.


[Illustration]

UNDER SIDE OF ITCH-MITE, HIGHLY MAGNIFIED.

"Yes, and the disease spreads by mere contact, as the parasite passes readily from one person to another, from an infected to an uninfected person."

"And what does it look like, this horrible little creature that makes people scratch so?"

[352] "It looks like a tiny white speck just big enough to be seen by the sharpest eyes, and it is round in shape, reminding one a little of the tortoise. It has eight legs, two pairs in front and two behind, all bristling with sharp, stiff hairs. When it walks it spreads out its eight legs; but in repose it draws them in under its arched body, very mush as a tortoise disposes of its legs under its shell. Finally, its mouth is armed with sharp hooks and fine nippers. With these tools it burrows here and there in the skin, making long passages in which it comes and goes at will, just as a mole does in the ground. The learned word for itch-mite means flesh-cutter. I leave you to imagine the unbearable itching this tunneler of human flesh cause when with its well-armed beak it cuts and slashes its way in this direction and in that."

"Don't talk of it any more, Uncle!" pleaded Jules. "It makes me want to scratch just to think of it."

"How is this odious parasite to be got rid of? It is hardly visible and lives inside the skin. Think of trying to catch it there, when it multiplies by the thousand. It is plain that no medicine taken internally will be of any use here. To cure the patient there is but one remedy,—kill the creature that causes the disease. But how kill it in its safe retreat? That is the problem. When a fox commits too many misdeeds and makes havoc among the neighboring poultry-yards, it is smoked out of its hole, stifled in its fortress with burning sulphur until it is forced to surrender. So, too, with the itch-mite. The patient is stripped and enclosed in a kind of [353] tank, his head alone remaining out to allow him to breathe, and then sulphur vapour is made to fill the tank. If this fumigation is properly conducted the insect pest gets enough of it in one turn: it perishes, stifled in its retreat, and the patient is cured. Truly, it is no small service for which he is indebted to the gas we complain of so loudly whenever the fumes of a lighted match tickle our nose.

"To finish our talk on sulphurous oxid, I will tell you about one of its commonest uses. You know how wine is made. I have told you how the sugar in the juice of the grape turns to alcohol by fermenting. Well, this fermentation may go too far, and then the wine sours little by little and turns to vinegar. To prevent this deterioration, the process of fermentation must be arrested; and this is done by burning sulphur in the casks that are to hold the wine. The sulphurous gas thus generated purifies the casks, even working its way into the wood, and stops the fermentation before it goes too far. Thenceforth there is no danger of the wine's turning sour.

"Sulphurous oxid is the only compound that sulphur forms when burned under ordinary conditions, a process you have already witnessed. But I have told you of an acid made from sulphur and containing more oxygen than is found in sulphurous oxid. It is sulphuric acid or oil of vitriol, which we used for decomposing water in order to obtain hydrogen. How, then, is this acid made, this compound of sulphur with an extra supply of oxygen, when we have seen that no matter how much air we give our burning sulphur we get nothing but sulphurous oxid?

[354] "Well, we resort to indirect methods much more powerful than simple combustion. There are, as you know, certain rich storehouses of oxygen,—that is to say, certain compounds in which this gas is found accumulated in unusual abundance, but not firmly fixed. Sometimes a little heat will suffice to set free this captive gas. It was thus that chlorid of potash, heated by means of a few live coals, was made to give us a supply of oxygen readily give up a part of their gas to substances that have either none at all or not enough; and to this class belongs nitric acid, or aqua fortis,  a very useful liquid for oxidizing substances or for adding to the oxygen already in them. If, then, nitric acid is made to act on sulphurous oxid, which is nothing but incompletely burned or oxidized sulphur, the latter takes on additional oxygen from the nitric acid and is changed into sulphuric acid. Immense factories with tall chimneys belching smoke, and with numerous furnaces for burning sulphur, are engaged in the manufacture of this acid, which is used in many branches of industry. Sulphurous oxid, made by burning either pure sulphur or iron pyrites, in which sulphur is abundant, is conducted into enormous leaden chambers shaped like our largest rooms. There it finds nitric acid, which gives up a part of its oxygen, and the transformation is quickly accomplished.

"Sulphuric acid is a heavy liquid, much heavier than water, and oily in appearance, whence its name of oil of vitriol. In a pure state it is colorless, but usually it is impure and of a brownish tinge. Mixed [355] with water, it generates considerable heat. When we were preparing hydrogen, our mixture of sulphuric acid and water became burning hot. The combustion or oxidizing of the zinc, at the expense of the oxygen in the water, had a good deal to do with this generating of heat; but the interaction of sulphuric acid and water had also a part in it. Let us study this latter process by itself.

"Into this glass containing only a little water I carefully pour some sulphuric acid and stir the liquid. The mixture becomes very warm, almost hot. Put you hand on the glass and judge for yourself. What can this heat signify except that a chemical union is taking place between the water and the acid? It shows us that sulphuric acid has a strong tendency to combine with water. The following is another proof of this tendency. Leave a finger's depth of sulphuric acid in a glass for a few days. At the end of that time the liquid will be found to be notably augmented in volume: instead of one finger's depth there may be two. This increase is due to the fact that the sulphuric acid has attracted and incorporated moisture from the surrounding atmosphere. Of course, in the process of gaining volume by taking on water, the acid also becomes weaker. Consequently, if sulphuric acid is to preserve its strength it should be kept in a tightly corked bottle.

"From this affinity for water comes one of the most remarkable properties of sulphuric acid. All animal and vegetable substances are composed chiefly of carbon, hydrogen, and oxygen. Well, if any animal or vegetable substance comes in contact [356] with sulphuric acid, the latter promptly seizes upon the hydrogen and the oxygen to form water, which it appropriates, leaving the carbon by itself exactly as if fire had acted upon the substance. Thus all animal or vegetable material subjected to the action of sulphuric acid is carbonized,—that is to say, reduced to carbon, so that one would think it had passed through fire. Here, for instance, is a pine chip. I immerse it in sulphuric acid and leave it alone a few minutes. You can see the wood turn black; it is reduced to carbon, or charcoal. Fire could not have done it more quickly.

"But I now come to an experiment that will be of even greater interest to you. Into five or six thimblefuls of water I put one drop of sulphuric acid, and no more. It makes a liquid that is unbearably sour like lemon juice, though it looks exactly like pure water. This perfectly colorless liquid I am going to use as writing-ink, very black ink. I take a goose-quill and not a steel pen, as the latter would be attacked by the acid and might discolor it somewhat. My paper is common white paper without any special preparation. Now watch."

Uncle Paul tore a piece of paper out of Jules's copy-book, dipped the goose-quill into the mixture of water and acid, and wrote something in characters that remained as invisible as if he had written in pure water. As soon as all traces of moisture left by the goose-quill had dried up, the paper was handed to the children.

"Read, if you can," said their uncle, "what I have written with my chemical ink."

[357] The paper was carefully examined in the light, first on one side, then on the other, then upside down, and then held against the light; but there was nothing to be seen, the writing being so completely invisible that it was impossible even to guess where the pen had been.

"Your very black ink is not the least black yet," said Emile, "I can't see anything, not the least thing, and if I had not seen you writing I should say this piece of paper had never been used."

"Nevertheless," his uncle assured him, "the invisible is going to become visible. I heat my paper by holding it before the fire. Watch what happens."

At the first touch of heat black characters came out on the white background of the paper as if by magic. Some appeared suddenly and completely, while others came out in separate bits that finally joined one another in unbroken lines, so that very soon there could be read in letters of a deep black: Carbonization by sulphuric acid.

"Wonderful!" cried Emile, as he watched the characters forming as if of their own accord. "Wonderful! Let me take your magic ink, Uncle, please; I want to show it to a friend of mine."

"You may keep the magic ink. Weakened as it is by so much water, the acid is no longer dangerous, even in the hands of a giddy-pate like you. Now for the explanation of this writing that so delights you. Paper is made of vegetable matter such as old rags woven of cotton that has first been spun into thread. Hence it contains carbon, hydrogen, and oxygen. Acted upon by the heat from a stove or an [358] open fire, the trifling amount of sulphuric acid in my colorless ink attracts the hydrogen and oxygen at the places touched by the pen, turns these two elements into water, which it appropriates, and leaves the carbon showing plainly in black letters. That is the whole secret. What was at first invisible now shows in marks of a deep black, because the sulphuric acid has laid bare the carbon in the paper.

"What I have just shown you is enough, I think, to make you understand how dangerous this sulphuric acid is, turning everything to charcoal as it does with as much ease as if, instead of being an acid, it were a scorching flame. Whoever handles it should do so with the utmost caution. A single drop on the clothes is first a red spot and then a hole. A drop on the skin is nothing if washed off immediately, but would inflict a very painful wound if left to take effect. It is the eyes, however, that have the most reason to fear this terrible liquid. The least splash of it would lead to the most serious consequences if water were not used at once and in abundance to wash it away.

"And yet this perilous stuff is constantly called into service in a number of industries. Manufacturers find it of the utmost value. Our woven fabrics, our various kinds of leather and glass and soap, our candles, dyestuffs, paper, ink—in fact, a multitude of manufactured articles in common use—all need more or less directly the services of sulphuric acid. I do not mean to say that this acid enters into the composition of a yard of percale, for example, or a sheet of paper, or a cake of soap. What I mean is [359] that its services have been required in the process of making this percale, this paper, and this soap. Sulphuric acid is a necessity in manufacture, an instrument of the most powerful kind, and one that works those transformations without which the manufactured article would never have come into being.

"Take glass as an example. It is made by fusing sand with carbonate of soda. Nature provides the sand all ready for use, but we have to manufacture the carbonate of soda. This is done with the help of sulphate of soda, which itself is obtained by subjecting salt to the action of sulphuric acid. Thus, while glass itself contains no sulphuric acid, this acid is nevertheless needed in the making of glass, as without it salt cannot be made to furnish its soda to the sand that, uniting with this soda, goes to the producing of the glass. A similar part is played by sulphuric acid in the making of soap, which contains a large proportion of soda. Coal for heating our factory furnaces and generating steam for moving the factory machinery, and sulphuric acid for working important chemical changes—these are tow of the most potent factors in modern manufacturing industry."


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