1. (Ph. L. 1836,—Scheele’s process.) Take of lemon juice 4 pints; prepared chalk, 41⁄2 oz.; diluted sulphuric acid, 271⁄2 fl. oz.; distilled water, 2 pints. Add the chalk by degrees to the lemon juice, made hot, and mix well; set by, that the powder may subside, and afterwards pour off the supernatant liquor. Wash the precipitated citrate of lime frequently with warm water; then pour upon it the diluted sulphuric acid, mixed with the distilled water, and boil the whole for 15 minutes in glass, stoneware, or lead; press the mixture strongly through a linen cloth, and filter it. Evaporate the filtered liquor with a gentle heat, and set it aside, that crystals may form. To obtain the crystals pure, dissolve them in water a second and a third time; filter each solution, evaporate, and set it apart to crystallise.
2. (Ph. L. 1851.) Merely placed in the materia medica.
3. (Ph. E. 1841.) Similar to that of Ph. L. 1836, except that the washed citrate of lime is ordered to be squeezed in a powerful press, and that the filtered solution of citric acid is ordered to be tested with nitrate of baryta, and if the precipitate is not nearly all soluble in nitric acid, to add a little citrate of lime to the whole liquor, till it stands this test.
4. (Ph. D. 1826.) Same as that of Ph. L. 1836.
5. (Ph. D. 1851.) Included in the materia medica.
6. (P. B. 1867.) Differs from the process of the Ph. L. 1836 in some unimportant detail only.
7. (Dr Price.) The crude juice is saturated with ammonia, potassa, or soda (carbonates), or with the ammoniacal product distilled from gas-liquor; chalk, 150 parts, or hydrate of lime, 90 parts, are then added for every 192 parts of citric acid contained in the liquor, and the whole stirred well together; heat is next applied, and the ammonia distilled into another quantity of lemon juice; the citrate of lime thus obtained is then decomposed with dilute sulphuric acid, and the whole process conducted as before. When potassa or soda is used the distillation is omitted, and the expressed liquor, after filtration, used to decompose fresh lemon juice.
8. (Ordinary manufacturing process.) To crude lemon or lime juice, mixed with water, is added ground chalk; the precipitate is washed to free it from the impurities dissolved in the water, and afterwards decomposed by sulphuric acid. If the citric acid is not sufficiently white, it is decolorised by digestion with animal black.
9. (Kuhlman.) This chemist proposes saturating the hot lemon juice as far as possible with very finely divided barium carbonate, and afterwards completing the neutralisation with barium hydrate or sulphide. The precipitated barium citrate is then to be washed, and decomposed with the requisite quantity of sulphuric acid. The advantage of barium over lime as a precipitant is the more ready crystallisability of the citric acid from the solution thus obtained. Sulphate of baryta is absolutely insoluble in solution of citric acid, whilst sulphate of lime is not; and the presence of the latter impedes the crystallisation of the acid.
Obs. If the lemon or lime juice be allowed to ferment a short time, the mucilage and other impurities will, to a certain extent, separate and subside. See Concluding Remarks.