This acid has a sour taste and acts powerfully on vegetable colours.
400. It is used to take out ink spots. It is also one of the best tests of the presence of lime.
Exp. Dissolve some oxalic iir id in pure water and let fall a few drops of it into well water. It' the s-nallest quantity of lime be present there will be loi med a white cloud, whicn being an insoluble oxalate of lime will afterward fall to the bottom of the vessel. .
401. This acid forms with the different bases a set of salts called oxalates.
402. Tartaric acid. This acid is obtained from the Supertartrate of potash (common cream of tartar.) Cream of tartar is the lees of wine purified.
403. The casks in which some kinds of wine are kept become encrusted with a hard substance, tinged with the colouring matter of the wine, and is otherwise impure. This substance is known in commerce by the name'of argol. When this is puiified by solution, filtration, and crystallization, it is called cream, or crystals of tartari From their substance the tartaric acid is procured by'tli? following process.
Exp. Let 100 parts of finely powdered cream of tartar, be intimately mixed with about 30 parts of pulverized chalk. This is best done by grinding them in a mortar and passing the mixture through a sieve. Let the mixture be thrown by spoonfulls into eight or ten parts of boiling water: waiting Cor the cessation of the violent effervescence, which is produced by each addition, before any more is thrown in. If it should appear that the acid is not fully neutralized by the above quantity of chalk, but that the solution reddens litmus paper, more chalk must be added until the paper is not chang ed by it.
By the above operation, the tartaric acid combines with the lime, and an insoluble tartrate of lime is found at the bottom of the vessel. Decant the liquor into another vessel, and having collected the tartrate of lime, wash it three or foar times with cold water. Then to the tartrate of lime thrown into a convenient quantity of water, add strong sulphuric acid, equal in weight to that of the chalk employed. The sulphuric acid combines with the lime and forms a sulphate, which is insoluble in the water, it therefore falls to the bottom of the vessel in the form of a white powder. Let the acid and precipitate remain together twenty-four hours, frequently stirring them, then let the precipitate subside aDd decant the clear liquor, which will contain the tartaric acid in solution, together with some sulphuric acid and a small quantity of sulphate of lime. This is to be evaporated by a gentle heat, now and then decanting' it from one vessel to another to get rid of the sulphate of lime which falls down. Finally, after the solution is eva; orated to rather more than 'a fourth of the original quantity, set it away to crystallize. The crystals will be brown and must be purified by again dissolving them in water, evaporating and crystallizing, and this must be repeated until the crystals are pure, white tartaric acid.
404. In the manufactories of this article, some additional processes are used by which a larg r quantity of the-acid is obtained from the same quantity of materials, than can be obtained by the above process.
405. This acid and the carbonate of soda form the boda powders, of which great quantities are prepared
^forf gold during the hot season.
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