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 quantity 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. | ||
| arsenic | arsenic. | ||
| bismuth | bismuth. | ||
| 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. XXX.—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-glass 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 quantity 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.