Page:The American Cyclopædia (1879) Volume XIII.djvu/781

 POTASH 757 it may be freed by dissolving in absolute alco- hol, evaporating, and again fusing. Hydrate of potash may be economically separated from some feldspars and micas by calcining the min- erals with lirne and leaving the products for some time in contact with water; but the sources which appear likely to supersede all others are the potash minerals, such as syl- vine, kainite, and carnallite, found in enor- mous quantities in the salt mines of Stassfurt, Germany. The explorations in one locality have developed the existence of a mass of car- nallite equal to 6,000,000 tons 'of chloride of potassium. The pure hydrate is a white solid substance, of crystalline fracture, and specific gravity 1'V. It is very deliquescent, dissolv- ing readily in water, the solution of specific gravity T68 containing 51 -2 per cent, of the alkali, and boiling at 329 F. It fuses at a low red heat, and at a white heat it vola- tilizes without separation of the water. It has an acrid taste and corrosive action upon the cuticle, dissolving and decomposing or- ganic tissues. It is one of the most power- ful bases known, and is hence largely em- ployed for decomposing saline compounds, the acids of which it seizes. It absorbs carbonic acid from the atmosphere, and must conse- quently be preserved in glass-stoppered bot- tles, and the glass of these must be free from lead. Mixed with the fat oils, it forms soaps ; and in various other ways it is a most useful article in the arts, in chemistry, and to some extent in medicine. The pharmaceutical prep- aration known as liquor potassce is a solution in water of the hydrate, of specific gravity about 1*05, and containing 4*7 per cent, of po- tassa. Its properties as an antacid, &c., are however as conveniently serviceable in the car- bonate of potash. In excessive doses its poi- sonous action is neutralized by vinegar, the milder acids, or the oils. Commercial potash, the crude carbonate and hydrate, is chiefly obtained from wood ashes, and is the princi- pal portion of the soluble matters which these contain. The alkalies that exist in the soil are derived from the decomposition of different rocks and minerals. Feldspar and mica, in- gredients of granite, are particularly prolific sources of potash and soda ; but they cannot be made to yield these alkalies so economically as the plants, which have taken them up in their sap and hold them in a soluble state, combined with oxalic and tartaric and other vegetable acids, and also with silicic and sul- phuric acids. By burning the plants, the salts of the vegetable acids are decomposed, and the potash combines with carbonic acid, remain- ing with the ashes as a carbonate. The ashes, moreover, contain as soluble ingredients car- bonate of soda, the sulphates and silicates of potash and soda, and chlorides of the metals, including chloride of potassium; and besides these, insoluble earthy matters, which are of no value in connection with the production of the alkalies. The proportion of these two. classes of ingredients varies in ashes obtained from different plants and their parts, ranging generally from T V to T 9 7 insoluble, and leaving TV to T 3 o soluble. Berthier found the soluble portion of the ashes of oak wood to amount to 12 per cent., of white beech wood 19-22 red beech 16-3, birch wood 16, fir wood 26'7 fir charcoal 50, pine wood 13-6, wheat straw 10, and potato vines 4*2; and other chemists report the ashes of bean vines to contain 33 per cent, of soluble matter, of pea vines 27*8, of rye straw 19-47, &c. The branches and bark contain more saline matter than the solid wood, a distribution perhaps dependent on the potash existing chiefly in the sap. The stalks of tobacco, potatoes, beet leaves, tansy, sorrel, &c., contain large proportions of potash, and the removal of such products every year from the soil must cause its impoverishment, unless the potash is restored in other ways. When ashes are treated with water a strongly alka- line solution is produced called a lye, and when this is drawn off and evaporated to dryness the soluble salts remain behind. The evaporation used to be conducted in iron pots, and hence the name potash. The manufacture is largely carried on in several wooded countries, espe- cially where it is desirable to clear off the for- ests for agricultural purposes ; but it appears to be northern countries alone that produce sup- plies for commerce. These are the northern American states and Canada, and Germany, Eussia, and the other countries of the north of Europe. The method pursued in the Amer- ican forests is to burn the wood in large heaps to ashes. Barrels sawed across in the middle furnish tubs, which are provided with a false bottom perforated with holes and supported upon cross sticks a little above the real bot- tom. Straw is laid upon the false bottom, under which is a cock for letting off the lye. The ashes mixed with about 7 V f ^ me are placed in the tubs and drenched with suc- cessive portions of water, which are allowed to remain for an hour or two. Those first drawn off, being saturated with the soluble salts, are conveyed directly to the evaporating pans ; but the succeeding portions, being weak, are retained to use again upon fresh ashes. The pans are of iron, broad and shallow, and with corrugated bottoms to increase the heat- ed surface. When the liquor becomes of sirupy consistence the heat is checked, and the con- tents of the pan soon solidify. These when cold are dug out with some difficulty and placed aside as crude potashes. They are intensely alkaline, and reddish brown from the carbona- ceous matter they retain. They are afterward purified by heat on the floor of a furnace, losing most of the sulphur that may be present, the excess of water, and other volatile matters, the whole loss amounting to 10 or 15 per cent. The product is white, of a bluish or pearly cast, contains a larger proportion of carbonic acid than the crude article, and is known as pearlash. The effect of the lime added to the