sition of metals consisting chiefly of copper, which burns readily; and I use a thin metallic leaf in preference to a lump of metal, because it offers to the action of the gas but a small quantity of matter under a large surface.-Filings, or shavings, would answer the purpose nearly as well; but a lump of metal, though the surface would oxydate with great rapidity, would not take fire. Pure gold is not inflamed by oxy-muriatic acid gas, but it is rapidly oxydated, and dissolved by it; indeed, this acid is the only one that will dissolve gold.

Emily. This, I suppose, is what is commonly called aqua regia, which you know, is the only thing that will act upon gold.

Mrs. B. That is not exactly the case either; for aqua regia is composed of a mixture of muriatic and nitric acid. But, in fact, the result of this mixture is nothing more than oxy-muriatic acid, as the muriatic acid oxygenates itself at the expense of the nitric; this mixture, therefore, though it bears the name of nitro muriatic acid, acts on gold merely in virtue of the oxymuriatic acid which it contains.

Sulphur, volatile oils, and many other substances, will burn in the same manner in oxy-muriatic acid gas; but I have not prepared a sufficient quantity of it, to shew you the combustion of all these bodies.

Caroline. Yet there are several jars of the gas remaining.

Mrs. B. We must reserve these for other experiments. The oxy-muriatic acid does not, like other acids, redden the blue vegetable colours; but it totally destroys any colour, and turns all vegetables perfectly white. Let us collect some vegetable substances to put into this glass which is full of gas.

Emily. Here is a sprig of myrtle

Caroline. And here some coloured paper

Mrs. B. We shall also put in this piece of coquelicot ribbon, and a rose→

Emily. Their colours begin to fade immediately! But how does the gas produce this effect?

Mrs. B. The oxygen combines with the colouring

matter of these substances, and destroys it; that is to say, destroys the property which these colours had of reflecting only one kind of rays, and renders them capable of reflecting them all, which, you know, will make them appear white. Old prints may be cleaned by this acid, for the paper will be whitened without injuring the impression, as printer's ink is made of materials (oil and lamp black) which are not acted upon by acids.

This property of the oxy-muriatic acid has lately been employed in manufactories in a variety of bleaching processes; but for these purposes the gas must be dissolved in water, as the acid is thus rendered much milder and less powerful in its effects; for, in a gase ous state, it would destroy the texture, as well as the colour, of the substance submitted to its action.

Caroline. Look at the things which we put into the gas; they have now entirely lost their colour!

Mrs. B. The effect of the acid is almost completed -and, and if we were to examine the quantity that remains, we should find it consist chiefly of muriatic acid.

The oxy-muriatic acid has been used to purify the air in fever hospitals and prisons, as it burns and destroys putrid effluvia of every kind. The infection of the small pox is likewise destroyed by this gas, and matterthat has been submitted to its influence will no longer generate that disorder.

Caroline. Indeed, I think the remedy must be neare ly as bad as the disease; the oxy-muriatic acid has such a dreadful suffocating smell.

Mrs. B. It is certainly extremely offensive; but, by keeping the mouth shut, and wetting the nostrils with liquid ammonia, in order to neutralize the vapour as it reaches the nose, its prejudicial effects may be in some degree prevented. At any rate, however, this mode of disinfection can hardly be used in places that are inhabited. And as the vapour of nitric acid, which is scarcely less efficacious for this purpose, is not at all prejudicial, it is usually preferred on such occasions.

Amongst the compound salts formed by muriatic acid, the muriat of soda, or common salt, is the most

interesting. The uses and properties of this salt are too well known to require much comment. Besides the pleasant flavour it imparts to the food, it is very wholesome, when not used to excess, as it greatly assists the process of digestion.

Sea-water is the great source from which the muriat of soda is extracted by evaporation. But it is found also in large solid masses in the bowels of the earth, in England, and in many other parts of the world.

Emily. I thought that salts, when solid, were al

ways in a state of crystals; but the common table salt is in the form of a coarse white powder.

Mrs. B. Crystallization depends, as you may recollect, on the slow and regular reunion of particles dissolved in a fluid; common sea salt is only in a state of imperfect crystallization, because the process by which it is prepared is not favorable to the formation of regular crystals. But, if you melt it, and afterwards evaporate the water slowly, you will obtain a regular crystallization.

Muriat of ammonia is another combination of this acid, which we have already mentioned as the principal source from which ammonia is derived.

I can at once shew you the formation of this salt by the immediate combination of muriatic acid with ammonia. These two glass jars contain, the one muriatic acid gas, the other ammoniacal both of which are gas, perfectly invisible-now, if I mix them together, you see they immediately form an opaque white cloud like smoke. If a thermometer were placed in the jar in which these gasses are mixed, you would perceive that some heat is at the same time produced.

Emily. The effects of chemical combinations are, indeed, wonderful-how extraordinary it is that two invisible bodies should become visible by their union.

Mrs. B. This strikes you with wonder because it is a phenomenon which nature seldom exhibits to our view; but the most common of her operations are as wonderful, and it is their frequency only that prevents our regarding them with equal admiration. What

would be more surprising for instance, than combustion, were it not rendered so familiar by custom ?

Emily. That is true.-But pray, Mrs. B. is this white cloud the salt that produces ammonia? How different it is from the solid muriat of ammonia which you once shewed us !

Mrs. B. It is the same substance which first appears in the state of vapour, but will soon be condensed, by cooling against the sides of the jar, in the form of very minute crystals.

We may now proceed to the oxy-muriats. In this class of salts the oxy-muriat of potash is the most worthy of our attention, for its striking properties. The acid, in this state of combination, contains a still greater proportion of oxygen than when alone.

Caroline. But how can the oxy-muriatic acid acquire an increase of oxygen by combining with potash?

Mrs. B. It does not really acquire an additional quantity of oxygen, but it loses some of the muriatic acid, which produces the same effect, as the acid that remains is proportionably super-oxygenated.

If this salt be mixed, and merely rubbed together with sulphur, phosphorus, charcoal, or indeed any other combustible, it explodes strongly.

Caroline. Like gunpowder, I suppose, it is suddenly converted into elastic fluids ?

Mrs. B. Yes; but with this remarkable difference, that no increase of temperature, any further than is produced by the gentle friction, is required in this instance. Can you tell me what gasses are generated by the detonation of this salt with charcoal?

Emily. Let me consider...... The oxy muriatic acid parts with its excess of oxygen to the charcoal, by which means it is converted into muriatic acid gas; whilst the charcoal, being burnt by the oxygen, is changed to carbonic acid gas-What becomes of the potash I cannot tell.

Mrs. B. the vessel.

That is a fixed product which remains in

Caroline. But since the potash does not enter into the new combinations, I do not understand of what use

it is in this operation. Would not the oxy-muriatic acid and the charcoal produce the same effect without it?

Mrs. B. No; because there would not be that very great concentration of oxygen which the combination with the potash produces, as I have just explained.

I mean to shew you this experiment, but I would advise you not to repeat it alone; for if care be not taken to mix only very small quantities at a time, the detonation will be extremely violent, and may be attended with dangerous effects. You see I mix an exceedingly small quantity of the salt with a little powdered charcoal, in this Wedgwood mortar, and rub them together with the pestle

Caroline. Heavens! How can such a loud explosion be produced by so small a quantity of matter?

Mrs. B. You must consider that an extremely small quantity of solid substance may produce a very great volume of gasses; and it is the sudden evolution of these which occasions the sound.

Emily. Would not oxy-muriat of potash make stronger gunpowder than nitrat of potash ?

Mrs. B. Yes; but the preparation as well as the use of this salt, is attended with so much danger, that it is never employed for that purpose.

Caroline. There is no cause to regret it, I think; for the common gunpowder is quite sufficiently destructive.

Mrs. B. I can shew you a very curious experiment with this salt; but it must again be on condition that you will never attempt to repeat it by yourselves. I throw a small piece of phosphorus into this glass of water; then a little oxy-muriat of potash; and, lastly, I pour in, by means of this funnel, so as to bring it in contact with the two other ingredients in the bottom of the glass, a small quantity of sulphuric acid

Caroline. This is indeed, a beautiful experiment ! the phosphorus takes fire and burns from the bottom of the water.

Emily. How wonderful it is to. see flame bursting