Elements of Chemistry Part 20

antimony antimony.

a.r.s.enic a.r.s.enic.

silver silver.

mercury mercury.

gold gold.

platina platina.

SECT. XXVI.--_Observations upon Tartarous Acid, and its Combinations._

Tartar, or the concretion which fixes to the inside of vessels in which the fermentation of wine is completed, is a well known salt, composed of a peculiar acid, united in considerable excess to potash. Mr Scheele first pointed out the method of obtaining this acid pure. Having observed that it has a greater affinity to lime than to potash, he directs us to proceed in the following manner. Dissolve purified tartar in boiling water, and add a sufficient quant.i.ty of lime till the acid be completely saturated. The tartarite of lime which is formed, being almost insoluble in cold water, falls to the bottom, and is separated from the solution of potash by decantation; it is afterwards washed in cold water, and dried; then pour on some sulphuric acid, diluted with eight or nine parts of water, digest for twelve hours in a gentle heat, frequently stirring the mixture; the sulphuric acid combines with the lime, and the tartarous acid is left free. A small quant.i.ty of gas, not hitherto examined, is disengaged during this process. At the end of twelve hours, having decanted off the clear liquor, wash the sulphat of lime in cold water, which add to the decanted liquor, then evaporate the whole, and the tartarous acid is obtained in a concrete form. Two pounds of purified tartar, by means of from eight to ten ounces of sulphuric acid, yield about eleven ounces of tartarous acid.

As the combustible radical exists in excess, or as the acid from tartar is not fully saturated with oxygen, we call it _tartarous acid_, and the neutral salts formed by its combinations with salifiable bases _tartarites_. The base of the tartarous acid is a carbono-hydrous or hydro-carbonous radical, less oxygenated than in the oxalic acid; and it would appear, from the experiments of Mr Ha.s.senfratz, that azote enters into the composition of the tartarous radical, even in considerable quant.i.ty. By oxygenating the tartarous acid, it is convertible into oxalic, malic, and acetous acids; but it is probable the proportions of hydrogen and charcoal in the radical are changed during these conversions, and that the difference between these acids does not alone consist in the different degrees of oxygenation.

The tartarous acid is susceptible of two degrees of saturation in its combinations with the fixed alkalies; by one of these a salt is formed with excess of acid, improperly called _cream of tartar_, which in our new nomenclature is named _acidulous tartarite of potash_; by a second or equal degree of saturation a perfectly neutral salt is formed, formerly called _vegetable salt_, which we name _tartarite of potash_.

With soda this acid forms tartarite of soda, formerly called _sal de Seignette_, or _sal polychrest of Roch.e.l.l_.

SECT. XXVII.--_Observations upon Malic Acid, and its Combinations with the Salifiable Bases[45]._

The malic acid exists ready formed in the sour juice of ripe and unripe apples, and many other fruits, and is obtained as follows: Saturate the juice of apples with potash or soda, and add a proper proportion of acet.i.te of lead dissolved in water; a double decomposition takes place, the malic acid combines with the oxyd of lead and precipitates, being almost insoluble, and the acet.i.te of potash or soda remains in the liquor. The malat of lead being separated by decantation, is washed with cold water, and some dilute sulphuric acid is added; this unites with the lead into an insoluble sulphat, and the malic acid remains free in the liquor.

This acid, which is found mixed with citric and tartarous acid in a great number of fruits, is a kind of medium between oxalic and acetous acids being more oxygenated than the former, and less so than the latter. From this circ.u.mstance, Mr Hermbstadt calls it _imperfect vinegar_; but it differs likewise from acetous acid, by having rather more charcoal, and less hydrogen, in the composition of its radical.

When an acid much diluted has been used in the foregoing process, the liquor contains oxalic as well as malic acid, and probably a little tartarous, these are separated by mixing lime-water with the acids, oxalat, tartarite, and malat of lime are produced; the two former, being insoluble, are precipitated, and the malat of lime remains dissolved; from this the pure malic acid is separated by the acet.i.te of lead, and afterwards by sulphuric acid, as directed above.

TABLE _of the Combinations of Citric Acid, with the Salifiable Bases, in the Order of Affinity(A)._

_Bases._ _Neutral Salts._

Barytes Citrat of barytes.

Lime lime.

Magnesia magnesia.

Potash potash.

Soda soda.

Ammoniac ammoniac.

Oxyd of zinc zinc.

manganese manganese.

iron iron.

lead lead.

cobalt cobalt.

copper copper.

a.r.s.enic a.r.s.enic.

mercury mercury.

antimony antimony.

silver silver.

gold gold.

platina platina.

Argill argill.

[Note A: These combinations were unknown to the ancient chemists. The order of affinity of the salifiable bases with this acid was determined by Mr Bergman and by Mr de Breney of the Dijon Academy.--A.]

SECT. XXVIII.--_Observations upon Citric Acid, and its Combinations._

The citric acid is procured by expression from lemons, and is found in the juices of many other fruits mixed with malic acid. To obtain it pure and concentrated, it is first allowed to depurate from the mucous part of the fruit by long rest in a cool cellar, and is afterwards concentrated by exposing it to the temperature of 4 or 5 degrees below Zero, from 21 to 23 of Fahrenheit, the water is frozen, and the acid remains liquid, reduced to about an eighth part of its original bulk. A lower degree of cold would occasion the acid to be engaged amongst the ice, and render it difficultly separable. This process was pointed out by Mr Georgius.

It is more easily obtained by saturating the lemon-juice with lime, so as to form a citrat of lime, which is insoluble in water; wash this salt, and pour on a proper quant.i.ty of sulphuric acid; this forms a sulphat of lime, which precipitates and leaves the citric acid free in the liquor.

TABLE _of the Combinations of Pyro-lignous Acid with the Salifiable Bases, in the Order of Affinity(A)._

_Bases._ _Neutral Salts._

Lime Pyro-mucite of lime.

Barytes barytes.

Potash potash.

Soda soda.

Magnesia magnesia.

Ammoniac ammoniac.

Oxyd of zinc zinc.

manganese manganese.

iron iron.

lead lead.

tin tin.

cobalt cobalt.

copper copper.

nickel nickel.

a.r.s.enic a.r.s.enic.

bis.m.u.th bis.m.u.th.

mercury mercury.

antimony antimony.

silver silver.

gold gold.

platina platina.

Argill argill.

[Note A: The above affinities were determined by Messrs de Morveau and EloI Boursier de Clervaux. These combinations were entirely unknown till lately.--A.]

SECT. XXIX.--_Observations upon Pyro-lignous Acid, and its Combinations._

The ancient chemists observed that most of the woods, especially the more heavy and compact ones, gave out a particular acid spirit, by distillation, in a naked fire; but, before Mr Goetling, who gives an account of his experiments upon this subject in Crell's Chemical Journal for 1779, no one had ever made any inquiry into its nature and properties. This acid appears to be the same, whatever be the wood it is procured from. When first distilled, it is of a brown colour, and considerably impregnated with charcoal and oil; it is purified from these by a second distillation. The pyro-lignous radical is chiefly composed of hydrogen and charcoal.

SECT. x.x.x.--_Observations upon Pyro-tartarous Acid, and its Combinations with the Salifiable Bases[46]._

The name of _Pyro-tartarous acid_ is given to a dilute empyreumatic acid obtained from purified acidulous tartarite of potash by distillation in a naked fire. To obtain it, let a retort be half filled with powdered tartar, adapt a tubulated recipient, having a bent tube communicating with a bell-gla.s.s in a pneumato-chemical apparatus; by gradually raising the fire under the retort, we obtain the pyro-tartarous acid mixed with oil, which is separated by means of a funnel. A vast quant.i.ty of carbonic acid gas is disengaged during the distillation. The acid obtained by the above process is much contaminated with oil, which ought to be separated from it. Some authors advise to do this by a second distillation; but the Dijon academicians inform us, that this is attended with great danger from explosions which take place during the process.