Home  |  Authors  |  Books  |  Stories  |  What's New  |  How to Get Involved 
   T h e   B a l d w i n   P r o j e c t
     Bringing Yesterday's Classics to Today's Children                 @mainlesson.com
Search This Site Only
 
 
The Wonder Book of Chemistry by  Jean Henri Fabre

[Illustration] Hundreds of additional titles available for online reading when you join Gateway to the Classics

Learn More
[Illustration]

 

 

SALTS

[154]

T
HE white substance left by the burning magnesium had been wrapped in paper, and Uncle Paul took it up again as his opening topic in the next lesson.

"Judging from looks only," said he, "we compared this powder to flour and also to very finely ground chalk. If we considered its properties, we ought rather to compare it to lime. This latter, at first a rough and shapeless stone, swells on being soaked in water, and then cracks to pieces and turns into a white powder closely resembling burnt magnesium. Nor is this resemblance misleading, for chalk is also a burnt metal."

"A burnt metal!" repeated Emile, in surprise. "I never knew chalk was made by burning a metal."

"Naturally not," replied his uncle, "for that is not the way it is obtained. If, in order to get lime, we had to burn the metal that enters into its formation, the mason would never venture to use a trowelful of mortar, because of its excessive price."

"I know how lime is made," put in Jules. "Out in the country they pile up stones and charcoal in a lime-kiln, and the fire bakes the stones and turns them to lime all ready for use."

[155] "That is it. The stone they use is called limestone, and it contains lime and something else; this latter the fire drives out, so that, after the burning is finished, the lime is left by itself, ready for the mason and very different from the original stone. It is really a burnt metal, though the lime-burner knows nothing about the burning of metals, and does not even suspect the presence of a metal in the product of his kiln. The honest lime-burner would be greatly surprised to be told that his lime contains a metal; he would laugh in your face and say you were joking. But nothing could be further from joking; lime comes from the burning of a metal or, in other words, from the combining of a metal with oxygen. Its particles may be likened to the tiny scales that fall from red-hot iron as it comes from the forge, and to the flakes that fly off from zinc burning in the bed of glowing charcoal, and also to that floury powder left on the sheet of paper by the brilliant magnesium flame. In a word, lime is an oxid. "It is true that in producing this oxid the hand of man played no part, the combustion having taken place of itself, perhaps at the very beginning of things; and, since the creation of the world, the metallic part of lime has never been found alone anywhere in nature. It abounds nearly everywhere, but so greatly changed, so completely disguised in the combinations of which it forms a part, that it has required much shrewdness on the part of science to guess its existence, and still greater skill to restore some particles of it to their primitive [156] state, that of a real metal. Here is a pinch of burnt magnesium, and here one of powdered lime; look at them well and tell me, if you can, in what the two differ."

"We can't see any difference," the boys agreed, after a careful examination. "Both are white, and both look like flour."

"I see no difference, either," their uncle rejoined. "We are all three of one mind as to this close resemblance, though we know the two to be different substances. Let us, then, say, with those who are wiser than we, that this powder, lime, is the oxid of a metal, just as this other powder is the oxid of another metal, magnesium."

"What is this lime metal called?" asked Jules.

"It is called calcium."

"Why, that is n't so very different from what the farmers round here call lime; they call it cals."

"I will tell you, my boy, that the common speech of our part of the country, like that of other southern provinces, contains the relics of a tongue spoken long ago, venerable relics that, instead of being ridiculed as they are by the foolish, should be preserved with veneration. Our popular terms reproduce, though corrupted by centuries of use, the superb Latin tongue that came from Rome with civilization. In that language lime was called calx, and this word has been preserved almost unchanged in the common term you just named. So, you see, the rustic term needs no apology, its parentage being one of the noblest. He who speaks the native tongue of the South speaks something very like [157] Latin. Men of learning, who delight, not without reason, in going back to ancient usages, have made calx  into calcium, a sonorous and pleasing term, to designate the metal that enters into the formation of lime; but they might just as well have started with our popular word, cals.

"Well, then, the metal element in lime is calcium, the name coming from the Latin word calx, which means lime."

"Will you show us some of this metal?" asked Jules, eagerly.

"Alas, no, my lad! Our humble laboratory cannot afford so costly a curiosity. Not that calcium is rare, for it is to be found almost everywhere, the very rocks in many regions abounding in it, and whole mountain chains being largely made of it; but the difficulty is to extract it from the compounds that contain it, to bring it back to its original state of a simple metal. If we were to ransack all the chemical laboratories in France, we should perhaps find not more than a handful or two, so difficult and expensive is its preparation. That is why your Uncle Paul's collection of chemicals is now and always will be destitute of such treasures. But, at any rate, I can tell you about it. Imagine something white and shiny, almost like silver in appearance, and as soft as wax, so that it can be kneaded and molded with the fingers. That is calcium."

Here Emile interrupted his uncle. "What!" he cried, "calcium a metal that can be kneaded with the fingers like a piece of soft wax or a lump of clay?"

[158] "Yes, my child, this curious metal is soft enough to yield to the pressure of the fingers and be molded at will."

"I wish I had some to make into little men that would look like silver statues.

"It would be a very expensive amusement, and I have told you why. Also, it would be hard on your hands, for this terrible stuff catches fire more easily than anything you have ever seen. If, while you were molding it, your little statue were all at once to burst into flames, what would become of the sculptor?"

"That would n't be so much fun, would it?"

"Beware, then, of burns! Calcium catches fire by merely touching water. Burning coal, sulphur, and phosphorus are extinguished by water; calcium, on the contrary, is set on fire by it. Let it get a little damp and, behold, it begins to burn. Do not look incredulous when I tell you this, for it is nothing but the exact truth. In a lesson soon to follow I will show you that water is not, as you think it to be, always effectual in putting out a fire; and who knows—perhaps—well, we will see whether my purse will allow it."

"What is your purse going to allow?"

"The purchase, it may be, of a metal that, like calcium, has the peculiarity of catching fire in water."

"There are others, then?"

"Yes, three or four."

"And will you really show us one of them?"

"I make no promise. I will see, I will do my [159] best, if you continue to take as much pleasure in these studies as you have taken so far."

"We should be hard to please if we did n't like to see magnesium burn, phosphorus and zinc turn to snow, and other metals catch fire in water."

"To return to Emile's wish, calcium's readiness to take fire on touching water being now known to you, you see how dangerous it would be to mold it in your fingers, damp as these always are with their natural moisture. If we had any calcium, it is not a thing to hold in the hands and knead with the fingers; it is a dangerous substance to be left quietly reposing in its bottle.

"But now let us pass on from calcium to its oxid, lime. We find that this has a taste of its own, which the oxid of iron, zinc, and magnesium have not; and this taste is strong, disagreeable, and of a burning nature. The taste of phosphorus, after combustion, is sour, acid, whereas that of burnt calcium is caustic or fiery. Furthermore, it is not the sense of taste alone that lime affects unpleasantly; it exerts its corrosive energy on every part of the body. Handled carelessly for any length of time, it would gnaw the hands. Like the metal it comes from, it is a harsh substance, and prolonged contact with it is to be avoided.

"Not lacking in flavor, lime ought to be soluble in water; and in fact it is, though not to any great extent, but merely enough to give the water an unbearable taste. If we dilute in water a little lime previously reduced to a paste, the liquid will turn white like milk; then, after it has stood a while, the [160] undissolved lime will settle to the bottom and the water will resume its former clearness; but in this clear water, this water showing no trace of any foreign substance, there is dissolved lime, just as there is dissolved sugar in sweetened water. This we know from the burning, lime-like taste of the liquid."

Illustrating by experiment while he talked, Uncle Paul made his hearers taste of the water in which he had dissolved a little lime. A drop of the liquid on the tip of the finger and touched to the tongue was enough to convince them of its disagreeable taste. Emile made a grimace of disgust, spitting several times and rather overdoing his show of repugnance, for the flavor is not so offensive as his actions indicated. Uncle Paul then continued:

"Here are some violets that I picked just now in the garden. I showed you how these flowers and others of the same color lose their blue and turn red when acted upon by a burnt metalloid, an acid, notably phosphoric acid, which you have experimented with to the nearly complete devastation of the garden, so far as its blue flowers are concerned. Now, what will happen to violets when acted upon by a burnt metal, an oxid? That is what this lime here is going to show us."

Uncle Paul selected a violet and pressed it lightly between his fingers with a little moistened lime, whereupon the flower instantly turned a brilliant green.

"Chemistry seems to be a dye factory," observed Emile, astonished at this new transformation. [161] "You took a little acid and made the blue of the violet turn red, and now you take lime and make the same blue turn green. When I know enough about chemistry I'm going to make no end of colors for painting my pictures."

"You will be able to make as many as you please, for chemistry teaches, among other things, how from a colorless substance a bright color may be obtained by certain combinations of elements; and it also teaches how a colored substance may be made to lose its color or change it into such and such another color. Yes, the making of dyes is an important part of chemistry's work, and as the opportunity now occurs to give you some acquaintance with this interesting subject, I am glad to make the most of it. By using an acid we change the blue of the violet to red, and by using lime we change it to green. These two transformations, so complete and so instantaneous, give you an idea of how chemistry, with all the various drugs at is disposal, can produce the many different colors used by the painter and the dyer.

"I again take up my violet, turned green by the action of the lime, and dip it into this glass of water containing a few drops of some acid or other, no matter what, though in this instance it happens to be the acid that results from burning sulphur and is called sulphuric acid. We shall get better acquainted with it later. I could make phosphoric acid serve equally well if you had not used up our supply in your experiments with flowers. Now keep your eyes open for what happens. In the [162] liquid acid the violet turns red, just as it would have done had it not been first subjected to the action of lime. When it is changed to red, I take it out of the glass and place it a second time in contact with lime, whereupon it turns green again. If it were dipped into the acid once more, it would turn red, and then if touched with moist lime a third time it would again change to green. Thus the flower would continue to turn alternately green and red from being alternately subjected to the action of lime and of acid."

"Could these changes from green to red and from red to green go on a good many times?" asked Emile.

"As many times as you pleased. On coming out of the acid the violet would be red, and after touching moist lime it would be green. Oxids of iron, zinc, and magnesium do not have this property of turning violets and other blue flowers green, whereas the oxid of calcium, or lime, does. Whence comes this difference in the properties of these various metals? It comes from the same cause that determines the presence or the absence of taste. Lime, which dissolves in water, acts on the organs of taste, and it also acts on blue flowers by turning them green. The other three oxids, those of iron, zinc, and magnesium, do not dissolve in water, are tasteless, and do not turn blue flowers green, but leave them unchanged.

"But if these oxids were soluble in water, it is probable that they would have a burning taste, more or less like that of lime, and would turn violets and [163] other blue flowers green. Indeed, we know that, besides lime, some other oxids are soluble in water, and all these oxids without exception have the burning taste of lime, but much more pronounced; also, they all turn blue flowers green. Taking for the present no account of any but the soluble compounds, we may sum up in a few words what we have learned about acids and oxids.

"An acid, which is a metalloid combined with oxygen, has a sour taste, and turns blue flowers red. An oxid, which is a metal combined with oxygen, has a burning taste, and turns blue flowers green.

"I must now tell you that an acid and an oxid can combine and thus produce a compound substance, whose properties are, of course, different from those of either the acid or the oxid. You have not forgotten, I trust, that after chemical combination has taken place one must not expect to find in the resulting compound the same properties that were in the separate substances before they united. You have a fairly good notion of phosphoric acid, having seen it made by burning phosphorus and having ascertained its unbearable sourness by tasting it. Lime, a very common substance, is still better known to you, and its burning taste is even at this moment on the tip of your tongue. Now, you would never guess what happens when we combine these two, this acid and this oxid, both of them harmful substances that must needs inspire us with grave mistrust. They are changed into something of the most harmless nature imaginable,—into something, indeed, that is most neces- [164] sary in the animal body: they become the rigid material that gives strength to our bones.

"Throw the bone from a leg of mutton or from a mutton chop into the fire, and you will see it burn; but what takes fire in this fashion is the grease and other animal matter that impregnate the bone. When this flame has subsided, the bone will be found in its original shape, pure white, and so fragile as to crush under the pressure of your fingers. There we have the essential elements that go to make bone, and they are alone by themselves, purged by fire so as to contain no alien matter. Being incombustible, they have undergone no change by heart, whereas all else has been consumed.

"Now, chemistry tells us that this white, stony material to which the burnt bone has been reduced is formed—not entirely, but nearly so—of phosphoric acid and lime in combination. Grind this hard, white substance to a powder and taste it, and you will find it has no taste, whether sour or caustic. It is as if the substance contained neither phosphoric acid nor lime. It has no effect on either violets or any other blue flowers, their natural color remaining unchanged and without the slightest trace of red or green. In short, the properties of both acid and oxid have disappeared; what was active has become inert, and what was salt and what was caustic no longer have any taste. This stony material of bones, a combination of phosphoric acid and lime, is called phosphate of lime. It contains three elements, phosphorus, calcium, and oxygen, and therefore is, as we say, a ternary  compound.

[165] "There are innumerable similar compounds,—compounds, that is, made by combining an acid with an oxid. Chemistry calls them salts. Thus, the white, stone-like substance left after a bone is burned, and known as phosphate of lime, is a salt."

"You call that salt, that bone powder that has no salt taste at all?" exclaimed the boys, surprised to hear thus used a word they thought they knew the meaning of.

"Notice my young friends," their uncle corrected them, "I do not say the hard substance of the bone is salt; I say it is a  salt. In common language the word 'salt' is used as the name of what we add to our food to heighten its flavor, as when we salt our soup or fish; but chemistry gives to this term a much wider meaning, applying it to every compound resulting from the union of an acid with an oxid. Every acid— and the number of acids is large—can combine with one or another of the oxids, which are still more numerous, and thus are formed salts in great number. Kitchen or common salt has given us a general name which we apply to a great many other compounds; but it is an unfortunate misnomer in its common use, for our ordinary salt really does not belong in the class of salts as I have just defined them, not being composed of an acid and an oxid. Let us, then, disregard the salt we all know so well, let us forget its so-called salt taste and its household use, and henceforth let us understand by salt in chemical language any compound of an acid and an oxid, no matter what its taste, color, or appearance may be.

[166] "All these particulars, as a matter of fact, vary a good deal in the different salts. There are numerous salts that resemble kitchen salt in appearance, being colorless, vitreous (or glass-like), and soluble in water; and from this superficial resemblance to common salt they get their general name. Others are blue, containing oxid of copper; and others green, containing oxid of iron; while others still are yellow, reddish, or violet. In fact, we may find among them almost any color, but not one of these true salts has the peculiar taste of our kitchen salt. Some are bitter, some sour, some caustic, and some of an indescribable taste, but nearly all are intensely disagreeable. There are many, too, that will not dissolve in water, and so are tasteless; such is the hard material of which bones are chiefly made, and such, also, the freestone used for building. To this list we may add the plaster of Paris used in the ceilings of our rooms. Here, then, are three things—the mineral substance of bones, freestone, and plaster of Paris—that you certainly did not suspect of being salts."

"I had no idea of it," replied Emile. "If houses are built of salts such as freestone and plaster, I see that from a chemical standpoint the salt in sausage and ham must be something very different."

"Yes, very different indeed, for what chemists call a salt is to be found in almost any stone on the road, rock on the mountain, or handful of earth in the field."

"Then there must be quantities and quantities of those compounds of acid and oxid."

[167] "Yes, some are very abundant, forming the greater part as they do of rocks and stones and other minerals. The salt called carbonate of lime is one of them. Freestone, rubble-stone, limestone, from which we get lime, and also marble and many other kinds of stone are composed chiefly of carbonate of lime."

"And what is plaster of Paris called in chemistry?"

"Sulphate of lime. But these words mean nothing to you, and so we must stop here and have a little lesson in chemical grammar."

"Does chemistry have a grammar?"

"It has a language of its own, and therefore it has rules for correct speaking when referring to the things it has to do with. But Emile has no need to be frightened at this word 'grammar'; it has nothing to do with his hated conjugations. A few simple rules will make us master of it. Let us begin with the name of the acids. We know that an acid is a burnt metalloid, or, in more precise terms, a metalloid combined with oxygen. That of phosphorus is called phosphoric acid, and this example gives us our rule: to the name of the metalloid, or to the chief part of that name, is added the ending ic, and we have the name of the acid. Surely, there's nothing hard about that. Phosphorus  and ic, with the omission of us  to make a pleasanter sound, unite and give us phosphoric, and that's all there is to it; we have the name of the acid of phosphorus.

"Let us take another metalloid. You are ac- [168] quainted with nitrogen. I told you of its unwillingness to combine with oxygen. Nevertheless, by using skill and ingenuity enough, we may overcome this unwillingness and make the two elements unite. What will the acid thus formed be called?"

"According to the rule, I should say nitric acid," answered Emile. "Is that right?"

"Perfectly. Another metalloid is called chlorin, which you know nothing about as yet; but no matter, you can give the name of its acid."

"It must be chloric acid, or I am much mistaken."

"You are not in the least mistaken. Chloric acid is the correct name."

"That's easy enough. Oh, I wish our grammar at school—"

"Never mind your grammar at school just now, but let us proceed with our grammar of chemistry. From carbon we get an acid that you can name by following the rule already given."

"Carbon  and the ending ic  make carbonic," volunteered Jules. "It must be carbonic acid."

"In the same way you will be able to name the acid derived from sulphur."

"Oh, I have it!" cried Emile. "It is sulphuric acid."

"Yes, that is right. But enough, now, on the naming of acids. Let us pass on to that of oxids, which is simpler still. We say oxid of iron, oxid of zinc, oxid of copper, and so on, according to the metal in the compound we wish to name. I need only tell you to notice that certain oxids have retained their common name; familiar to people in [169] general from time immemorial, they have kept in chemistry the name acquired by long use. Thus, oxid of calcium is simply lime, both to the chemist and to the mason. The learned term gives way to the popular one. As we go on we shall meet with other oxids of the same exceptional sort in respect to name.

"There still remain to be considered in this connection the salts. They are formed, as we have already seen, by combining an acid and an oxid; and the rule to be followed in naming them is simple enough. In the name of the acid replace the ending ic  by ate, follow it with the name of the metal supplying the oxid, and you will have the term denoting the salt. Thus nitric acid and oxid of zinc form a salt called nitrate of zinc; carbonic acid and oxid of lead form another called carbonate of lead."

"I see," said Emile; "and so, phosphoric acid and oxid of zinc would make the salt called phosphorate of zinc."

"According to the rule that is quite right, but not right according to usage. The ear is hard to please, even that of a chemist, who, without boggling over the trifles of language, nevertheless finds phosphorate  a little disagreeable; and so for the sake of euphony the word is shortened to phosphate, as phosphate of zinc, phosphate of copper, etc. In the same way sulphurate  is shortened to sulphate, as sulphate of iron, sulphate of lead, and so on.

"One word more and we shall have done with the subject. When a salt contains an oxid that has [170] kept its common name instead of the name of the metal, this common name is still retained. Take as an illustration the salts whose oxid is furnished by calcium. We do not say sulphate of calcium, carbonate of calcium, but sulphur of lime, whish is plaster of Paris, and carbonate of lime, which is limestone. Herewith ends our grammar."

"The whole of it?"

"Not the whole, but the most important part."

"Oh, I wish our school grammar—"

"Tush! Don't worry about that."


 Table of Contents  |  Index  | Previous: Burning Metals  |  Next: A Talk on Tools
Copyright (c) 2000-2017 Yesterday's Classics, LLC. All Rights Reserved.