flask, in which a glowing taper will inflame; this gas is oxygen. After some days the water will entirely lose its odour of chlorine, and will have acquired a sour taste, and instead of bleaching blue litmus-paper, it will redden it. Three elements only were present, the constituents of water and chlorine; thus it is obvious that the chlorine must have united with the hydrogen of the water to form hydrochloric acid, the oxygen being set free:

H2O + Cl2 = 2 HC1+0.

Bottles in which chlorine-water is kept should, therefore, be protected from the light, and this can be most conveniently done by pasting black paper round them.

The bleaching and disinfecting power of chlorine is now easily explained by its strong affinity for hydrogen. All animal and vegetable substances contain hydrogen, which is taken from them by chlorine. But if a single chemical pillar falls, the whole chemical structure tumbles with it. By the abstraction of the hydrogen, the colouring matter becomes colourless, the odorous principles scentless, the morbific matter innoxious, insoluble substances are very frequently rendered soluble, &c.

Experiment 8.-Provide two bottles of chlorine, and place in one of them some dry calcium chloride. This salt eagerly absorbs water, and will thoroughly dry any gas in contact with it. In a few hours introduce a piece of blue litmuspaper into the dry chlorine; no change in the litmus will be apparent, or, at most, it will be but slightly reddened. Perform the same operation in the other bottle, and the litmus-paper will be rapidly bleached; proving that the presence of water is necessary to enable chlorine to exert its power in this respect.

Experiment 9.-Put into chlorine water some gold-leaf; it will soon disappear, as the element chlorine combines with the element gold. The combination is called auric chloride; it is soluble in water. Chlorine has a very great tendency to combine with the metals. These combinations comport themselves as salts; they are called metallic chlorides, and most of them are soluble in water.

Experiment 10.-Pour into a vessel filled with chlorine gas a little metallic antimony, in fine powder; it will fall in a

red-hot state to the bottom, as though it were a shower of fire. The red heat is caused by the violent combination of the chlorine with the antimony. The white smoke which fills the flask is the new combination formed, viz., antimonic chloride. If a fine brass wire, on which a piece of tinsel has been fastened, be introduced into chlorine gas, both will burn with vivid combustion, and with the emission of fumes. Here combustion is another name for combination with chlorine. Brass consists of zinc and copper; accordingly, chlorides of zinc and copper are formed. Both dissolve in water, and the copper chloride imparts to the solution a green tinge.

Experiment 11.-If a piece of sodium of the size of a pea is thrown into a cup containing chlorine water, it will move rapidly round, just as in common water, with a hissing noise, and finally disappear; but if a sufficient quantity of the chlorine was present, the liquid will not afterwards give a basic reaction, as in Experiments 1 and 2, Hydrogen; neither will it have an alkaline, but a saline taste. If allowed to evaporate gradually over a warm stove, small cubic crystals remain behind, the constituents of which are chlorine and sodium. Thus, from these two elements a salt has been formed, familiarly known as common salt, NaCl.

Chlorine, like oxygen and sulphur, often unites in several proportions with a substance. Thus, there are two different chlorides of mercury.

HYDROCHLORIC ACID, HCl.

Experiment 1.-Put into a porcelain capsule a few grains of common salt, and pour a little sulphuric acid upon it; there escapes, with effervescence, a gas, which has an acid taste, fumes in the air, and reddens moistened blue test-paper; this gas is muriatic acid, or hydrochloric acid. If you pour some ammonia upon a shaving, and wave the latter to and fro over the capsule, a thick white smoke is formed; and the odour of both the hydrochloric acid, and also the pungent fumes of the ammonia, vanish. The two gases combine and form solid ammonium chloride:

Experiment 2.-Mix carefully in a flask a quarter of an ounce of water with three-quarters of an ounce of sulphuric

acid, and after the mixture has become cold, add to it half an ounce of common salt. Adapt to the neck of the flask a cork Fig. 43.

provided with a glass tube, the long limb of which passes into a phial, containing one ounce of water. If you heat the flask in a sand-bath, the hydrochloric acid escapes, but more quietly than in the former experiment, because the sulphuric acid has been somewhat diluted. The tube must only just dip into the water; for should it reach to the bottom of the phial, the whole liquid might suddenly flow back into the flask, if the heat should chance to slacken, as it might, for instance, from the flickering of the lamp by an accidental current of air. The hydrochloric acid is so eagerly absorbed by the water, that, when the evolution of the gas diminishes, a vacuum is formed in the tube and flask; the pressure of the exterior air then forces the water up into the flask (page 54). When a gaseous body condenses into a liquid, it no longer requires the latent heat by which it became gas or vapour, and therefore this heat is set free. From this it follows that the water in which the muriatic acid condenses or dissolves must soon become warm. But warm water takes up much less gas than cold; accordingly, in order to obtain a concentrated solution of hydrochloric acid gas, we must place the phial in a basin of cold water. When the liquid in the receiver has sufficiently increased, one of the blocks must be withdrawn from beneath, so as to keep the end of the tube near the surface of the liquid. The solution thus obtained has an intensely acid taste and reaction; it is called

hydrochloric acid, but is often known by the name of muriatic acid. One measure of water absorbs more than four hundred measures of hydrochloric acid gas; the strong hydrochloric acid thus obtained fumes in the air, because a part of the gas escapes. If you heat it to boiling, then half of it escapes, and an acid only half as strong remains behind; but this is always somewhat heavier than water.

The hydrochloric acid of commerce is commonly yellow, and contaminated with sulphurous acid, sulphuric acid, chlorine, iron, and arsenic. It is manufactured from common salt and sulphuric acid; but, instead of glass vessels, large iron cylinders are employed, capable of containing some hundredweights of common salt. The gas is conducted into several bottles or jars filled with water, and connected with each other. When the water in the first vessel becomes saturated with the hydrochloric acid gas, the gas passes over into the second, then into the third vessel, and so on, saturating each successively. This is a Fig. 44.

very convenient method of
conducting gases through
liquids. Such vessels, which
are commonly provided with
two or three necks, are called
Woulfe's bottles.
The up-
right tube in the middle
neck serves as a safety tube,
that is, it prevents the liquid

from being forced back; if a vacuum is formed in one of the bottles, the air enters through this tube.

Experiment 3.-If instead of dipping into water, the delivery-tube is passed to the bottom of a dry bottle, the heavy gas will displace the air, and fill the bottle. Its solubility may then be shown by inverting the bottle quickly in water. The water will rush up and fill the bottle.

Common salt consists of chlorine and sodium. With sulphuric acid the following change takes place :

The constituents of hydrochloric acid gas are equal atoms of chlorine and hydrogen, and it is represented by the formula HCl.

If you fill a glass vessel half with chlorine and half with hydrogen, and put it in a dark place, no union ensues; but it takes place instantaneously when a light is applied or when the vessel is exposed to the direct rays of the sun. The union is accompanied by a violent detonation, which often breaks the vessel, so that it is not advisable to perform this experiment except on a very small scale. In the dif

fused light of day the combination takes place slowly.

Experiment 4.-Put some iron nails into a phial, and pour upon them some hydrochloric acid; brisk effervescence will ensue. When this has continued some minutes, hold a burning taper over the mouth of the phial; the gas which escapes takes fire; it is hydrogen. The acid is decomposed, and its second constituent, chlorine, combines with the iron. The iron disappears, and is dissolved; that is, it combines with the chlorine, forming a soluble compound. When the effervescence has ceased, heat the phial by placing it in hot water, and afterwards pour its contents upon a filter of white blotting-paper. Put the liquid which passes through (the filtrate) in a cool place; a salt is deposited from it in greenish crystals, called ferrous chloride, FeCl2.

Many other metals are also dissolved, like iron, by muriatic acid, and converted into chlorides.

Experiment 5.-Pour some muriatic acid upon iron-rust that has been put into a test-tube; it dissolves, but without evolution of gas. In this case, the hydrogen of the hydrochloric acid meets with a body with which it can combine, namely, the oxygen of the oxide or rust of iron; and it does combine with it, forming water. The yellowish-brown solution, which it is difficult to crystallise, yields, upon evaporation, a brown mass called ferric chloride, Fe,Cl. This salt contains one half more chlorine than the former. Hydrochloric acid is very often used for dissolving metallic oxides.

Experiment 6.-Dissolve some crystals of the protochloride of iron, obtained according to Experiment 3, in a little water, and then add some chlorine water; the greenish colour is converted into a yellow colour, and the solution yields, on evaporation, brown ferric chloride. The chlorine converts the ferrous chloride into ferric chloride.

Experiment 7.--Dissolve some carbonate of soda (sodium carbonate) in water; the solution turns red test-paper blue;