Chap. III. Alkalies and Alkaline Salts.
341
be evaporated in the same manner, so as again to affordcrystals on being set aside.
Subcarbonate of potass is easily saturated with carbonicacid,, by exposing it, in solution, to the contact of the air fora considerable time, or more quickly by making a stream ofcarbonic acid gas evolved from carbonate of lime by sulphu-ric acid, pass through a solution of it, or by distilling it withcarbonate of ammonia, as proposed by Berthollet, and direct-ed by the London college. The last is more expensive thanthe second, but it does not require any particular apparatus.M. Curadow has invented a cheaper mode of saturating po-tass with carbonic acid. He dissolves the potass in a suffi-cient quantity of boiling water, mixes it with as much driedtanners' bark as to make it pretty dry, and then exposes themixture, in a covered crucible, to the heat of a reverberatoryfurnace for half an hour. By lixiviation and crystallization,the mixture affords beautiful permanent crystals of carbonateof potass. In this state it consists of about 43 acid, 40 potass,and 17 water. The saturation with carbonic acid is one ofthe best means of purifying the subcarbonate of potass; forit always separates silica from the uncombined alkali; andhence, perhaps, the employment of the subcarbonate fromtartar is unnecessarily expensive.
Liquor potass^: subcarbonatis. Lond.Solutioti of Subcarbonate of Fotass.
Take of
Subcarbonale of potass, one pound ;
Distilled water, twelve fluidounces.Dissolve the subcarbonate of potass in the water, and filter
through paper.
Aqua subcarbonatis kali. Dub.Solution of Subcarbonate of Kali.
Take of
Subcarbonate of kali, any quantity.
Place it in a wide glass funnel, whose throat is obstructedwith a rag. Set this in a cellar, that the salt may deli-quesce in the moist air. Let the solution be caught in avessel placed under it.
The preparation of the Dublin college k the old Oleumtartari per deliquium, and is a solution of carbonate of potassina variable quantity of water; for, by exposure to the air,