Metals.
We have a few words to say about a class of bodies called metals, which are of the utmost importance to mankind, and indeed without some of them, especially iron, few of the arts of civilized life could exist.
Fifty substances are now included in the list of metals; some of them, however, are only supposed to exist, such as ammonium, the supposed base of ammonia; and very many are to be viewed rather in the light of chemical curiosities, as from their great rarity they are too expensive for use, even if possessed of valuable properties of which others might be destitute.
Several metals have been known from the earliest period of which we have any record; such were iron, gold, silver, copper, lead, tin, mercury, and probably zinc, or at least its ores; for brass, which is an alloy of copper and zinc, is frequently mentioned in the early part of the Old Testament. In the sixteenth century others were discovered, such as antimony and bismuth. In the last century, cobalt, arsenic, platinum, nickel, manganese and chromium, together with several unimportant metals, were discovered by various philosophers; while in the present century, Dr. Wollaston discovered rhodium, the hardest and nearly the most indestructible of all the metals; and a few years later Sir Humphry Davy found that the alkalies, potash and soda, with many of the earths as they were called, had each a metal for its base, to which he gave the Latin name of the alkali or earth, with the termination um, as potassium, the base of potassa, sodium of soda, calcium of calx (lime), etc.
Until Sir H. Davy’s discovery of the metals of the alkalies, great specific gravity was regarded as one of the most striking characteristics of a metal, the lightest of them being much heavier than the heaviest earth; but potassium is very much lighter than water, and not much heavier than spirits of wine. The other metals vary from a specific gravity of nearly twenty-one—or twenty-one times heavier than an equal bulk of water—that of platinum, to somewhat less than seven, which is the specific gravity of antimony.
When pure, they all have a luster, differing indeed among themselves, but so peculiar that it is called the metallic luster; for instance, gold and copper are yellow and red—nearly all the others white, but of a different shade; still there is no mistaking their metallic character, no other substances at all equaling them in this respect. They are also opaque, although some, like gold, when reduced to thin films, allow light to pass through them. They are all good conductors of heat and electricity, though some possess that property to a greater extent than others.
Many of them are what is called malleable, that is, may be extended or spread out by rolling, or beating them with a hammer; and ductile, or have the property of being drawn out into wire. Gold, silver, copper, and iron are the most remarkable in this respect.
All the metals are fusible, but some require very different degrees of heat to render them fluid—platinum requiring the heat of the oxy-hydrogen blowpipe, while tin melts in the flame of a candle, and mercury is fluid at all temperatures in this climate, but becomes solid at 40 degrees Fahrenheit below 0—a temperature occasionally experienced in the Arctic regions, where the mercurial thermometer is useless, the mercury becoming solid.
They are all excellent conductors of heat and electricity, and have the property of reflecting light and forming mirrors; for looking-glasses owe their power of reflecting objects principally to what is called the “silvering;” that is, a mixture of mercury and tin spread over the back of the glass, which being transparent, allows the image reflected from the metal to pass through it.
The following classification is most instructive, because it suggests to the young student that there must be identical properties in the metals thus placed together:
Class 1. Ammonium, cæsium, lithium, potassium, sodium.
Class 2. Calcium, barium, strontium.
Class 3. Aluminium, cerium, didymium, erbium, glucinium, lanthanum, thorium, yttrium, zirconium.
Class 4. Zinc class: cadmium, magnesium, zinc.
Class 5. Iron class: cobalt, chromium, indium, iron, manganese, nickel, uranium.
Class 6. Tin class: niobium, tantalum, tin, titanium.
Class 7. Tungsten class: molybdenum, tungsten, vanadium.
Class 8. Arsenic class: antimony, arsenic, bismuth.
Class 9. Lead class: lead, thallium.
Class 10. Silver class: copper, mercury, silver.
Class 11. Gold class: gold, iridium, osmium, palladium, platinum, rhodium, ruthenium.
Potassium.
Potassium was discovered by Sir H. Davy in the beginning of the present century. It is a brilliant white metal, so soft as to be easily cut with a penknife, and so light as to swim upon water, on which it acts with great energy, uniting with the oxygen, and liberating the hydrogen, which takes fire as it escapes.
Experiment.
Trace some continuous lines on paper with a camel’s-hair brush dipped in water, and place a piece of potassium about the size of a pea on one of the lines, and it will follow the course of the pencil, taking fire as it runs, and burning with a purplish light. The paper will be found covered with a solution of ordinary potash. If turmeric paper be used, the course of the potassium will be marked with a deep brown color.—Corollary. Hence, if you touch potassium with wet fingers you will burn them.
If a small piece of the metal be placed on a piece of ice, it will instantly take fire, and form a deep hole, which will be found to contain a solution of potash.
In consequence of its great affinity for oxygen, potassium must be kept in some fluid destitute of that element, such as naphtha.
Caution!—As the globules of potassium after conversion into potash, when thrown on ice or water burst, strewing small particles of caustic hot potash in every direction, the greatest care should be taken to keep at a sufficient distance whilst performing the above experiment.
Saltpeter, or niter, is a compound of this metal (or rather its oxide) with nitric acid. It is one of the ingredients of gunpowder, and has the property of quickening the combustion of all combustible bodies.
Mix some chlorate of potash with lump sugar, both being powdered, and drop on the mixture a little strong sulphuric acid, and it will instantly burst into flame. This experiment also requires caution.
Want of space precludes us from considering the individual metals and their compounds in detail; it must suffice to describe some experiments showing some of their properties.
The different affinities of the metals for oxygen may be exhibited in various ways. The silver or zinc tree has already been described.
Experiments.
1. Into a solution of nitrate of silver in distilled water immerse a clean plate or slip of copper. The solution, which was colorless, will soon begin to assume a greenish tint, and the piece of copper will be covered with a coating of a light gray color, which is the silver formerly united to the nitric acid, which has been displaced by the greater affinity or liking of the oxygen and acid for the copper.
2. When the copper is no longer coated, but remains clean and bright when immersed in the fluid, all the silver has been deposited, and the glass now contains a solution of copper.
Place a piece of clean iron in the solution, and it will almost instantly be coated with a film of copper, and this will continue until the whole of that metal is removed, and its place filled by an equivalent quantity of iron, so that the nitrate of iron is found in the liquid. The oxygen and nitric acid remain unaltered in quantity or quality during these changes, being merely transferred from one metal to another.
A piece of zinc will displace the iron in like manner, leaving a solution of nitrate of zinc.
Nearly all the colors used in the arts are produced by metals and their combinations; indeed, one is named chromium, from a Greek word signifying color, on account of the beautiful tints obtained from its various combinations with oxygen and the other metals. All the various tints of green, orange, yellow, and red, are obtained from this metal.
Solutions of most of the metallic salts give precipitates with solutions of alkalies and their salts, as well as with many other substances, such as what are usually called prussiate of potash, hydro-sulphuret of ammonia, etc.; and the colors differ according to the metal employed, and so small a quantity is required to produce the color that the solutions before mixing may be nearly colorless.
Experiments.
1. To a solution of sulphate of iron add a drop or two of a solution of prussiate of potash, and a blue color will be produced.
2. Substitute sulphate of copper for iron, and the color will be a rich brown.
3. Another blue, of quite a different tint, may be produced by letting a few drops or a solution of ammonia fall into one of sulphate of copper—a precipitate of a light blue falls down, which is dissolved by an additional quantity of the ammonia, and forms a transparent solution of the most splendid rich blue color.
4. Into a solution of sulphate of iron let fall a few drops of a strong infusion of galls, and the color will become a bluish-black—in fact, ink. A little tea will answer as well as the infusion of galls. This is the reason why certain stuffs formerly in general use for dressing-gowns for gentlemen were so objectionable; for as they were indebted to a salt of iron for their color, buff as it was called, a drop of tea accidentally spilt produced all the effect of a drop of ink.
5. Put into a largish test tube two or three small pieces of granulated zinc, fill it about one-third full of water, put in a few grains of iodine and boil the water, which will at first acquire a dark purple color, gradually fading as the iodine combines with the zinc. Add a little more iodine from time to time, until the zinc is nearly all dissolved. If a few drops of this solution be added to an equally colorless solution of corrosive sublimate (a salt of mercury) a precipitate will take place of a splendid scarlet color, brighter if possible than vermilion, which is also a preparation of mercury.
Crystallization of Metals.
Some of the metals assume certain definite forms in returning from the fluid to the solid state. Bismuth shows this property more readily than most others.
Experiment.
Melt a pound or two of bismuth in an iron ladle over the fire; remove it as soon as the whole is fluid; and when the surface has become solid break a hole in it, and pour out the still fluid metal from the interior; what remains will exhibit beautifully-formed crystals of a cubic shape.
Sulphur may be crystallized in the same manner, but its fumes, when heated, are so very unpleasant that few would wish to encounter them.
One of the most remarkable facts in chemistry, a science abounding in wonders, is the circumstance, that the mere contact of hydrogen, the lightest body known, with the metal platinum, the heaviest, when in a state of minute division, called spongy platinum, produces an intense heat, sufficient to inflame the hydrogen; of course this experiment must be made in the presence of atmospheric air or oxygen.
Time and space (or rather the want of them) compel us to conclude with a few experiments of a miscellaneous character.
To Form a Solid From Two Liquids.
Prepare separately, saturated solutions of sulphate of magnesia (Epsom salts) and carbonate of potash. On mixing them the result will be nearly solid.
Solutions of muriate of lime and carbonate of potash will answer as well.
To Form a Liquid From Two Solids.
Rub together in a Wedgewood mortar a small quantity of sulphate of soda and acetate of lead, and as they mix they will become liquid.
Carbonate of ammonia and sulphate of copper, previously reduced to powder separately, will also, when mixed, become liquid, and acquire a most splendid blue color.
The greater number of salts have a tendency to assume regular forms, or become crystallized, when passing from the fluid to the solid state; and the size and regularity of the crystals depend in a great measure on the slow or rapid escape of the fluid in which they were dissolved. Sugar is a capital example of this property; the ordinary loaf-sugar being rapidly boiled down, as it is called: while to make sugar-candy, which is nothing but sugar in a crystallized form, the solution is allowed to evaporate slowly, and as it cools it forms into those beautiful crystals termed sugar-candy. The threads found in the center of some of the crystals are merely placed for the purpose of hastening the formation of the crystals.
Experiments.
1. Make a strong solution of alum, or of sulphate of copper, or blue vitriol, and place in them rough and irregular pieces of clinker from stoves, or wire-baskets, and set them by in a cool place, where they will be free from dust, and in a few days crystals of the several salts will deposit themselves on the baskets, etc.; they should then be taken out of the solutions, and dried, when they form very pretty ornaments for a room.
2. Fill a Florence flask up to the neck with a strong solution of sulphate of soda, or Glauber’s salt, boil it, and tie the mouth over with a piece of moistened bladder while boiling, and set it by in a place where it cannot be disturbed. After twenty-four hours it will probably still remain fluid. Pierce the bladder covering with a penknife, and the entrance of the air will cause the whole mass instantly to crystallize, and the flask will become quite warm from the latent caloric, of which we have spoken before, given out by the salt in passing from the fluid to the solid state. It is better to prepare two or three flasks at the same time, to provide against accidents, for the least shake will often cause crystallization to take place before the proper time.
Changes of Color Produced by Colorless Liquids.
Make a strong infusion of the leaves of the red cabbage, which will be of a beautiful blue color; drop into it a few drops of dilute sulphuric acid, and the color will change to a bright red; add some solution of carbonate of potash, or soda, and the red color will gradually give way to the original blue; continue adding the alkaline solution, and the fluid will assume a bright green color. Now resume the acid, and as it is dropped in, the color will again change from green to blue, and from blue to red. Now this simple experiment illustrates three points: first, that acids change the color of most vegetable blues and greens to red; second, that alkalies change most blues and reds to green; and third, that when the acid and alkali are united together, they both lose their property of changing color, and become what is called a neutral salt, i.e. a compound possessing the properties of neither of its constituents.