Tartarised ammonia seems not to have been examined: it certainly has not been employed as a medicine. Its crystals are tetraedral pyramids, with obliquely truncated summits.

Borax is a natural production, which nature offers, partly saturated with soda, as the acid of tartar is with kali. The crystals of borax are hexangular prisms; of which two sides are broader than the others, terminated by white triangular pyramids. The taste is styptic and urinous; it colours vegetable blues green, is soluble in 18 parts of cold water, and in 6 of boiling. It slightly effloresces in the air, swells with the loss of nearly half its weight from heat, and becomes a porous friable mass, melting in a greater heat to glass. It is decomposed by all acids and alkalis, by the sulphats, nitrats, muriats, phosphats, and fluats, of all the earths, and of ammonia. The boracic acid forms 39 parts, soda 17, and water 44.

Its acid was styled by Homberg, who discovered it, the sedative salt, from its supposed soothing power in fevers. It appears in small, shining, laminated crystals, and its specific gravity is 148. It vitrifies in the fire; is soluble in water and alcohol, imparting to the latter the property of burning with a yellow flame. Of borax we have already spoken; but of the borats we know little, and they certainly form no part of the materia medica.

The citric and oxalic acid are employed in medicine; but their compounds, the citrats and the oxalats, except in one uistance, the citras potassae, do not claim the physician's attention. We must not, however, wholly omit them or the other acids, as in the rage for novelty they may in turn share our regard.

The acid of lemons is with difficulty separated from its mucilage, so as to be reduced to the state of a limpid solution or a crystalline form. Various attempts have been made to concenter it by freezing, or to combine it with spirit of wine, from which the mucilage is easily separated. The most successful plan was suggested by Scheele, to combine the acid with chalk; from which, as the salt is nearly insoluble, the mucilage may be readily washed: the citric acid is then separated by adding the sulphuric. It is one of the strongest of the native acids; and cannot, like the greater number of the others, be converted into the oxalic by means of the nitric acid. Its crystals are octoedral prisms, truncated on their solid angles. The citric acid unites with alkalis, earths, and even metals. With the fixed alkali it is supposed to sit more easily in the stomach than any-other neutral; which, if true, may be owing to some remains of the carbonic acid gas separated from the alkali, and entangled in the fluid: but all neutrals possess, in a certain degree, an anti-emetic power. The citric acid decomposes all tartarised neutrals.

The malic acid is not peculiar to apples, from whence its name is derived, but is found in all unripe fruits, and may be converted into oxalic acid by the nitric. It is separated from the mucilage by combining it with chalk, and then adding the acetite of lead. The ma-late of lead thus formed is decomposed by the sulphuric acids. This acid is frequent in a variety of plants, particularly the succulent ones, and in common parsley: and Vauquelin tells us, that when the juice of a plant furnishes a copious precipitate with oxalate of ammonia, and a flocculent one with acetite of lead, it undoubtedly contains a malate of lime. By fire, this acid is destroyed or converted into carbonic acid. The ma-lates of alkalis are deliquescent, but the malate of alumine is with difficulty soluble: it unites with iron and zinc: the chalybeate salt does not crystallize; that with zinc forms fine crystals.

The oxalic acid which nature offers us combined like tartar, in part with an alkali, has a penetrating sour taste. It effloresces in the air; and is soluble in twice its weight of cold, and half its weight of boiling, water. Like all the weaker acids, it dissolves the metallic oxides rather than the metals themselves; and it combines with the more common earths. With lime it forms a salt so insoluble, that it becomes the surest test of calcareous earths and its compounds; though Brugnatelli suspects its infallibility.

The acid of sugar is one of those products from the vegetable oxides by means of the nitric acid which we have already mentioned. Not only sugar, but mucilages, mild oils, and flour, assume by this intermede the form of an acid; and this acid is invariably the oxalic.

The gallic acid seems to collect its oxygen from the air, since long exposure to the atmosphere is necessary to its production. The taste is acid and astringent; it effervesces with lime, and reddens the blue vegetable infusions. The salt requires twelve tunes the quantity of cold water, and one and a half of warm. It dissolves also in alcohol, in equal quantities when hot, but requires four times its weight when cold. It forms oxalic with nitrous acid; and the acid, when sublimed. 3H resembles in obvious qualities the benzoic. The gallic acid is totally distinct from the tanning principle; with which, as both are often united, it has been confounded.

The acid of cork is sharply acid and bitter. It deliquesces in the air, and becomes brown by the sun's light. It is distinguished from the acid of camphor, by turning the solution of indigo green; from the gallic acid, by its yellow precipitation; and from the malic, by its solid form. It does not burn or smoke on hot coals, like the tartarous; gives a green hue to a solution of nitrat of copper, without occasioning any precipitation; and does not attract lime so strongly as the oxalic acid.

The benzoic acid appears very generally in the vegetable chemistry; and we have mentioned it as the acid which gives the balsams their distinguishing properties. Since that article was printed we have received Mr. Hatchett's valuable observations on this and some other acids; and we have thus a striking proof, if any other "was wanted, of the utility of frequently returning to the same subject in a progressive work like the present, if we would, as we profess, render it a picture of the science at the present moment. The properties of the benzoic acid, as generally recognised, occur under the article Benzoinum. We must now add, however, the formula adopted in the last edition of the Edinburgh, from the Prussian, Pharmacopoeia; not as a chemical refinement only, but as better fitting it for being reduced to a powder, should it be ever employed as a medicine. Twenty-four ounces of gum benjamin are triturated with eight quarts of water for half an hour; the water is strained off, and the gum again triturated with three quarts of water and strained. The strained liquors are mixed and evaporated to a quart, to which diluted sulphuric acid is gradually added while any precipitation appears. The precipitated acid is dissolved in boiling water, strained while hot, and set aside to crystallize. The crystals, which are. less beautiful than the flowers, must be washed in cold water, and preserved in a dry phial.