Nitro-Hydrochloric Acid
Symbol, NO4 + Cl.
This liquid is the Aqua-Regia of the old alchemists. It is produced by mixing Nitric and Hydrochloric Acids: the Oxygen contained in the former combines with the Hydrogen of the latter, forming water and liberating Chlorine, thus:—
NO5 + HCl = NO4 + HO + Cl.
The presence of free Chlorine confers on the mixture the power of dissolving Gold and Platinum, which neither of the two acids possesses separately. In preparing Aqua-Regia it is usual to mix one part, by measure, of Nitric Acid with four of Hydrochloric Acid, and to dilute with an equal bulk of water. The application of a gentle heat assists the solution of the metal; but if the temperature rises to the boiling point, a violent effervescence and escape of Chlorine takes place.
NITRO-SULPHURIC ACID.
For the chemistry of this acid liquid, see page 77.
OXYGEN.
Symbol, O. Atomic weight, 8.
Oxygen gas may be obtained by heating Nitrate of Potash to redness, but in this case it is contaminated with a portion of Nitrogen. The salt termed Chlorate of Potash (the composition of which is closely analogous to that of the Nitrate, Chlorine being substituted for Nitrogen) yields abundance of pure Oxygen gas on the application of heat, leaving behind Chloride of Potassium.
Chemical Properties.—Oxygen combines eagerly with many of the chemical elements, forming Oxides. This chemical affinity however is not well seen when the elementary body is exposed to the action of Oxygen in the gaseous form. It is the nascent Oxygen which acts most powerfully as an oxidizer. By nascent Oxygen is meant Oxygen on the point of separation from other elementary atoms with which it was previously associated; it may then be considered to be in the liquid form, and hence it comes more perfectly into contact with the particles of the body to be oxidized.
Illustrations of the superior chemical energy of nascent Oxygen are numerous, but none perhaps are more striking than the mild and gradual oxidizing influence exerted by atmospheric air, as compared with the violent action of Nitric Acid and bodies of that class which contain Oxygen loosely combined.
OXYMEL.
This syrup of Honey and Vinegar is prepared as follows. Take of
| Honey | 1 | pound. |
| Acid, Acetic, fortiss. (Beaufoy’s Acid) | 11 | drachms. |
| Water | 13 | drachms. |
Stand the pot containing the Honey in boiling water until a scum rises to the surface, which is to be removed two or three times. Then add the Acetic Acid and water, and skim once more if required. Allow to cool, and it will be fit for use.
POTASH.
Symbol, KO + HO. Atomic weight, 57.
Potash is obtained by separating the Carbonic Acid from Carbonate of Potash by means of Caustic Lime. Lime is a more feeble base than Potash, but the Carbonate of Lime, being insoluble in water, is at once formed on adding Milk of Lime to a solution of Carbonate of Potash (see page 314).
Properties.—Usually met with in the form of solid lumps, or in cylindrical sticks, which are formed by melting the Potash and running it into a mould. It always contains one atom of water, which cannot be driven off by the application of heat.
Potash is soluble almost to any extent in water, much heat being evolved. The solution is powerfully alkaline (p. 308), and acts rapidly upon the skin; it dissolves fatty and resinous bodies, converting them into soaps. Solution of Potash absorbs Carbonic Acid quickly from the air, and should therefore be preserved in stoppered bottles; the glass stoppers must be wiped occasionally, in order to prevent them from becoming immovably fixed by the solvent action of the Potash upon the Silica of the glass.
The Liquor Potassæ of the London Pharmacopœia has a sp. gr. of 1·063, and contains about 5 per cent, of real Potash. It is usually contaminated with Carbonate of Potash, which causes it to effervesce on the addition of acids; also, to a less extent, with Sulphate of Potash, Chloride of Potassium, Silica, etc.
POTASH, CARBONATE OF.
Symbol, KO CO2. Atomic weight, 70.
The impure Carbonate of Potash, termed Pearlash, is obtained from the ashes of wood and vegetable matter, in the same manner as Carbonate of Soda is prepared from the ashes of seaweeds. Salts of Potash and of Soda appear essential to vegetation, and are absorbed and approximated by the living tissues of the plant. They exist in the vegetable structure, combined with organic acids in the form of salts, like the Oxalate, Tartrate, etc., which, when burned are converted into Carbonates.
Properties.—The Pearlash of commerce contains large and variable quantities of Chloride of Potassium, Sulphate of Potash, etc. A purer Carbonate is sold, which is free from Sulphates, and with only a trace of Chlorides. Carbonate of Potash is a strongly alkaline salt, deliquescent, and soluble in twice its weight of cold water; insoluble in Alcohol, and employed to deprive it of water (see page 196).
PYROGALLIC ACID.
Symbol, C8H4O4 (Stenhouse). Atomic weight, 84.
The chemistry of Pyrogallic Acid has been described at page 28.
SEL D’OR. See Gold, Hyposulphite of.
SILVER.
Symbol, Ag. Atomic weight, 108.
This metal, the Luna or Diana of the alchemists, is found native in Peru and Mexico; it occurs also in the form of Sulphuret of Silver.
When pure it has a sp. gr. of 10·5, and is very malleable and ductile; melts at a bright red heat. Silver does not oxidize in the air, but when exposed to an impure atmosphere containing traces of Sulphuretted Hydrogen, it is slowly tarnished from formation of Sulphuret of Silver. It dissolves in Sulphuric Acid, but the best solvent is Nitric Acid.
The standard coin of the realm is an alloy of Silver and Copper, containing about one-eleventh of the latter metal.
To prepare pure Nitrate of Silver from it, dissolve in Nitric Acid and evaporate until crystals are obtained. Then wash the crystals with a little dilute Nitric Acid, redissolve them in water, and crystallize by evaporation a second time. Lastly, fuse the product at a moderate heat, in order to expel the last traces of Nitric and Nitrous Acids.