Home › Manipulations › Precipitation

Precipitation

This is the method stances it holds in suspension. The most for obtaining solid matter, by mixing two or efficient filter is produced when the first two more solutions of substances containing cerare so graduated to the latter, that the liquid tain elementary equivalents which have a filters rapidly and is rendered perfectly trans- strong mutual chemical affinity. That fluid parent. (See No. 3838.) (Cooley.) which is added to another to produce precipi-

Tinctures and dilute spirits are usually tation is called the precipitant. If a solution filtered through bibulous paper placed on a is to be precipitated, it is best, unless otherfunnel, or through thin and fine cotton bags. wise directed, to first heat it by means of a In general, tinctures clarify themselves by the sand bath. (See No. 4.) A tall bell-shaped subsidence of the suspended matter, when alglass with a mouth is the best for precipitatlowed to repose for a few days. Hence it is ing. The precipitant is to be added gradually, the bottoms alone that require filtering; the stirring the mixture continually with a glass supernatant clear portion need only be run rod, until precipitation ceases. through a small hair sieve, a piece of tow or should then be allowed to settle until clear. The liquid cotton placed in the throat of a funnel, or In order to ascertain whether there is any some other coarse medium, to remove any matter left in the liquid unprecipitated, let floating substances, as pieces of straw, &c.

Spirits largely loaded with essential oil, as those of aniseed, &c., run rapidly through paper or muslin, but usually require the addition of a spoonful or two of magnesia before they will flow quite clear. When possible, tinctures, spirits, and all similar volatile fluids, are better cleared by subsidence or clarification than by filtration, as, in the latter way, part is lost by evaporation. (See Nos. 3834, &c.)