New and better methods of manufacture have to a large extent supplanted the wood process; but the industry is still a very large one. It is carried on chiefly in America, Canada, Russia, France, Italy, Poland, Belgium, and Austria ; America alone supplies about one-half of the total amount manufactured. The prices range from 20s. to 24s. per cwt. for pot-ashes, and from 28s. to 32s. for best pearl-ashes.
Carbonate of Potash from Beet-root Molasses.—The existence of considerable quantities of potassium saltfiin the juice of beet-root has been for long a recognized fact, and many processes have been set on foot for their extraction. These salts are for the most part left in the mother Honors or " molasses " of the ordinary sugar-refining process, after crystallization.
The potash salts are extracted from the molasses in the following manner : —The liquors are diluted down to about 1.05 and slightly acidified with sulphuric acid. A small quantity of the yeast of beer (2 to 21 per cent.) is added, and the whole is then allowed to ferment for a period of about five days. The spirit is then distilled off, leaving a liquor, usually called " vinasse," which contains all the original potash salts. To this an excess of chalk is added, and the resultant sulphate of lime, &c., allowed to settle. To facilitate this process, it is usual to concentrate the liquors slightly in an iron pan and then run them into tanks to aettle. The clear supernatant liquor ia siphoned off into wrought-iron pans, boiled down to dryness, and finally calcined in a reverberatory furnace. The crude product is called " salin," and contains from 35 to 45 per cent. of carbonate of potash. The effect of the lime is to notably increase the proportion of the potash salt. The composition, of course, varies very considerably with the different soils, and state of the soils, upon which the beet-root has been grown.
A very excellent furnace for calcining the vinasses is shown in Fig. 204, the construction of which will be at once appareat. The sole of the furnace is divided into two compartments. The liquors are kept in a small bath placed upon the arch, and a portion is run down, as may be required, into a suitable vessel placed upon the bed of the compartment farthest from the fire, to which vessel ia attached a long handle to move it forward. As soon as the contenta
of this ladle assume a thick, pasty consistency, they are removed to the compartment next the fire, where calcination is completed. In tbe meantime the ladle ia drawn back and refilled with another charge of liquors.
A refined product has of late years come into favour. This is produced either by washing the crude " salin " with water, and boiling down and cakioing the resultant liquors, or by cryatallizing out as far as possible all impuritiea.
Or, to obtain a still better carbonate, the " salin " is washed, and the lixivium concentrated up to 1.5. During concentration, sulphate of potassium and chloride of potassium crystallize out and are skimmed off. The mother liquors are further concentrated and run into shallow cooling pane. Here a mass of crystals— a mixture of various salts, but chiefly a double salt of carbonate of potas sium and sodium—separates out. The residual liquors are then removed, boiled down to dryness, and calcined. The crystals are dissolved and recrystallized, the mother liquor again yielding a quantity of pure potassium carbonate.
Two other processes for obtaining carbonate of potassium from molasses may be mentioned. Billet distils the " vinasses " in an ordinary gas retort, pausing the ploducts of distillation first into a small vessel where the greater part of the tar condenses, then through a worm placed in water, the products of condensation falling into a reservoir. The uncondensable gases pass off into a purifier, and may be burnt. In the retort is left a product answering to the " salin " already described. This is raked out, lixiviated, evaporated, and calcined. Seymour treats the aaccharine juices with solution of caustic baryta, or sulphide of barium, obtaining saccharate of baryta as a precipitate. This is washed with a weak solution of caustic baryta. The liquors are evaporated or subjected to a stream of carbou dioxide, to remove the baryta as hydrate or carbonate, and the residual liquors boiled down to obtain the alkaline salts.
The extraction of carbonate of potash from bect-root molasses is a rapidly increasing trade. It is carried on chiefly in France, Germany, Belgium, and Austria, and yields something like 12,000 tons per aunum.