In a copper or iron kettle of 4-l. capacity is placed a solution of 200 g. (1.33 moles) of d-tartaric acid and 700 g. of sodium hydroxide in 1400 cc. of water. A 12-l. flask through which cold water is run is placed in the mouth of the kettle in order to prevent loss of water vapor, and the mixture is boiled gently over an open flame for four hours. The solution is now transferred to a 12-l. flask or crock and partially neutralized with 1400 cc. of commercial hydrochloric acid (sp. gr. 1.19). To the still alkaline solution is now added just enough sodium sulfide to precipitate all the iron or copper which has been dissolved from the kettle (Note 1). The filtered solution is then just acidified with hydrochloric acid, boiled to expel all hydrogen sulfide, and made very faintly alkaline to phenolphthalein with sodium hydroxide solution. To the hot solution is then added a concentrated solution of 300 g. of anhydrous calcium chloride which causes an immediate precipitation of calcium dl-tartrate and meso-tartrate.

The mixture is allowed to stand for one week (Note 2) and the precipitate filtered, washed with cold water until free of chlorides, and dried at 40–50°. The yield is 246–315 g. The product is found on analysis to consist principally of the tetrahydrate, C₄H₄O₆Ca·4H₂O (Note 3). It is suspended in 800 cc. of water and treated with the calculated quantity (0.4 g. for every 1.0 g.) of concentrated (95–96 per cent) sulfuric acid. The mixture is warmed on the steam bath, with occasional shaking, or mechanical stirring, for thirty to forty hours (Note 4), filtered hot, and the calcium sulfate washed well with hot distilled water.

The united filtrate is evaporated on the steam bath until the volume amounts to 200 cc., at which point crystals should have already begun to separate from the hot solution. After standing at room temperature for twenty-four hours or longer, the crystals are filtered by suction as free from mother liquor as possible and recrystallized from an equal weight of distilled water (Note 5). The filtrate from this recrystallization is evaporated on the steam bath and the second crop of dl-tartaric acid filtered and recrystallized as before. The yield is 65–75 g. (29–33.4 per cent of the theoretical amount).

The sirupy filtrate from the dl-tartaric acid, which consists principally of meso-tartaric acid together with a small amount of unchanged d-tartaric acid, is diluted with its own volume of water and divided into two equal parts; one part is exactly neutralized with potassium hydroxide, using phenolphthalein, and the second part is added. After standing for twenty-four hours the potassium hydrogen d-tartrate is filtered off. The filtrate is neutralized with ammonia, then just acidified with acetic acid, and treated with an excess of calcium chloride solution (about 500 cc. of a 25 per cent solution). After standing for a week (Note 2) the precipitated calcium meso-tartrate is filtered and washed with cold distilled water. It may, if desired, be recrystallized from boiling water. The yield is 42–55 g. (corresponding to 13–17 per cent of the original d-tartaric acid). The sirupy free acid may be prepared from this salt by treatment with sulfuric acid as above.