There is no very delicate test for tartaric acid. Its presence in a moderately strong solution may be detected by the addition of acetate of potash, when a sparingly soluble bitartrate is soon separated, especially if the mixture be well stirred. All the tartrates on charring emit a peculiar odor resembling that of burned sugar.
A remarkable metameric modification of tartaric acid is known as racemic or paratar taric acid, 2HO,C8na0,0 2Aq. It is a frequent associate of tartaric acid, but is especially abundant in the grapes of the Vosges district. While in most respects it exhibits a close resemblance to tartaric acid (the two acids having the same composition, yielding, when exposed to heat, the same products, and their salts corresponding in the closest manner), it may be distinguished and separated from it by the following points of difference. It crystallizes more readily from solution; it contains two equivalents of water of crystallization; it is less soluble in alcohol; and the racemate of lime is soluble in hydrochloric acid, and is precipitated unchanged on adding ammonia. Its most important difference, however, is, that its solution does not rotate the plane of polariza tion, while a solution of ordinary tartaric acid exerts a well-marked right-handed rota tion.
The brilliant researches of M. Pasteur on the optical and chemical properties of tar taric and racemic acids, have opened up a new and most important field of investigation in relation to the molecular composition of organic bodies. We shall give the briefest possible abstract of his remarkable discoveries, and must refer for fuller information to his numerons,ineinoirs in the Comptes Rendus, Annales de (Abide, and other French scientific journals. He has proved that racemic acid is a mixture of ordinary tartaric acid (to which, from its optical property, he applies the term dextro-racemic acid) and of an acid which produces left-handed rotation, to which he gives the name laco-racemic acid. (These acids arc also known as dextro-tartaric and taco-tartaric acids.) He found that, by saturating racemic acid with soda and ammonia, and allowing this solution to crystallize slowly, two varieties of crystals are obtained, which may be distinguished by their form, in the same way as the image and the reflection of the image in a mirror differ; or as right-handed and left-handed. If the two kinds of crystals are separated, and then dissolved, each solution is found to act powerfully'on polarized light, but in opposite directions. On separating these acids from their bases, and mixing equal parts of concentrated solutions of each, racemic acid is again formed, which exerts no action on a polarized ray. M. Pasteur has subsequently made the discovery, that racemic acid may be artificially produced by the action of heat upon certain compounds of tartaric acid (such as tartrate of cinchonine or tartaric ether), which are capable of resisting a high temperature. The formation of racemic acid in this way is accompanied by the produc tion of another modification of tartaric acid, which he calls inactive tartaric acid, which, like racemic acid, has no action on polarized light, but unlike it, cannot be resolved into dextro and lffivo-racemic acids.
Tartaric acid and the tartrates. in their relation to medicine, are of considerable im portance. Pure tartaric acid, in small doses diluted largely with water, forms a good refrigerant drink in febrile and inflammatory affections, and is much employed for this purpose in hospitals, etc., as being cheaper than citric acid. It has been stated that persons addicted to habitual drunkenness have been reclaimed by the following treat ment: A few crystals of the acid are dissolved in two small tumblers of water, and taken in the morning fasting, an hour intervening between the tumblers. The painful feeling of sinking and craving of the stomach, of which such persons usually complain, is said to be removed by these acid draughts. Under the name of acidulated drops, lozenges composed of this acid, sugar, and oil of lemons are largely employed in mild sore throats and colds. The principal medical use, however, of tartaric acid is in the preparation of effervescent draughts, when added to alkaline carbonates; and in the composition of seidlitz powders (q.v.). Tartrate of potash is a mild but efficient purga tive in doses of from two to six drams, which is perhaps hardly so mue'i used as it deserves. In passing through the system it becomes converted into carbonate, and thus renders the urine alkaline. Acid tartrate, or bitartrate of potash, commonly kkown as cream of tartar, in full doses, acts as a sharp purgative, but is generally prescribed with some of the milder vegetable cathartics. When administered in small repeated doses from a scruple to a dram), in a large quantity of water, it largely increases the secretion of urine, and is consequently of great service in dropsy. It may be agreeably given in either of the following forms: (1) Imperial, which is prepared by dissolving a dram of cream of tartar in a pint of boiling water, and flavoring with lemon-peel and sugar. In incipient dropsy, a couple of tumblers of this mixture, with half a glass of good hollands in each, are strongly recommended by Dr. Neligan as an after-dinner drink. The pro portion of cream of tartar to the pint of water may be gradually increased to two drams. (2) Cream of tartar whey is prepared by boiling 100 grains of the salt in a pint of new milk, and removing the curds by straining. Either of these drinks may be safely taken to any extent agreeable to the patient. Tartrate of iron and potash, the ferrum tartara tum, or tartarated iron, of the pharmacopccia, is a mild chalybeate tonic, which, in consequence of its somewhat sweet taste, is well adapted for children. It occurs in transparent scales of a deep garnet color, is soluble in water, and sparingly soluble in spirit. The dose varies from 5 grains to a scruple, three times a day, either given with
honey or treacle, or dissolved in some aromm.c water. The wine of iron (vinum ferri of the Pharm. Brit.) consists of sherry with tartratcd iron in solution. Each dram ought „, to contain one grain of the salt. The tartrate of iron and ammonia, or ammonio-tartrate of iron, closely resembles in its action the tartrate of iron and potash. Although not in the Pharm. Brit., it is "an excellent preparation of iron, void of all astringency. Its not disagreeable taste, its solubility in water, its compatibility with the alkaline car bonates, and the permanency of its composition, give it an advantage, over most of the other preparations of iron. It is peculiarly suited as a tonic for those derangements of the uterine organs in which ferruginous salts are indicated,"—Neligan's Medicines, 6th ed. p. 645. The dose is from 5 to 8 grains, and it may be prescribed in the form of powders, pills, or solution; or made into a bolus with honey. Tartar emetic, in doses of from A to of a grain, frequently repeated, acts as a diaphoretic or sudorific; nausea sometimes accompanies the diaphoresis, but it has the advantage of increasing the tendency to perspiration. The addition of the compound tincture of lavender tends to prevent the supervention of vomiting. Tartar emetic in these small doses is of great service in febrile disorders, in the hmoptysis of phthisis, is obstinate cutaneous dis eases, etc. Antimonial wine consists of sherry holding tartar emetic in solution in the proportion of two grains to the ounce. The dose, to produce a diaphoretic action is 20 or 30 minims every hour. If we require an expectorant action—as in acute pneumonia or bronchitis—the salt should be given in still smaller doses, as from to A of a grain. Tartar emetic, in doses of two or three grains, dissolved in water, acts as a pow erful emetic, and at the same time produces much nausea and depression, and not un frequently purging. The vomiting seldom occurs till about 20 minutes after the draught has been taken If tartar emetic is thus given at the commencement of febrile or inflammatory affections, it will often cut short the impending disease. With this view it is employed in continued fever, croup, whooping-cough, etc. It used to be given to relax the muscular system, in cases of strangulated hernia and dislocation; but chlo roform is far better for these objects. In cases of poisoning it is inferior to sulphate of zinc. It is expedient to take the emetic dose in parts, as too powerful an effect is thus prevented. Two grains, which are generally sufficient, must be dissolved in eight ounces of water, of which a quarter should be taken every ten minutes till vomiting ensues. The patient should walk gently about his room between the doses: If a large dose (of one, two, or even three grains) be repeated every second hour, the nausea, vomiting, and purging (which often follows a full dose) cease after two or three such doses, and the main action seems to be exerted in depressing the circulation and lower ing the pulse. Hence, tartar emetic given in this way is a direct sedative or contra stimulant, and is of great service in pneumonia and pleurisy. "As a contra-stimulant," says Neligan, "tartar emetic is given in doses of from half a grain to two grains every hour or second hour, dissolved in one or at most two ounces of orange-flower water. The first dose or two should not exceed half a grain, and the patient should not be per mitted to drink, so as, if possible, to avoid the production of vomiting. When once a tolerance of the medicine is produced in the system, the quantity taken may be rapidly increased."—Op. cit., p. 418. Lastly, tartar emetic, when applied to the skin, produces a crop of pustules, which ulcerate, and discharge purulent matter. In consequence of this property, tartar emetic, either in the form of ointment or of saturated solution, is often employed as a counter-irritant in various affections of the viscera of the chest and abdomen, in diseases of the joints, etc. The ointment is applied by rubbing about half a dram on the skin night and morning. In two or three days pustules begin to appear, when the further application of the ointment should be temporarily suspended. The saturated solution is a cleaner preparation than the ointment, and acts more speedily. It is applied by means of pledgets of lint soaked in it. Tartar emetic, in excessive doses, or in small repeated doses, acts as an irritant poison. Dr. Taylor has reported 37 cases of poisoning by this agent, of which 16 were fatal. The smallest fatal dose was in a child three-quarters of a grain, and in an adult two grains, but in the last case there were circumstances which favored the fatal action of the poison. The symptoms occurring in chronic poisoning by this salt are "great nausea, vomiting of mucus and liquids, great depression, watery purging, followed often by constipation of the bowels, small, contracted, and frequent pulse, loss of voice and muscular strength, coldness of the skin, with clammy perspiration, and death from complete exhaustion." A considerable num ber of cases are on record in this country in which murder has been perpetrated by the slow action of tartar emetic. The most important of them are referred to by Dr. Taylor in his Xedical Jurisprudence, pp. 146 and 250, to which must be added the Pritchard case in Glasgow, 1865. The Pharmaceutical Journal for Oct., 1865, contains direc tioas, by Messrs. T. and H. Smith, of Edinburgh, for an antidote to be pre scribed after a large dose of tartar emetic has been taken. The ingredients are solution of perchloride of iron and calcined magnesia.