Acids. - The citric acid is a concrete juice obtained principally from lemons : it has also been discovered in the red whortleberry, cranberry, bird-cherry, as well as in the fruits of the woody nightshade, and the dog-rose.
In order to divest this acid of the mucilaginous or other foreign particles, with which it is frequently combined, the juice obtained by pressure from lemons, or similar fruit, should first be heated, then strained, filtred, and afterwards saturated with pulverized chalk, or the carbonate of lime, till all effer-vescence cease. The precipitate, formed by this process, is called sitrate of lime; and, being insoluble, it must be separated from the liquor, washed with cold water till it become tasteless and perfectly white : next, it ought to be decomposed in a gentle heat, by adding half its weight of sulphuric acid diluted with six parts of water. As soon as the mixture becomes cool, it should be filtred; when the pure citric acid will be disengaged from the sulphate of lime. - Such acid may also be obtained in a crystalline form, by previously filtering, and then evaporating it to the consistence of a clear syrup, which concretes on exposing it to a cold temperature.
Dr. Brugnatelli has Lately published a new method of preserving and concentrating the acid of lemons. He directs the newly expressed juice to be strained through fine linen, a small portion of rectified spirit of wine to be added, and the whole to be deposited for several days in a bottle closely stopped: thus, a considerable mucilaginous sediment will be formed, but which may be easily separated, by passing the liquor through blotting - paper. If the quantity of spirit employed be considerable, it may be drawn off by distillation in a glass retort: in the contrary case, the juice may be exposed for some time in a warm temperature, and the alkohol will readily evaporate, leaving a very clear acid of peculiar strength.
The citric acid affords an agreeable lemonade, by dissolving half a dram in two pints of water; adding a sufficient quantity of sugar, and bitter-sweet, which is prepared by nibbing the latter substance on fresh lemon-peels, till the essential oil be absorbed.