27. Saturation

27.    Saturation. A liquid is said to be saturated with some other substance when it ceases to dissolve any more of it. An acid is saturated with an alkali when sufficient of the alkali has been added to completely neutralize the acid, and vice versa.

28. Sifting

28.    Sifting. This is a means employed to obtain uniformity of fineness in a pulverized substance; and is also of use in mixing different substances powdered to the same degree of fineness. The sieves used for this purpose are furnished with cloths of various materials and different degrees of fineness; consisting of brass wire, horse hair, buckram, book muslin, gauze, or raw silk; this last constituting a bolting cloth for sifting impalpable powders. These are stretched over a wooden cylinder in the same manner as the head of a drum. During the process of pulverizing, the use of the sieve is necessary from time to time to separate the finer powder from the coarser particles, which have to be returned after each sifting, to the mortar for further trituration. The powder is made to pass through the meshes of the sieve by gently agitating it between the hands; a rough jarring motion will force through some of the coarser particles, and destroy the uniformity of the powder. A sieve should be fitted with a drum head, top and bottom, the upper one to confine the dust of the substance being sifted, and the lower one to catch the sifted powder as it falls through the sieve. An arrangement of this kind is called a drum or box sieve.

29. Solution

29.    Solution. Under the head of solutions, are properly included only those liquids which consist of water or an aqueous menstruum, in which has been dissolved an appropriate quantity of any soluble substance to impart to the liquor its peculiar properties. When spirit is the dissolving medium, the liquid receives the name of alcoholic solution, spirit, or tincture, while substances dissolved in water form aqueous solutions. In cases where a substance is dissolved in an acid or alkaline solution, whose acid or alkali is afterwards neutralized by means of an alkali (to counteract the acid), or an acid (to destroy alkali), the solution is then termed a neutral solution. A saturated solution is a solution made according to No. 27.

Professor Youmans, in the "Hand Book of Household Science," says: " Solids should be crushed or pulverized, to expose the largest surface to the action of the solvent liquid. Substances which in the lump would remain for days undissolved, when reduced to powder are liquefied in a short time. When a solid, as common salt or alum, is placed in a vessel of water to dissolve, it rests at the bottom. The water surrounding it becomes saturated, and being heavier, remains also at the bottom, so that the solution proceeds very slowly. By stirring, the action is hastened, but this takes up much time. The best plan is to suspend the salt in a colander, basket, or coarse bag, at the surface of the liquid. As the particles of water take up the particles of salt, they become heavier and sink; other particles take their places, dissolve more of the salt, and sink in turn, so that the action of a constant current of liquid is kept up on the suspended crystals, and always at that portion most capable of dissolving them."