18. Gun-cotton as a Filter

18.    Gun-cotton as a Filter. Gun-cotton, carefully prepared, is scarcely acted on by the most energetic chemical agents at ordinary temperatures. It may therefore be used as a filter for solutions containing strong acids, alkalies, etc.

19. Fusion

19.    Fusion. Aqueous fusion is the dissolving of crystalline compounds in their own water of crystallization, by the application of

heat. Igneous fusion is a term applied to the liquefaction of bodies by heat alone. The containing vessels used for igneous fusion should be of a material capable of sustaining the requisite degree of heat without either melting or cracking. Crucibles made of very refractory clay are used for high temperatures, metallic or earthenware vessels for lower degrees of heat.

20. Granulation

20.      Granulation. The reduction of metals into grains, drops, or coarse powder. This is done by pouring them, in the melted state, into water. The same effect is obtained by violently agitating the molten metal until cool, in a wooden box, well chalked inside. (See No. 25 (Pulverization).) In many cases the metal is allowed to run through the holes of a kind of colander or sieve to produce minute division; if the drops are allowed to fall from a sufficient height, they will become spherical; in this way lead shot is made.

21. Liquation

21.    Liquation. The process of sweating out, by heat, the more fusible metals of an alloy.

22. Liquefaction

22.    Liquefaction. The conversion of a solid into the Liquid state, either by heat -fusion, (see No. 19 (Fusion)); absorption of water from the air - deliquescence; or the action of a fluid body - solution. (See No. 29 (Solution).) The liquefaction of gases and vapors is effected by pressure and cold.

23. Lixiviation

23.    Lixiviation. The process of disolv-ing out or extracting the saline matter of bodies, more especially of ashes, etc., by means of ablution or digestion in water. The solution so obtained is called a lye or lixivium, and the salts resulting from the evaporation of such solutions, lixivial salts.

24. Precipitation

24.    Precipitation. This is the method for obtaining solid matter, by mixing two or more solutions of substances containing certain elementary equivalents which have a strong mutual chemical affinity. That fluid which is added to another to produce precipitation is called the precipitant. If a solution is to be precipitated, it is best, unless otherwise directed, to first heat it by means of a sand bath. (See No. 4 (Sand Bath).) A tall bell-shaped glass with a mouth is the best for precipitating. The precipitant is to bo added gradually, stirring the mixture continually with a glass rod, until precipitation ceases. The liquid should then be allowed to settle until clear. In order to ascertain whether there is any matter left in the liquid unprecipitated, let one drop of the precipitant fall into the mixture ; if any signs of precipitation ensue, more must be added; if the mixture remains unchanged and clear, the operation is complete. The liquid may then be carefully decanted and the precipitated matter, which is called a precipitate, filtered and dried. When the precipitate is the chief object of the process, it is usually necessary to wash it after filtration. This operation requires but little attention when the precipitate is insoluble in water; but when it is in some degree soluble in that liquid, great attention is required to prevent the loss which might result from the use of too much water. Precipitates soluble in water, but insoluble in alcohol, are frequently, on a small scale, washed with spirit more or less concentrated. (See No. 14 (Elutriation).)