Every Boy's Book: A Complete Encyclopaedia of Sports and Amusements Part 59

_Cla.s.s 6._ Tin cla.s.s: niobium, tantalum, tin, t.i.tanium.

_Cla.s.s 7._ Tungsten cla.s.s: molybdenum, tungsten, vanadium.

_Cla.s.s 8._ a.r.s.enic cla.s.s: antimony, a.r.s.enic, bis.m.u.th.

_Cla.s.s 9._ Lead cla.s.s: lead, thallium.

_Cla.s.s 10._ Silver cla.s.s: copper, mercury, silver.

_Cla.s.s 11._ Gold cla.s.s: gold, iridium, osmium, palladium, platinum, rhodium, ruthenium.

POTa.s.sIUM.

Pota.s.sium 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 Inst.i.tution, 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 pota.s.sium 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 pota.s.sium will be marked with a deep brown colour.--_Corollary._ Hence, if you touch pota.s.sium 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, pota.s.sium must be kept in some fluid dest.i.tute of that element, such as naphtha.

_Caution!_--As the globules of pota.s.sium 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 s.p.a.ce 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 a.s.sume 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 gla.s.s 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 quant.i.ty of _iron_, so that nitrate of _iron_ is found in the liquid. The oxygen and nitric acid remain unaltered in quant.i.ty 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 quant.i.ty 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. Subst.i.tute 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 quant.i.ty 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 a.s.sume certain definite forms in returning from the fluid to the solid state. Bis.m.u.th shows this property more readily than most others.

EXPERIMENT.

Melt a pound or two of bis.m.u.th 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 circ.u.mstance, 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 s.p.a.ce (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 quant.i.ty 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 a.s.sume regular forms, or become _crystallised_, when pa.s.sing 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.