Elements of Chemistry Part 15

Barytes Nitrat of barytes Nitre, with a base of heavy earth.

Potash potash Nitre, saltpetre. Nitre with base of potash.

Soda soda { Quadrangular nitre. Nitre with base of { mineral alkali.

{ Calcareous nitre. Nitre with Lime lime { calcareous base. Mother water { of nitre, or saltpetre.

Magnesia magnesia Magnesian nitre. Nitre with base of magnesia.

Ammoniac ammoniac Ammoniacal nitre.

{ Nitrous alum. Argillaceous nitre. Nitre Argill argill { with base of earth of alum.

Oxyd of zinc zinc Nitre of zinc.

iron iron Nitre of iron. Martial nitre. Nitrated iron.

manganese manganese Nitre of manganese.

cobalt cobalt Nitre of cobalt.

nickel nickel Nitre of nickel.

lead lead Saturnine nitre. Nitre of lead.

tin tin Nitre of tin.

copper copper Nitre of copper or of Venus.

bis.m.u.th bis.m.u.th Nitre of bis.m.u.th.

antimony antimony Nitre of antimony.

a.r.s.enic a.r.s.enic a.r.s.enical nitre.

mercury mercury Mercurial nitre.

silver silver Nitre of silver or luna. Lunar caustic.

gold gold Nitre of gold.

platina platina Nitre of platina.

SECT. XIII.--_Observations upon the Nitrous and Nitric Acids, and their Combinations._

The nitrous and nitric acids are procured from a neutral salt long known in the arts under the name of _saltpetre_. This salt is extracted by lixiviation from the rubbish of old buildings, from the earth of cellars, stables, or barns, and in general of all inhabited places. In these earths the nitric acid is usually combined with lime and magnesia, sometimes with potash, and rarely with argill. As all these salts, excepting the nitrat of potash, attract the moisture of the air, and consequently would be difficultly preserved, advantage is taken, in the manufactures of saltpetre and the royal refining house, of the greater affinity of the nitric acid to potash than these other bases, by which means the lime, magnesia, and argill, are precipitated, and all these nitrats are reduced to the nitrat of potash or saltpetre[41].

The nitric acid is procured from this salt by distillation, from three parts of pure saltpetre decomposed by one part of concentrated sulphuric acid, in a retort with Woulfe's apparatus, (Pl. IV. fig. 1.) having its bottles half filled with water, and all its joints carefully luted. The nitrous acid pa.s.ses over in form of red vapours surcharged with nitrous gas, or, in other words, not saturated with oxygen. Part of the acid condenses in the recipient in form of a dark orange red liquid, while the rest combines with the water in the bottles. During the distillation, a large quant.i.ty of oxygen gas escapes, owing to the greater affinity of oxygen to caloric, in a high temperature, than to nitrous acid, though in the usual temperature of the atmosphere this affinity is reversed. It is from the disengagement of oxygen that the nitric acid of the neutral salt is in this operation converted into nitrous acid. It is brought back to the state of nitric acid by heating over a gentle fire, which drives off the superabundant nitrous gas, and leaves the nitric acid much diluted with water.

Nitric acid is procurable in a more concentrated state, and with much less loss, by mixing very dry clay with saltpetre. This mixture is put into an earthern retort, and distilled with a strong fire. The clay combines with the potash, for which it has great affinity, and the nitric acid pa.s.ses over, slightly impregnated with nitrous gas. This is easily disengaged by heating the acid gently in a retort, a small quant.i.ty of nitrous gas pa.s.ses over into the recipient, and very pure concentrated nitric acid remains in the retort.

We have already seen that azote is the nitric radical. If to 20-1/2 parts, by weight, of azote 43-1/2 parts of oxygen be added, 64 parts of nitrous gas are formed; and, if to this we join 36 additional parts of oxygen, 100 parts of nitric acid result from the combination.

Intermediate quant.i.ties of oxygen between these two extremes of oxygenation produce different species of nitrous acid, or, in other words, nitric acid less or more impregnated with nitrous gas. I ascertained the above proportions by means of decomposition; and, though I cannot answer for their absolute accuracy, they cannot be far removed from truth. Mr Cavendish, who first showed by synthetic experiments that azote is the base of nitric acid, gives the proportions of azote a little larger than I have done; but, as it is not improbable that he produced the nitrous acid and not the nitric, that circ.u.mstance explains in some degree the difference in the results of our experiments.

As, in all experiments of a philosophical nature, the utmost possible degree of accuracy is required, we must procure the nitric acid for experimental purposes, from nitre which has been previously purified from all foreign matter. If, after distillation, any sulphuric acid is suspected in the nitric acid, it is easily separated by dropping in a little nitrat of barytes, so long as any precipitation takes place; the sulphuric acid, from its greater affinity, attracts the barytes, and forms with it an insoluble neutral salt, which falls to the bottom. It may be purified in the same manner from muriatic acid, by dropping in a little nitrat of silver so long as any precipitation of muriat of silver is produced. When these two precipitations are finished, distill off about seven-eighths of the acid by a gentle heat, and what comes over is in the most perfect degree of purity.

The nitric acid is one of the most p.r.o.ne to combination, and is at the same time very easily decomposed. Almost all the simple substances, with the exception of gold, silver, and platina, rob it less or more of its oxygen; some of them even decompose it altogether. It was very anciently known, and its combinations have been more studied by chemists than those of any other acid. These combinations were named _nitres_ by Messrs Macquer and Beaume; but we have changed their names to nitrats and nitrites, according as they are formed by nitric or by nitrous acid, and have added the specific name of each particular base, to distinguish the several combinations from each other.

TABLE _of the Combinations of Sulphuric Acid with the Salifiable Bases, in the order of affinity._

_Names of the bases._ _Resulting compounds._ _New nomenclature._ _Old nomenclature._

Barytes Sulphat of barytes Heavy spar. Vitriol of heavy earth.

Potash potash {Vitriolated tartar. Sal { de duobus. Arcanum { duplicatam.

Soda soda Glauber's salt.

Lime lime Selenite, gypsum, calcareous vitriol.

Magnesia magnesia Epsom salt, sedlitz salt, magnesian vitriol.

Ammoniac ammoniac Glauber's secret sal ammoniac.

Argill argill Alum.

Oxyd of zinc zinc {White vitriol, goslar { vitriol, white coperas, { vitriol of zinc.

iron iron {Green coperas, green { vitriol, martial vitriol, { vitriol of iron.

manganese manganese Vitriol of manganese.

cobalt cobalt Vitriol of cobalt.

nickel nickel Vitriol of nickel.

lead lead Vitriol of lead.

tin tin Vitriol of tin.

copper copper {Blue coperas, blue vitriol, { Roman vitriol, { vitriol of copper.

bis.m.u.th bis.m.u.th Vitriol of bis.m.u.th.

antimony antimony Vitriol of antimony.

a.r.s.enic a.r.s.enic Vitriol of a.r.s.enic.

mercury mercury Vitriol of mercury.

silver silver Vitriol of silver.

gold gold Vitriol of gold.

platina platina Vitriol of platina.

SECT. XIV.--_Observations upon Sulphuric Acid and its Combinations._

For a long time this acid was procured by distillation from sulphat of iron, in which sulphuric acid and oxyd of iron are combined, according to the process described by Basil Valentine in the fifteenth century; but, in modern times, it is procured more oeconomically by the combustion of sulphur in proper vessels. Both to facilitate the combustion, and to a.s.sist the oxygenation of the sulphur, a little powdered saltpetre, nitrat of potash, is mixed with it; the nitre is decomposed, and gives out its oxygen to the sulphur, which contributes to its conversion into acid. Notwithstanding this addition, the sulphur will only continue to burn in close vessels for a limited time; the combination ceases, because the oxygen is exhausted, and the air of the vessels reduced almost to pure azotic gas, and because the acid itself remains long in the state of vapour, and hinders the progress of combustion.

In the manufactories for making sulphuric acid in the large way, the mixture of nitre and sulphur is burnt in large close built chambers lined with lead, having a little water at the bottom for facilitating the condensation of the vapours. Afterwards, by distillation in large retorts with a gentle heat, the water pa.s.ses over, slightly impregnated with acid, and the sulphuric acid remains behind in a concentrated state. It is then pellucid, without any flavour, and nearly double the weight of an equal bulk of water. This process would be greatly facilitated, and the combustion much prolonged, by introducing fresh air into the chambers, by means of several pairs of bellows directed towards the flame of the sulphur, and by allowing the nitrous gas to escape through long serpentine ca.n.a.ls, in contact with water, to absorb any sulphuric or sulphurous acid gas it might contain.

By one experiment, Mr Berthollet found that 69 parts of sulphur in combustion, united with 31 parts of oxygen, to form 100 parts of sulphuric acid; and, by another experiment, made in a different manner, he calculates that 100 parts of sulphuric acid consists of 72 parts sulphur, combined with 28 parts of oxygen, all by weight.

This acid, in common with every other, can only dissolve metals when they have been previously oxydated; but most of the metals are capable of decomposing a part of the acid, so as to carry off a sufficient quant.i.ty of oxygen, to render themselves soluble in the part of the acid which remains undecomposed. This happens with silver, mercury, iron, and zinc, in boiling concentrated sulphuric acid; they become first oxydated by decomposing part of the acid, and then dissolve in the other part; but they do not sufficiently disoxygenate the decomposed part of the acid to reconvert it into sulphur; it is only reduced to the state of sulphurous acid, which, being volatilised by the heat, flies off in form of sulphurous acid gas.

Silver, mercury, and all the other metals except iron and zinc, are insoluble in diluted sulphuric acid, because they have not sufficient affinity with oxygen to draw it off from its combination either with the sulphur, the sulphurous acid, or the hydrogen; but iron and zinc, being a.s.sisted by the action of the acid, decompose the water, and become oxydated at its expence, without the help of heat.

TABLE _of the Combinations of the Sulphurous Acid with the Salifiable Bases, in the order of affinity._

_Names of the Bases._ _Names of the Neutral Salts._

Barytes Sulphite of barytes.

Potash potash.

Soda soda.