Chapter XXIV: Part III: Scientific Pursuits (2)

A lighted taper plunged into this gas is instantly extinguished. It is very dangerous to animal life if respired. It has the property of destroying animal effluvia, and was once employed to purify the cathedral of Dijon, which was so filled with putrid emanations from the bodies buried in it, that it had been closed for some time. It perfectly succeeded, but it is so destructive to all metallic substances that it is not used now, for the chlorides of lime and zinc have since been discovered to act more effectually than the muriatic acid gas, without its inconvenience.

The compounds of hydrogen with iodine are passed over.

With nitrogen, hydrogen unites and forms one of the most extraordinary compounds in the whole range of chemistry,--the gas called ammonia. This is the only gas possessing what are called alkaline properties; _i. e._ it changes the blue colour of certain vegetables to green, yellow to deep brown, and unites with the acids to form neutral compounds, just as the other alkalies, potash and soda, which are oxides of metals. It may be procured in abundance by heating the hydrochlorate of ammonia, or sal ammoniac, as it is usually called, with quick-lime, which takes the hydrochloric acid, and sets free this remarkable gas. It must be received over mercury, as it is absorbed to almost any extent by water, forming the fluid sold as “spirits of hartshorn” in the shops.

This gas is colourless and transparent, lighter than atmospheric air, and will not support combustion; it has a very pungent but not disagreeable smell. Under certain circumstances it is combustible.

EXPERIMENTS.

1. Take a bottle containing chlorine gas, and invert over its mouth another filled with ammoniacal gas; then if the bottles be held in the hand (guarded by a pair of gloves), and suddenly turned, so that the chlorine be uppermost, the two gases will unite so rapidly that a white flame fills the bottles for an instant.

2. Substitute for the chlorine of the last experiment a bottle of carbonic or hydrochloric acid gas; in either case the gases disappear, and a light white powder settles on the sides of the bottles, being the carbonate or hydrochlorate of ammonia, according to the acid used.

Carbonate of ammonia is the substance sold for “smelling salts;” and the hydrochlorate, or muriate of ammonia, is the salt called “sal ammoniac,” whence the alkaline gas was first obtained, and from which it got its name of ammonia. The salt itself was so called, because it was formerly brought from the deserts near the ruins of the temple of Jupiter Ammon.

This salt is, as has been shown, a compound of muriatic acid gas and ammoniacal gas, containing therefore only _three_ simple elements--hydrogen, chlorine, and nitrogen, all gases, and known only in the gaseous state, its symbol being NH₄Cl; yet they by union form a solid body, resembling in all essential qualities the salts of potash and soda, which are oxides of known metals. Moreover, if some mercury be placed in a solution of this salt, and subjected to the action of galvanism, the _negative_ pole being applied to the mercury, and the positive to the sal ammoniac, the mercury presently loses its fluidity, increases greatly in size, and in fact presents the same appearance as when it is mixed with some metal, forming what is called an “amalgam.” When the battery ceases to act, a succession of white films forms on the surface of the amalgam, and the mercury soon returns to its original state. How is this to be explained? Some chemists have supposed that there must be a _base_ united to the mercury, and have named this hypothetical substance “ammonium,” to correspond to potassium and sodium, the bases of potash and soda, which resemble ammonia in so many properties. But what is this ammonium? and how is it formed? for hydrogen and nitrogen are simple elementary bodies. Are _all_ metals compounds of gases? and are there but a few elements instead of the 64 now enumerated? This, however, is a difficult question, not fitted for discussion here.

Carbonate of ammonia may be obtained by mixing together powdered chalk (which is a carbonate of lime) and muriate of ammonia, and heating the mixture in close vessels, when the salt in question will rise in fumes, and be condensed in a mass in the upper part of the vessel. It is, however, so largely produced in other manufactures, particularly in gas-works, that there is no necessity to resort to the more expensive and direct method. It is the well-known “smelling salts.”

The only other salt of ammonia worth our notice here is the nitrate, from the destructive distillation of which is obtained the nitrous oxide, or laughing gas, already mentioned.

IODINE.

On the coasts of certain islands belonging to the Duke of Argyll, vast quantities of sea-weed are occasionally torn up from their ocean beds and deposited on the shores. This weed, after being partially dried by exposure to the sun and air, is burnt in a shallow pit; the ashes are then collected, and form the commercial raw material called kelp, from which iodine is procured by a gradual series of processes.

EXPERIMENTS.

Iodine has a beautiful metallic lustre, with a bluish black colour, and should be kept in a well-stoppered bottle. A small quantity placed in a clear flask and heated, affords a magnificent violet vapour, which may be poured from the flask into another glass vessel, when it condenses again into crystalline plates. The colour of the vapour originates the name of this element, so called from the Greek Ἰώδης, violet-coloured. If a little iodine be placed in contact with a thin slice of phosphorus, the latter takes fire almost immediately.

BROMINE.

So called from the Greek βρόμος, a bad odour, is most intimately allied with chlorine and iodine; like these elements it belongs to the sea, and is a constituent of sea-water. Bromine is a very heavy fluid, and should be preserved by keeping it covered with water in a stoppered-bottle.

Experiments with liquid bromine are not recommended, as all the most interesting ones can be performed with the vapour, which is easily procured by letting fall a few drops of bromine into a warm dry bottle.

EXPERIMENTS.

Pounded antimony sprinkled into the vapour takes fire immediately.

A thin slice of phosphorus placed in a deflagrating ladle and placed into the vapour of bromine ignites very quickly.

A solution of sulphate of indigo, or an infusion of red cabbage, are easily bleached by being shaken violently with the vapour of bromine.

FLUORINE.

In many parts of England, especially in Devonshire, Cornwall, and above all in Derbyshire, is found a very beautiful mineral, known by the name of Fluor Spar, Derbyshire Spar, and called by the miners Blue John, to distinguish it from another mineral found, in the same locality, called _Black Jack_. It occurs in very regular and frequently large crystals in the form of cubes, and occasionally in octoëdra. It is a compound of calcium with fluorine, and is very abundant in certain fossil bones. This element, in combination with hydrogen and called hydrofluoric acid, acts so energetically upon all substances containing silica, that it cannot be preserved in vessels of glass or porcelain--very few of the metals are capable of resisting its action, lead being nearly the only common metal possessed of this power. Gutta percha may also be employed for vessels to hold it.

This property of dissolving silica, has caused this acid to be used for engraving on glass.

EXPERIMENT.

Mix one part of powdered fluor-spar, quite pure, with two parts of oil of vitriol, in a saucer, and apply a gentle heat, when the acid will be disengaged in the form of vapour. Prepare a piece of glass after the manner of engraving on copper, by coating it with a thin covering of wax, placing a paper over the wax, and then drawing any design with a sharp-pointed instrument, when, on removing the paper, the wax-coating will be found to be removed wherever the instrument has passed over it. Now invert, this glass over the fumes of the acid for half an hour or so, and then heat the glass so as to soften the coating, and wipe it off; the design will then appear “bitten in” as the term is, that is, the acid will have dissolved the glass wherever it was not protected by the wax, and will exhibit the design indelibly fixed on the glass.

This acid requires the greatest care in handling, for it is extremely corrosive, producing very troublesome ulcers if it comes in contact with the skin; even the fumes will produce smarting if the skin is long exposed to them.

CARBON.

The next substance in our list of elementary bodies is named carbon.

The purest form of carbon is the precious stone called diamond, which consists entirely of carbon in a crystallized form. The French chemist Lavoisier was the first who proved the combustibility of the diamond; and Sir H. Davy found that when once set on fire it would continue to burn in oxygen gas air, and that the product of the combustion was carbonic acid gas, exactly equal in quantity to the gas produced by burning an equal weight of pure charcoal, the most common form of carbon.

Plumbago, or “black-lead,” as it is very improperly called, is also nearly pure carbon, a very small quantity of iron being united with it.

By far the greater part of all vegetable, and a very large portion of animal bodies consists of carbon; and in the state of carbonic acid in combination with lime and some other earths, it forms nearly the half of all the chalk, marble, and limestone of our hills; so that it is, in one shape or other, one of the most widely diffused bodies in nature.

Carbon forms two gaseous compounds with oxygen; the first, called carbonic oxide, is easily obtained by boiling oxalic acid with its own bulk of sulphuric acid, in a flask to which a cork and bent tube is attached. The gas comes over in large quantities, and must be collected in a gas jar, or the pneumatic trough. It is inflammable, and burns with a lambent blue flame.

The other compound, carbonic acid, is transparent, colourless, much heavier than atmospheric air, has an agreeable taste, has the power of irritating the mucous membrane of the nose, (as any one can tell who has drunk soda-water), without possessing any particular odour, is absorbed by water, does not support respiration, and extinguishes flame.

Carbonic acid gas may be obtained with the greatest facility by pouring some muriatic or sulphuric acid, diluted with about six parts of water, upon some pieces of marble or limestone in a bottle with a tube attached, when the gas comes over in torrents. It may be collected over water.

EXPERIMENTS.

1. To show the great comparative weight of this gas, place a lighted taper at the bottom of a tall glass jar, then take a jar full of carbonic acid gas, and pour it as you would pour water into the jar containing the lighted taper; you will soon find the taper will be extinguished as effectually as if you had poured water on it, and the smoke of the taper will float on the surface of the gas in very beautiful wavy forms.

2. Heat a piece of the metal potassium in a metal spoon (platinum is best), and if introduced in a state of ignition into the gas, it will continue burning brilliantly, producing a quantity of dense smoke, which is the carbon from the carbonic acid, the potassium having seized the oxygen and being converted by it into potash.

3. If a mouse, bird, or other small animal, be placed in a jar of this gas, it becomes insensible almost immediately, but if speedily removed it will occasionally recover.

4. Shake up some water with some of this gas in a bottle; the greater part of the gas will be absorbed by the water, which acquires a sparkling appearance and a pleasant sharp taste; with the addition of a little soda this becomes the well-known beverage called soda-water, so famous for removing the morning headaches caused by “_that salmon_” having disagreed at yesterday’s dinner.

It is the presence of this gas which renders it so dangerous to descend into deep wells, for by its great weight it collects at the bottom, and instantly suffocates any unfortunate person who incautiously subjects himself to it. Hence it is prudent always to let down a lighted candle before any one descends into a well, or other deep excavation, and if the candle is extinguished, it is necessary to throw down several pails of water, lime-water if possible, and again to try the candle, which must burn freely before it is safe for any one to descend.

It is this same gas under the name of “choke-damp,” which proves so dangerous to miners, particularly after an explosion of “fire-damp,” for it is the principal product of the explosion, and it is by no means an easy matter to dislodge it.

Carbonic acid gas has been condensed into the fluid form by causing it to be disengaged under great pressure; the fluid acid has the appearance of water. When the pressure is removed, as by allowing some of the fluid acid to escape from the vessel in which it has been condensed, it instantly reassumes the gaseous form, and in so doing absorbs so much latent caloric that a portion of the acid is actually solidified, and appears in the shape of _snow_, which may be collected and preserved for a short time. After a lecture by Mr. Addams before the Ashmolean Society of Oxford, I carried a kind of _snowball_ of carbonic acid for a distance of 500 or 600 yards, and placed it in a saucer in a room. It evaporated very rapidly, and left no residue, not even a mark where it had lain. It was too _cold_ to be touched by the naked hand without pain.

Carbonic acid and lime are mutually tests for each other. If a jar containing a little lime-water be put into a jar of this gas, it speedily becomes turbid, the gas uniting with the lime, and producing chalk (the carbonate of lime), which is insoluble in water.

This gas is produced in large quantities by the respiration of animals, as may be proved by respiring through a tube immersed in lime-water, when the water will be instantly rendered turbid from the formation of chalk.

CARBON AND HYDROGEN.

To the combination of these elements in various proportions, and with the occasional addition of other substances, we are indebted for all, or nearly all, our means of obtaining light and heat. Coal, wood, spirit, oil, and all the varieties of fats, are composed principally of carbon and hydrogen, and may easily be converted into the gas with which our houses and streets are lighted, which is nearly pure carburetted hydrogen.

The two chief definite gaseous compounds of these two elements are the light carburetted hydrogen, and the heavy carburetted hydrogen, or olefiant gas. The first is easily procured by stirring the bottom of stagnant water on a hot summer’s day, and collecting the bubbles in a bottle filled with water and inverted over the place where the bubbles rise. This gas burns with a yellowish flame, and when mixed with a certain proportion of air, or oxygen gas, explodes with great violence on the application of a flame. It is the much dreaded fire-damp generated so profusely in some coal-mines, and causing such fearful destruction to life and property when accidentally inflamed.

The other compound, the heavy carburetted hydrogen, forms part of the gas used for illumination; and, in fact, whatever substance is employed for artificial light, whether oil, tallow, wax, &c. &c. it is converted into this gas by heat, and then furnishes the light by its own combustion.

This gas has some very curious properties, and may be obtained nearly pure by mixing in a retort, _very carefully_, one part of spirits of wine and four of sulphuric acid. A lamp must be placed under the retort, when the gas will be speedily disengaged, and come over in great abundance; it may be collected over water.

This gas is transparent, colourless, will not support combustion, but is itself inflammable, burning with a brilliant white light, and being converted into carbonic acid and water. If mixed with three or four times its bulk of oxygen, or with common atmospheric air in much larger proportions, it explodes with great violence.

This gas is sometimes called “olefiant gas,” from the property it has of forming an oily substance when mixed with chlorine.

EXPERIMENT.

Into a jar standing over water half full of this gas, pass an equal quantity of chlorine gas. The gases will speedily unite and form an oily-looking liquid, which may be collected from the sides of the jar as it trickles down. By continually supplying the jar with the two gases as they combine, a considerable quantity of this substance may be collected. Care should be taken that the olefiant gas is rather in excess.

The substance produced is insoluble in water, with which it should be washed by shaking them together in a tube, and has a pleasant sweetish taste and aromatic smell, somewhat resembling ether.

COAL GAS.

The gas so universally employed for the purposes of illumination is a mixture of the carburetted and the bi-carburetted hydrogen, with minute portions of other gases scarcely worth mentioning. It is procured by submitting coals to a red heat in iron retorts, having a tube passing from one end, along which passes all the fluid and gaseous matter separated from the coal, namely, gas tar, ammoniacal liquor, and various gases, carburetted hydrogen, carbonic acid, sulphuretted hydrogen, &c. &c. The tar and ammoniacal liquor remain in the vessel in which the tubes from the retorts terminate, and the gaseous productions are conveyed through water and lime to separate the impurities; the remaining gas, now fit for use, passes into large iron vessels, called gasometers, inverted over water (like the jars in a pneumatic trough), whence it is sent through pipes and distributed where required. What remains in the retorts is called coke. It consists principally of charcoal, mixed with the earthy and metallic particles contained in the coal.

EXPERIMENT.

If you possess an iron bottle, fill it with powdered coal, and attach a flexible tube to it, and put it in the fire: as soon as it becomes red hot, large quantities of smoke will escape from the end of the tube, being the gas mixed with all its impurities. By passing it through water (if mixed with lime it will be better), the gas may be collected in jars standing over water, and submitted to experiment. If you do not possess a bottle, take a tobacco-pipe with a large bowl, (a “churchwarden” for example); fill the bowl with small coal, cover it with clay or putty, and when dry put it into the fire, and the gas will soon appear at the other end of the pipe, when it may be lighted, or the gas may be collected over water, as in the former experiment.

The light carburetted hydrogen contained in this gas is given off spontaneously in some coal-mines, and as it forms explosive mixtures with atmospheric air, the mines where it abounds could not be worked except at the greatest risk until about the beginning of the present century, when Sir H. Davy, while prosecuting some researches on the nature of flame, found that flame would not pass through metallic tubes, and he gradually reduced the length of the tubes, until he found fine iron wire gauze formed an effectual barrier against the passage of flame. He then thought that if the light in a lantern were surrounded with this gauze, it might safely be used in an inflammable atmosphere, where a naked light would instantly cause an explosion. Upon submitting the lamp to experiment, he found that by passing coal gas by degrees into a vessel in which one of his lamps was suspended, the flame first became much larger, and then was extinguished, the cylinder of gauze being filled with a pale flame, and though the gauze sometimes became red-hot, it did not ignite the gas outside. As the supply of coal gas was diminished, the wick of the lamp was rekindled, and all went on as at first. A coil of platinum wire was afterwards suspended in the lamps, which becomes intensely heated by the burning gas, and gives out sufficient light to enable the miner to see to work. As long as the gauze is perfect it is almost impossible for the external air to be kindled by the wick of the lamp, but the miners are so careless that they will often remove the gauze to get a better light, to look for a tool, or some cause equally trivial, and many lives have been lost in consequence of such carelessness.

The effect of fine wire gauze in preventing the passage of flame may be shown by bringing a piece of the gauze gradually over the flame of a spirit-lamp, until it nearly touches the wick, when the flame will be nearly extinguished, but the vapour of the spirit passes through, and may be lighted on the upper side of the gauze, which will thus have a flame on either side, though totally unconnected with each other. The flame from a gas-burner will answer as well as the spirit-lamp.

Nearly all the fluids, and solids also, used for procuring artificial light, such as naphtha, various oils, tallow, wax, spermaceti, spirits of wine, ether, &c. &c. are compounds of carbon and hydrogen in different proportions, with the occasional addition of some other elements, especially oxygen and hydrogen, in the proportions to form water; as a general rule, those bodies containing the greatest proportion of carbon give the most light, though not necessarily the most heat.

PHOSPHORUS.

The next body we have to notice is phosphorus, a most remarkable substance, procured from the earthy part of bones by a process not worth detailing here. It should be _always_ kept under water, and the naked fingers should not be allowed even to touch it, for the smallest piece getting under the nail will inflame the first time the hand comes near the fire, and produce a sore very painful and difficult to heal. It should be cut under water by a knife or scissors, and removed with a pair of forceps. Its combustible properties have been frequently mentioned. It has also the property of shining in the dark, so that if you write on a wall with a solution of phosphorus in oil, the letters will appear luminous in the dark--there is no danger, excepting from the greasiness of the oil.

Of the compounds of phosphorus with oxygen we have nothing to do here, but it forms with hydrogen a very curious gaseous compound, which takes fire spontaneously on the contact of air, or almost any gas containing oxygen.

EXPERIMENTS.

It may be procured in either of two ways, according to the purpose for which it is wanted. The simplest way is to put a lump or two of phosphuret of lime into a saucer, about two inches in depth, containing some very diluted hydrochloric acid; bubbles of gas will speedily arise, and bursting on the surface of the fluid will burn with a slight explosion, and a circular wreath of smoke will rise into the atmosphere, enlarging as it rises, and wreathing itself round and round in the most elegant forms. Care must be taken that the phosphuret is _fresh_, and has been kept in a well-closed bottle, or the experiment will fail. The apartment must be free from draughts. If you desire to collect the gas, another method must be employed.

Fill a small retort _quite full_, neck and all, of a solution of caustic potash, drop five or six pieces of phosphorus into it, place the finger on the end of the retort, and immerse it in a basin also containing a _hot_ solution of potash, remove the finger, and on applying the heat of a lamp to the retort, the gas will soon be disengaged rapidly, and drive out the fluid in the retort; it then escapes into the air, when it inflames with the same appearances as before described. Or it may be collected in gas jars filled with the potash solution, and held over the mouth of the retort. The object in using _hot_ solution of potash in the basin is, that when the gas ceases to be given off, and the heat of the lamp is withdrawn, the hot fluid may gradually fill the vacuum which will form in the retort, and so prevent its being broken.

This gas is transparent and invisible, like most other gases. It is very poisonous if inhaled. If kept for any time, it loses its property of spontaneous inflammation, and must therefore be made at the time it is required.

SULPHUR.

Sulphur, or brimstone, as it is frequently called, is sold in the form of sticks, or _roll_ brimstone, or in fine powder called flowers of brimstone.

It is capable of showing electric phenomena when rubbed, giving out slight sparks, and first attracting and then repelling light bodies, such as small pieces of paper, &c. It is so bad a conductor of heat, that if grasped suddenly in a hot hand, it will crack and split into pieces just as glass does when suddenly heated or cooled--of course I am speaking of the roll brimstone. Water has no effect on it, as may be seen in the pans placed for pet dogs to drink out of, where the same piece of brimstone lies for years entirely unaltered, though it is supposed to prevent the dogs from having the mange!

Sulphur is largely used in the arts, principally in the manufacture of gunpowder, and fireworks of various kinds.

It combines with hydrogen, and forms a gaseous compound called sulphuretted hydrogen, which is almost the most poisonous of all the gases. It fortunately has so abominable smell, that due notice is given of its presence. Rotten eggs, a dirty gun-barrel, cabbage water, putrid animal and vegetable matter, &c. are indebted to this gas for their inviting odour; and it is found in certain mineral springs, as at Harrogate, where the water contains a considerable quantity of this gas, and is found useful in many diseases of the skin. It is also given off in a gaseous form by some volcanoes.

This gas may be obtained by pouring dilute hydrochloric acid upon a metallic sulphuret, such as that called crude antimony, being a native sulphuret of that metal. The gas may be kept for a short time over water. It is colourless and transparent, inflammable, but quite irrespirable, a small bird dying instantly when placed in air containing only 1/1500th of this gas. Its most remarkable property perhaps is the effect it has on certain metallic oxides, and other metallic salts, blackening them instantly. White paint is easily stained by this gas, and it will darken the colour of a metal in a solution, especially of lead, even when diluted with 20,000 times its weight of water. By way of experiment, slips of riband, silk, or even paper, may be wetted with various metallic solutions, such as silver, mercury, lead, &c. or words may be written with the solutions, and on holding them over a stream of this gas they will be instantly darkened.

If this gas be collected in the pneumatic trough, which is usually painted _white_, you will have the pleasure of seeing the colour changed to a very dark brown, when your experiments are finished. With this very limited description of some of the non-metallic elements and their combinations, we must, for want of space, take leave of this division of chemistry; “the beginning of which is pleasure, its progress knowledge, its objects truth and utility.”--(_Davy._)

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 potassi_um_, the base of potassa, sodi_um_ of soda, calci_um_ of calx (lime), &c.

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 lustre, differing indeed among themselves, but so peculiar that it is called the metallic lustre, 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 equalling 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° Fahr. 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, while acting upon potash with the enormous galvanic battery of the Royal Institution, consisting of 2,000 pairs of 4-inch plates. 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 colour.--_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.

Saltpetre, or nitre, 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, page 357.

EXPERIMENTS.

1. Into a solution of nitrate of silver in distilled water immerse a clean plate or slip of copper. The solution, which was colourless, will soon begin to assume a greenish tint, and the piece of copper will be covered with a coating of a light grey colour, 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 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 colours used in the arts are produced by metals and their combinations; indeed, one is named _chromium_, from a Greek word signifying colour, 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, &c.; and the colours differ according to the metal employed, and so small a quantity is required to produce the colour that the solutions before mixing may be nearly colourless.

EXPERIMENTS.

1. To a solution of sulphate of iron add a drop or two of a solution of prussiate of potash, and a blue colour will be produced.

2. Substitute sulphate of copper for iron, and the colour will be a rich brown.

3. Another blue, of quite a different tint, may be produced by letting a few drops of 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 colour.

4. Into a solution of sulphate of iron let fall a few drops of a strong infusion of galls, and the colour 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 colour, 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 colour, 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 colourless solution of corrosive sublimate (a salt of mercury) a precipitate will take place of a splendid scarlet colour, 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.[7]

Prepare separately, saturated solutions of sulphate of magnesia (Epsom salts) and carbonate of potash. On mixing them the result will be nearly solid.

[7] Saturated solutions are made by adding the salt to _boiling_ water
until it will take up no more, letting it stand till cold and then
pouring off the liquid.

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 colour.

The greater number of salts have a tendency to assume regular forms, or become _crystallised_, when passing from the fluid to the solid state; and the size and regularity of the crystals depends 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 centre 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, &c.; 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 COLOUR PRODUCED BY COLOURLESS LIQUIDS.

Make a strong infusion of the leaves of the red cabbage, which will be of a beautiful _blue_ colour; drop into it a few drops of dilute sulphuric acid, and the colour will change to a bright red; add some solution of carbonate of potash, or soda, and the red colour will gradually give way to the original blue; continue adding the alkaline solution, and the fluid will assume a bright _green_ colour. Now resume the acid, and as it is dropped in, the colour will again change from green to blue, and from blue to red. Now this simple experiment illustrates three points: first, that acids change the colour 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 colour, and become what is called a _neutral_ salt, _i. e._ a compound possessing the properties of _neither_ of its constituents.

ELECTRICITY.

No branch of science is more capable of affording amusement, combined with instruction, than electricity, and there are few sciences in which the experiments are more easily performed. We would therefore especially recommend it to our young friends.

The term electricity is derived from the Greek word _electron_, signifying amber, because electrical attraction was first discovered from its being noticed that when amber was rubbed into a certain degree of warmth, it had the power of attracting small bodies to itself.

Electricity therefore primarily treats of the phenomena and effects produced by the friction or rubbing together of certain bodies called electrics. These consist of glass, amber, resinous matters, silks, hair, wool, feathers, various vegetable substances, and atmospheric air, and the electricity so obtained is usually called Frictional Electricity, to distinguish it from that produced by chemical action, and called Voltaic Electricity.

SIMPLE MEANS OF PRODUCING ELECTRICITY.

To show the nature of electrical action, rub a piece of sealing-wax or amber upon the coat-sleeve, and it will attract light bodies, such as straws or small pieces of paper. If a clean glass tube be rubbed several times through a silken or leather cloth, and presented to any small substances, it will immediately attract and then repel them; and if a poker suspended by a dry silk string be presented to its upper end, then the lower end of the poker will exhibit the same phenomena as the tube itself, which shows that the opposite electrical condition may be induced upon other bodies by the mere neighbourhood and approach of another electrified body, and the effect so produced is called induced electricity.

When an electrified conductor is supported by non-conductors, so that the electric fluid cannot pass from the conductor to the earth, it is said to be insulated: thus the human body is a conductor of electricity--but if a person standing on a glass stool (as represented in the drawing) be charged with electricity, the electric fluid cannot pass from him to the earth, and he is said to be _insulated_; and if he be touched by another person standing on the ground, sparks will be exhibited at the point of contact, where also the person touching will feel a pricking sensation.

ATTRACTION AND REPULSION EXHIBITED.

In order to illustrate certain remarkable facts in this science of an amusing character, attention must be directed to the figure A B, which is a metal stand; C is a small piece of cork or pith, which is suspended from the hook by a dry silken thread. Having rubbed an electric, as a dry rod of glass, and presented it to C, the ball will be instantaneously attracted to the glass and will adhere to it. After they remain in contact for a few seconds, if the glass be withdrawn without being touched by the fingers, and again presented to the ball, the latter will be _repelled_ instead of attracted, as in the first instance. By being touched with the finger, the ball can be deprived of its electricity, and if after this has been done we present a piece of sealing-wax in the place of the glass formerly employed, the very same phenomena will take place. On the first application the ball will be _attracted_, and on the second _repelled_.[8]

[8] For a more complete account of this interesting science we would
refer the young reader to “The Boy’s Playbook on Science,” or, if
more advanced, to “Noad’s Manual of Electricity.”

Before the young reader can perform any very important experiments with electricity, he must become possessed of an ELECTRICAL MACHINE, which is an instrument contrived for the purpose of rubbing together the surfaces of glass and leather. They generally consist of a cylinder, or plate of glass, and a piece of silk or leather for it to rub against, covered with an amalgam, the method of preparing which we shall hereafter describe.

HOW TO MAKE AN ELECTRICAL MACHINE.

It is very easy to make a glass machine of the cylindrical form, if the maker cannot afford to buy one. First procure a common wine bottle of good dimensions, and thickish glass. Drill a hole through its bottom, with a file moistened with dilute sulphuric acid. A blacksmith, if supplied with the acid, would undertake to do this part of the work. Through this hole and the mouth pass a spindle, as represented in the cut. The end of B should be squared to fix a handle on, and the spindle should be fixed firmly in the bottle. The bottle is then to be fixed in a frame in the following manner: the end of the spindle C passes through a hole at B; and the other end at C has the handle for turning the machine.

Next make a cushion of wash-leather stuffed with wool, and fastened to the top of a frame of the following figure. This frame is to be of such a height that the cushion shall press against the sides of the bottle, and a piece of black silk is sewn on to the top of the cushion, and hangs over the bottle D. The cushion should be smeared with an amalgam, formed by melting together in the bowl of a tobacco-pipe one part of tin with two of zinc; to which, while fluid, should be added six parts of mercury. These should be stirred about till quite cold, and then reduced to a fine powder in a mortar, and mixed with a sufficient quantity of lard to form a thickish paste. When all is done, the machine is complete.

THE CONDUCTOR.

The electricity being generated by the friction produced between the rubber and the bottle from the motion imparted by the handle, it is necessary to draw it off for use. This is performed by what is called a conductor. This is made by covering a cylinder of turned wood six inches long and two and a half inches in diameter, and nicely rounded at the ends, with tinfoil, which is then mounted on a stand on a glass rod. When used, it is to be placed in the direction of the length. In it some pins are inserted, with the points outside, in a line even with, and about half an inch from, the bottle, and it should be of such a height as to come just below the silk apron. When it is wished to charge a Leyden jar, it is to be placed at the round end of the conductor. By these simple means a great variety of pleasing experiments may be performed; but to show the various phenomena connected with this interesting study, we shall now describe an electrical machine of the newest construction, and perform our experiments with it.

THE PLATE ELECTRICAL MACHINE.

Formerly the electrical machine was made in the form of a cylinder, but now it consists of a plate A, as seen in the engraving. The plate is turned by the handle F through the rubber B B, which diffuses the excitement over the glass. The points or balls at each side of the plate carry off a constant stream of positive electricity to the prime conductor C. Negative electricity is generated by insulating the conductor to which the cushion is attached, and continuing the prime conductor with the ground, so as to carry off the fluid collected from the plate.

HOW TO DRAW SPARKS FROM THE TIP OF THE NOSE.

If the person who works the machine be supported on a stool having glass legs, and connected with the conductor by means of a glass rod, the electricity will pass from the conductor to him, and as it cannot get away, owing to the glass on which he stands being a non-conductor, any person on touching him can draw the electricity from him, which will exhibit itself in small sparks as it passes to the person who touches him. If touched on the nose, sparks of fire will issue from it.

HOW TO CHARGE A LEYDEN JAR.

A most useful piece of electrical apparatus is called the Leyden jar, here represented. It is employed for the purpose of obtaining a quantity of electricity, which may be applied to any substance. It consists of a glass jar, coated both inside and without, four-fifths of the way up, with tinfoil. A knob rises through a wooden top communicating with the inside of the jar. When it is wished to charge the jar, this knob is applied to the prime conductor of the electrical machine when in action, and a quantity of electricity being given off, the jar will remain charged with it till a connexion is made, by some good conductor of electricity, between the knob and the outside tinfoil. A piece of brass chain must hang from the stem that carries the knob, and connect it with the interior of the jar.

THE ELECTRICAL BATTERY.

If several of these jars be united, a large quantity of electricity can be collected; but, in arranging them, all the interior coatings must be made to communicate by metallic rods, and a similar union must be effected among the exterior coatings. When thus arranged, the whole series may be charged as if they formed but one jar.