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 quantity 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 quantity 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 Hassenfratz, that azote enters into the composition of the tartarous radical, even in considerable quantity. 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 Rochell.
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 acetite 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 acetite 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 circumstance, 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 acetite 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. | ||
| arsenic | arsenic. | ||
| 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.]