Tartaric Acid

The mode of using the apparatus 'is as follows. The tartrate compound being run into the decomposing tank, the liquid becomes entirely separated by virtue of the filtering medium, to be treated as circumstances may require. Cold water is then allowed to percolate through the mass until it has removed from it all impurities, when it is fit for decomposition by means of sulphuric acid, for which purpose (the outlet being closed), as much washing from a previous operation is added to the partly dry mass as is necessary to make it semi-fluid, and also some mother liquor of a previous working in order to extract from the latter the excess of sulphuric acid which it has gained from frequent concentration, and then as much more sulphuric acid as may be required to complete the decomposition and liberate the tartaric acid, and show a slight reaction with a soluble salt of lime, the stirrers being meanwhile kept in motion. A complete admixture of the contents of the tank being thus effected, the outlet pipe is then again opened and the liquor run into a suitable reservoir, the remaining sul phate of lime or other base being washed clean with water in the ordinary way, the weaker washings being kept for future operations. The results are that the colouring matter and the iron contained in the tartar under treatment are effectually removed, and the tartrate of lime or other base is washed more com pletely, and thereby rendered less liable to fermentation than when washed by the ordinary means, while the solution of tartaric acid is produced in a much purer and more concentrated state, thus effecting a great saving in the expense of evaporation and recrystallization.

Messrs. Dietrich and Schnitzer propose a plan for removing the inconveniences attending the separation of the tartaric salts contained in wine residues, due to the mucilaginous properties of the accompanying impurities, which is substantially as follows.

The residues arc heated according to their nature and to the means employed, for a greater or less time to a temperature of about 129° (284° F.) to 170° (338° F.). This heating causes the foreign matters partly to_become insoluble and partly to be transformed into a condition in which they no longer offer any difficulty in separation. The heating may be conducted in a variety of ways : In closed or open vessels by means of an ordinary open fire, or by hot baths, or by steam either superheated or under pressure ; but it is perhaps preferable to heat the residues in a dry state, when possible, and when it is not possible to render them dry, closed vessels are best, in whioh the heating is effected by direct steam. Hitherto, in the manufacture of tartarie acid from tartar (bitartrate of potassa), the acid alone is separated, and the potassium of the tartar remains, and can by several combinations be obtained as an accessory product, but the attempts which have often been made to obtain this potassium in a valuable form are without a fair result.

Tho following method of manufacture, due to Franz Dietrich, a Soo ins chemist, indicates deeiL•d improvements. If tartar (bitartrate of potash) be treated by a surplus of carbonate of lime and water, these substances are decomposed, as shown by the following equation :— (a) — 188.1 bitartrate of potash = — 188•0 tartrate of lime.

— 100.0 carbonate of lime — 100.1 carbonate of potash.

284.1 But this transformation is only effected under the condition that the operation be conducted in closed vessels, and the developed carbonic acid prevented from getting out of the vessel. In conse quence thereof a pressure is produced, which hastens the reaction; this latter is effected as follows : —Owing to tartar not readily dissolving in cold water, only a small quantity of the tartar dis solves, meets the carbonate of lime in suspension, and decomposes it according to the equation i,9, namely :— — 376.2 bitartrate of potash = — 188.0 neutral tartrate of lime. — carbonate of lime — „ „ potash.

— carbonic acid.

— 18.0 water.

Tho neutral tartrate is now dissolved ; the carbonic acid prevented from escaping is also dis solved under a pressure proportionate to the size of the vessel and the quantity of the substances which have undergone the reaction. By these means carbonate of lime is dissolved with facility, and there is obtained a solution of bicarbonate of lime, which is transformed together with the neutral tartrate of potassa according to equation (9, namely :— — neutral tartrate of potash = — 188.0 neutral tartrate of lime. CAA, — 140.0 carbonate of limo — bicarbonate of potash.

— carbonic acid.

— 18.0 water.

As soon as bicarbonate of potassa has been formed, the decomposition goes on more rapidly, as the tartar can now dissolve directly in this salt according to equation (d), namely :— — bitartrato of potash = — 226.2 neutral tartrate of potash. KHOO, — 100.1 bicarbonate „ — 44.0 carbonic acid.

— water.

288.2 288.2 Tho products of this latter reaction decompose themselves together with carbonate of lime according to equation (c).

All these reactions go on one after the other, and one by the side of the other, until all the tartar has been transformed into tartrate of lime and bicarbonate of potash. Tho pressure, which at the commencement is rather low, is elevated with the energy of the action up to a maximum, is again lowered, and disappears at the end of the operation. It is a special peculiarity of this process that the carbonic acid required for the decomposition is developed by the mixed matters themselves, and that the mechanical labour necessary for getting the mixture under pressure is furnished with out expense by this same carbonic acid.