The Boy's Playbook of Science Part 15

Another and still more expeditious mode of preparing a little chlorine, is by placing a small beaker gla.s.s, containing half an ounce of chlorinated lime, usually termed chloride of lime or bleaching powder, carefully at the bottom of a deep and large beaker gla.s.s, and then, by means of a tube and funnel, conveying to the chloride of lime some dilute oil of vitriol, composed of half acid and half water; effervescence immediately occurs from the escape of chlorine gas, and as it is produced it falls over the sides of the small beaker gla.s.s into the large one, when it may be distinguished by its green colour. If a little gas be dipped out with a very small beaker gla.s.s arranged as a bucket, and poured into a cylindrical gla.s.s containing some dilute solution of indigo, and shaken therewith, the colour disappears almost instantaneously; and if a piece of Dutch metal is thrown into the beaker gla.s.s it will take fire if enough chlorine has been generated, or some very finely-powdered antimony will demonstrate the same result. Thus, with a few beaker gla.s.ses, some chloride of lime, sulphuric acid, a solution of indigo, and a little Dutch metal, the chief properties of chlorine may be displayed. (Fig. 132.)

[Ill.u.s.tration: Fig. 132. A A. The large beaker gla.s.s. B. The small one, containing the chloride of lime. C. The tube and funnel down which the dilute sulphuric acid is poured. D D. Sheet of paper over top of large gla.s.s, with hole in centre to admit the tube. E. The little beaker used as a bucket.]

_Fourth Experiment._

Into a little platinum spoon place a small pellet of the metal sodium, and after heating it in the flame of a spirit lamp, introduce the metal [Page 133] into a bottle of chlorine, when a most intense and brilliant combustion occurs, throwing out a vivid yellow light, and the heat is frequently so great that the bottle is cracked. After the combustion, and when the bottle is cool, it is usually lined with a white powder, which will be found to taste exactly the same as salt, and, in fact, is that substance, produced by the combination of chlorine, a virulent poison, with the metal sodium, which takes fire on contact with a small quant.i.ty of water; and hence the use of salt for the preparation of chlorine gas when it is required on the large scale.

Parts.

Common salt 4 Black oxide of manganese 1 Sulphuric acid 2 Water 2

_Fifth Experiment._

Some Dutch metal, or powdered antimony, or a bit of phosphorus, immediately takes fire when introduced into a bottle containing chlorine gas, forming a series of compounds termed chlorides, and demonstrating by the evolution of heat and light, the energetic character of chlorine, and that oxygen is not the only supporter of combustion; chlorine gas has even, in some cases, greater chemical power, because some time elapses before phosphorus will ignite in oxygen gas, whilst it takes fire directly when placed in a bottle of chlorine.

_Sixth Experiment._

The weight and bleaching power of chlorine are well shown by placing a solution of indigo in a tall cylindrical gla.s.s, leaving a s.p.a.ce at the top of about five inches in depth. By inverting a bottle of chlorine over the mouth of the cylindrical gla.s.s, it pours out like water, being about two and a half times heavier than atmospheric air, and then, after placing a ground gla.s.s plate over the top of the gla.s.s, the chlorine is recognised by its colour, whilst the bleaching power is demonstrated immediately the gas is shaken with the indigo solution.

_Seventh Experiment._

As a good contrast to the last experiment, another cylindrical jar of the same size may be provided, containing a solution of iodide of pota.s.sium with some starch, obtained by boiling a teaspoonful of arrowroot with some water; any chlorine left in the bottle (sixth experiment) may be inverted into the top of this gla.s.s and shaken, when it turns a beautiful purple blue in consequence of the liberation of iodine by the chlorine, whose greater affinity for the base produces this result. The colour is caused by the union of the iodine and the starch, which form together a beautiful purple compound, and thus the apparent anomaly of destroying and producing colour with the same agent is explained.

[Page 134]

_Eighth Experiment._

Dry chlorine does not bleach, and this fact is easily proved by taking a perfectly dry bottle, and putting into it two or three ounces of fused chloride of calcium broken in small lumps, then if a bottle full of chlorine is inverted over the one containing the chloride of calcium, taking the precaution to arrange a few folds of blotting paper with a hole in the centre on the top of the latter to catch any water that may run out of the chlorine bottle at the moment it is inverted, the gas will be dried by contact with the chloride of calcium, and if a piece of paper, with the word chlorine written on it with indigo, and previously made hot and dry, is placed in the chlorine, no change occurs, but directly the paper is removed, dipped in water, and placed in a bottle of damp chlorine, the colour immediately disappears. (Fig. 133.)

[Ill.u.s.tration: Fig. 133. A A. Dry bottle, containing chloride of calcium. B. Bottle of chlorine. The arrow indicates the gas. C C. The blotting-paper, to catch any water from the bottle, B. D. The bottle closed, and containing the paper.]

This experiment shows that chlorine is only the means to the end, and that it decomposes water, setting free oxygen, which is supposed to exert a high bleaching power in its _nascent_ state, a condition which many gases are imagined to a.s.sume just before they take the gaseous state, a sort of intermediate link between the solid or fluid and the gaseous condition of matter. The nascent state may possibly be that of ozone, to which we have already alluded as a powerful bleaching agent.

_Ninth Experiment._

A piece of paper dipped in oil of turpentine emits a dense black smoke, and frequently a flash of fire is perceptible, directly it is plunged into a bottle containing chlorine gas; here the gas combines only with the hydrogen of the turpentine, and the carbon is deposited as soot.

_Tenth Experiment._

If a lighted taper is plunged into a bottle of chlorine it continues to burn, emitting an enormous quant.i.ty of smoke, for the reason already explained, and demonstrating the perfection of the atmosphere in which [Page 135] we live and breathe, and showing that had oxygen gas possessed the same properties as chlorine, the combustion of compounds of hydrogen and carbon would have been impossible, in consequence of the enormous quant.i.ty of soot which would have been produced, so that some other element that would freely enter into combination with it must have been provided to produce both artificial light and heat. Chlorine is a gas which cannot be inhaled, and ozone presents the same features, as a mouse confined for a short time with an excess of ozone soon died; but ozone is the extraordinary condition of oxygen; the element in the ordinary state is harmless, and is the one which enters so largely into the composition of the air we breathe.

_Eleventh Experiment._

When one volume of olefiant gas (prepared by boiling one measure of alcohol and three of sulphuric acid) is mixed with two volumes of chlorine, and the two gases agitated together in a long gla.s.s vessel for a few seconds, with a gla.s.s plate over the top, which should have a welt ground perfectly flat, they unite on the application of flame, with the production of a great cloud of black smoke, arising from the deposited carbon, whilst a sort of roaring noise is heard during the time that the flame pa.s.ses from the top to the foot of the gla.s.s. (Fig. 134.)

[Ill.u.s.tration: Fig. 134. Remarkable deposition of carbon during the combustion of one volume of olefiant gas with two of chlorine.]

_Twelfth Experiment._

Formerly Bandannah handkerchiefs were in the highest estimation, and no gentleman's toilet was thought complete without one. The pattern was of the simplest kind, consisting only of white spots on a red or other coloured ground. These spots were produced in a very ingenious manner by Messrs. Monteith, of Glasgow, by pressing together many layers of silk with leaden plates perforated with holes; a solution of chlorine was then poured upon the upper plate, and pressure being applied it penetrated the whole ma.s.s in the direction of the holes, bleaching out the colour in its pa.s.sage. This important commercial result may be imitated on the small scale by placing a piece of calico dyed with Turkey red between two thick pieces of board, each of which is [Page 136] perforated with a hole two inches in diameter, and corresponding accurately when one is placed upon the other. The pieces of board may be squeezed together in any convenient way, either by weights, strong vulcanized india-rubber bands or screws, and when a strong solution of chlorine gas or of chloride of lime is poured into the hole and percolates through the cloth, the colour is removed, and the part is bleached almost instantaneously by first wetting the calico with a little weak acid, and then pouring on the solution of chloride of lime.

On removing and was.h.i.+ng the folded red calico it is found to be bleached in all the places exposed to the solution, and is now covered with white spots. (Fig. 135.)

[Ill.u.s.tration: Fig. 135. A. Circular hole in the upper piece of wood, a similar one being perforated in the lower one. B B. The strong india-rubber bands. The bleaching solution is poured into A.]

IODINE.

Iodine ([Greek: _Iodes_], violet coloured). Symbol, I; combining proportion, 127.1; specific gravity, 4.948. Specific gravity of iodine vapour, 8.716.

In the previous chapter, devoted to the element chlorine, little or nothing has been said of that inexhaustible storehouse of chlorine, iodine, and bromine--viz., the boundless ocean. Some one has remarked that, as it is possible the air may contain a little of everything capable of a.s.suming the gaseous form, so the ocean may hold in a state of solution a modic.u.m of every soluble substance, in proof of which we have lately read of some very important experiments resulting in the separation of the metal silver from sea water, not certainly in any profitable quant.i.ty, but quite enough to prove its presence in the ocean.

No elaborate research is necessary to ascertain the presence of chlorine, when it is remembered that Schafhautl has calculated, that all the oceans on the globe contain three millions fifty-one thousand three hundred and forty-two cubic geographical miles of salt, or about five times more than the ma.s.s of the Alps.

Now, salt contains about 60 per cent. of chlorine gas, and therefore the bleachers can never stand still for want of it; but iodine is not so plentiful, and was discovered by M. Courtois, of Paris, in _kelp_, a substance from which he prepared carbonate of soda, or was.h.i.+ng soda; but as this is now more cheaply prepared from common salt, the kelp is at present required only for the iodine salts it contains, as also for the chloride of pota.s.sium. Kelp is obtained by burning dried sea-weeds in a [Page 137] shallow pit; the ashes acc.u.mulate and melt together, and this fused ma.s.s broken into lumps forms kelp. The ocean bed no doubt has its fertile and barren plains and mountains, and amongst the so-called "oceanic meadows" are to be mentioned the two immense groups and bands of sea-weed called the Sarga.s.so Sea, which occupy altogether a s.p.a.ce exceeding six or seven times the area of Germany.

The iodine is contained in the largest proportion in the deep sea plants, such as the long elastic stems of the fucus palmatus, &c. The kelp is lixiviated with water, and after separating all the crystallizable salts, there remains behind a dense oily-looking fluid, called "iodine ley," to which sulphuric acid is added, and after standing a day or two the acid "ley" is placed in a large leaden retort, and heated gently with black oxide of manganese. The chlorine being produced very slowly, liberates the iodine, as already demonstrated in experiment seven, p. 133, and it is collected in gla.s.s receivers.

Iodine, when quite pure and well crystallized, has a most beautiful metallic l.u.s.tre, and presents a bluish-black colour, affording an odour which reminds one at once of the "sea smell."

_First Experiment._

A few grains of iodine placed in a flask may be sublimed at a very gentle heat, and afford a magnificent violet vapour, which can be poured out of the flask into a warm bottle. If the bottle is cold the iodine condenses in minute and brilliant crystals. (Fig. 136.)

[Ill.u.s.tration: Fig. 136. A. Flask containing iodine heated by spirit lamp. B. Cold flask above to receive the vapour. C C. Sheet of cardboard to cut off the heat from the spirit lamp.]

_Second Experiment._

Upon a thin slice of phosphorus place a few small particles of iodine; the heat produced by the combination of the two elements soon causes the phosphorus to take fire.

_Third Experiment._

Heat a brick, and then throw upon it a few grains of iodine; by holding a sheet of white paper behind, the splendid violet colour of the vapour is seen to great advantage. It was by the discovery of iodine in the ashes of sponge--which had long been used as a remedy for goitre, a remarkable glandular swelling--that this element began to be used for medical purposes, and the important salt called iodide of pota.s.sium is now used in large quant.i.ties, not only in medicine, but likewise for that most fascinating art, which has made its way steadily, and is now practised so extensively, under the name of _photography_.

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THE ART OF PHOTOGRAPHY.