Experiment 4. If a paper be dipped in alcohol and then sprinkled with this acid, they will burn with a green flame.

The composition of this acid is unknown, if we except however the opinion of Mr. Davy, that it contains Oxygen.

SECTION VIII.

OF NITRIC ACID.

Experiment 1. If electric explosions be passed through a mixture of three measures of oxygen gas and one measure and a quarter of azotic gas, a union will take place, and nitric acid be formed. Or,

Experiment 2. If equal parts of nitrate of potash and sulphate of iron be mixed, and introduced into a retort, to which two bottles, according to the plan of Woulf's apparatus, is afterwards affixed, and the heat of a lamp applied, nitric acid with nitrous gas will be obtained. Or,

Experiment 3. If two ounces of nitrate of potash be introduced into a retort, and one ounce of sulphuric acid added, and the whole exposed to heat, the same product will come over.

Remark. The following is a more particular account of the method of obtaining nitric acid by chemists:

Take two parts of dry nitrate of potash in coarse powder, put it into a tubulated glass retort, of which it occupies no more than one third, or one-fourth, and to which a large receiver has been luted containing a little water; then pour on it, in small quantities at a time, one part of concentrated sulphuric acid. As soon as the last quantity of the acid is introduced into the retort apply a very gentle heat, and distil slowly_till no more drops issue from the neck of the retort. The acid collected in the receiver is fuming, and of a red

1

dish or yellow colour: on being brought into contact with atmospheric air, it sends forth reddish yellow fumes, which likewise always fill the empty space of the receiver or bottle. In order to deprive it of these fumes, the acid must be re-distilled, or at least heated for some time in a glass retort, with a very gentle heat; the fuming part will rise first, and the remainder will be deprived of all its colour and fuming property.

Rationale. Nitric acid, being a compound of 29.77 azote, and 70.23 oxygen, is formed in every case in which these elements unite in proper proportions. In the first experiment, a direct combination takes place. In the second and third, it is merely the disengagement of the acid from the base, with which it was previously united. When sulphate of iron is used, the heat disengages the greater part of the acid from that salt, which then decomposes the nitrate of potash, forming sulphate of potash, which remains behind, and disengages the nitric acid. When sulphuric acid itself is used, the application of heat causes it to act directly on the nitrate, by which the nitric acid is evolved.

Remark. Nitric acid appears to have been known in the time of Raymond Lully. Basil Valentine describes the process, and calls the product water of nitre. It has since been called spirit of nitre, and nitric acid. In large manufactories, it is generally obtained by distilling a mixture of nitre and clay.

Nitric acid is liquid, colourless, and transparent, possessing in a very eminent degree all the properties of acids. Its specific gravity varies; the strongest kind is about 1.5. It tinges the skin yellow, which does not disappear till the epidermis wears off. It has a strong affinity for water, and has never yet been found in nature except in combination. It produces heat when added to water. When concentrated, exhales white acrid fumes on being exposed to the air, which are nitric acid in a gazeous state. When poured on oils, charcoal, &c. it sets them on fire. See Caloric. It causes the sulphurous and phosphorous acids to pass to the state of sulphuric and phosphoric acids, by yielding to them part of its oxygen. It is capable of

oxydating all the metals except gold, platinum, titanium, and tantalium.

The changes which take place on the addition of water to strong nitrous acid exhibit very curious phenomena. Different portions change its colour to a blue, a green, a yellow, &c. while the vapours which rise from it preserve their original flame-coloured red.

Experiment 4. If 4 parts of water, by measure, be added to 12 parts of strong fuming nitrous acid, the colour will be changed from a deep orange to a green.

Experiment 5. Mix 4 measures more of water with the diluted acid produced in the last experiment, and the colour will thereby be changed to a paler green, mixed with yellow.

Experiment 6. Add 4 measures more of water to the above, and the green will disappear and a pale yellow acid will be produced.

Experiment 7. If 40 measures of water be now added to the yellow acid produced in the last experiment, you will have an acid as colourless as pure water.

SECTION IX.

OF NITROUS ACID.

Experiment 1. If colourless nitric acid be exposed to the rays of the sun, it will acquire a smoking appearance, and a yellow or brown colour, forming the nitrous acid. Or,

Experiment 2. If nitric acid be exposed to nitrous gas, the latter will be absorbed. Or,

Experiment 3. If nitre be subjected to a strong heat in an iron mattrass, in order to obtain oxygen gas, after this has passed off for some time, the residue is a salt composed of nitrous acid and potash. Consequently nitrous acid is formed.

Remark. As it is now generally admitted that nitrous acid is nitric holding nitrous gas in solution, and that the proportion of oxygen is probably less in the nitrous, we can readily account for the changes which take place when nitric acid is exposed to the sun's rays, or when nitric acid is saturated with nitrous gas; the former showing that light separates a portion of oxygen, and the latter, that nitrous gas by combining with the nitric acid, changes its colour and some of its properties. In the same manner also, the action of heat robs the nitrate of a part of its oxygen, and converts it into nitrite of potash. See Nitric Oxyd Gas.

Nitrous acid exists in the state of gas, in the form of a red vapour, slightly coercible. When combined with water it is of a yellow or orange colour. It emits copious orange-coloured or red fumes.

SECTION X.

OF OXYMURIATIC ACID.

Experiment 1. Put into a tubulated retort, support-ed over a lamp, one part of black oxyd of manganese reduced to a gross powder, and pour over it three parts of concentrated muriatic acid; recline the retort in such a manner that the fluid which rises up into its neck may easily run back again into the body, and apply a receiver with a little distilled water in it; the receiver must be luted to the retort by a fillet of paper. When the effervescence, which instantly takes place on the affusion of the acid, ceases, apply a gentle heat. Oxygenized muriatic acid gas will be evolved, and the receiver become filled with yellow vapours, which are absorbed by the water. When the water has acquired a yellowish green colour, the receiver may be removed, and another one applied till no more gas is extricated. Remark. The process may be more elegantly conducted by employing the distillatory apparatus of Mr. Hem

Experiment 2. If the same quantity of salt and acid be introduced into a retort, with 5 or 6 parts of water, and distilled, liquid muriatic acid will pass over.

Or,

Experiment 3. Put into a tubulated retort, lodged in a sand-heat, or supported over a lamp, and connected with Pepys's distillatory vessel, or Woulf's bottles, every one containing a small quantity of distilled water, three parts of muriate of soda, and pour on it one of sulphuric acid very gradually, or rather let it be suffered to drop into the retort, by means of a hydrostatic funnel fastened into its tubulure. Muriatic acid gas will be plentifully disengaged, which passes through the neck of the retort, and becomes absorbed by the water. When the water in the first bottle is fully saturated it absorbs no more, and becomes cold, being considerably heated by the absorption of the gas; but the gas continues to pass into the next bottles, and heats the water they contain. The water thus impregnated with muriatic acid gas is called muriatic acid.

Remark. If sulphuric acid diluted with an equal quantity, by weight, of water, be made use of in this process, the apparatus of Pepys or Woulf may be dispensed with, and a common receiver may be used with safety.

In all these experiments the muriatic acid is disengaged from the muriate of soda, by the sulphuric acid. The acid is nothing more than water saturated with the gas.

Liquid muriatic acid, or water saturated with this gas is about 1.196 specific gravity. The muriatic acid, or spirit of salt of commerce varies from about 1.120 to about 1.164.

Sulphuric, phosphoric, nitric, and other acids may be decomposed by charcoal; but muriatic acid is unalterable by any of the combustibles with which we are acquainted.

With various bases it forms the salts called muriates.