Prunes, Pulp of. Syn. Prepared prunes; Pulpa prunorum, Prunum præparatum (Ph. L.), L. Prep. The imported dried fruit is boiled gently for four hours with water, q. s.
to cover them, and then pressed, first through a fine cane sieve, and afterwards through a fine hair sieve; the pulp is, lastly, evaporated by the heat of a water bath to the consistence of a confection. A better plan is to use as little water as possible, by which the necessity of subsequent evaporation is avoided. Used in the preparation of confection of senna.
PRU′NING varies according to the kind of plant or tree operated on and the particular object in view, and its skilful performance must, therefore, greatly depend on the experience and knowledge of the gardener. “In the operation of pruning, the shoots are cut off close to the buds, or at a distance not greater than the diameter of the branch to be cut off; because without the near proximity of a bud the wounds will not heal over. In shoots which produce their buds alternately the cut is made at the back of the bud sloping from it, so that it may be readily covered by the bark in the same or in the following year; but in the case of branches where the buds are produced opposite each other, either one bud must be sacrificed or the branch must be cut off at right angles to its line of direction, which is most conveniently done with the pruning shears.” (Loudon.)
PRUS′SIAN AL′KALI. Ferrocyanide of potassium.
PRUS′SIAN BLUE. Syn. Berlin blue, Paris b., Ferrocyanide of iron, Prussiate of i., Cyanuret of i. This is the well-known blue pigment of the shops.
Prep. 1. The crude but clear solution of ferrocyanide of potassium (blood lye) is precipitated by a mixed solution of alum, 2 parts, and green sulphate of iron, 1 part; the dingy greenish precipitate that falls gradually becomes blue by absorption of atmospheric oxygen, which is promoted by exposure and agitation of the liquor; as soon as it has acquired its full colour, the sediment is repeatedly washed with water, and is then drained, and dried, at first in a stove, but afterwards on chalk stones. Product large, but inferior in quality.
2. Repeatedly digest and wash the precipitate obtained by the above process in very dilute hydrochloric acid, and then in pure water; drain and dry it, as before. Superior.
3. (Paris blue.)—a. Neutralise the solution of ferrocyanide of potassium (blood lye) with dilute sulphuric acid, precipitate the liquid with a solution of any persalt or sesquisalt of iron (as the persulphate, nitrate, sesquichloride, or peracetate); well wash the precipitate with water, and dry it, as before. A very rich and intense colour.
b. (Hochstätter.) Crystallised ferrocyanide of potassium and green sulphate of iron, of each 6 parts, are each separately dissolved in water, 15 parts; after the admixture of the solutions, and frequent agitation, oil of vitriol, 1 part, and fuming hydrochloric acid, 24 parts, are stirred in; after some hours have elapsed a
strained solution of chloride of lime, 1 part, dissolved in water, 80 parts, is gradually added, the addition being stopped as soon as an effervescence from the escape of chlorine is perceived; the whole is now left for 5 or 6 hours, when the precipitate is thoroughly washed in pure soft water, drained, and dried. Or, instead of the above, the precipitate is at once washed in dilute nitric acid until its colour ceases to be improved by the process. The product is of the finest quality.