This salt contains its potash both as chloride and as sulphate. It also contains sodium and magnesium chlorides. It contains about 16 per cent potash. Owing to the pres ence of chlorides it has the same effect as kainite.
Muriate (Chloride) of This is a more concentrated form of potash than either of those just mentioned. It contains about 50 per cent of potash, making it 80 per cent potas sium chloride. The impurities are largely so dium chloride and insoluble mineral matter. A purer form of muriate of potash may be ob tained which contains 98 per cent pure potas sium chloride.
Sulphate of High-grade sulphate of potash contains from 49 to 51 per cent of potash. Its advantage over muriate is that it is not, like the latter, injurious to any crops; but it has the disadvantage of being more ex pensive.
This is a double sulphate of potash and magnesium. It contains about 26 per cent of potash. The cost of the potash is greater than in the muriate. The sulphate of magnesium it contains is supposed to have a beneficial effect upon the soil.
Potash Production in the United States.— The potash resources of the United States are most inadequate to meet the present needs owing to the loss of the German supply from the autumn of 1914 to the present (1918). In 1911 this country imported, mainly from Ger many, 672,639,518 pounds of potash salts valued at $11,826,106. There have recently been many efforts made to obtain potash in a form suit able for use as a fertilizer. Wood ashes con stituted about the only domestic source of pot ash supply previous to 1914. At present the largest quantity comes from some of the alkali lakes of the arid or semi-arid regions, the waters of which carry enough potash in solution to make its recovery profitable at present prices.
Another source of potash is the kelp or giant sea weed that grows in the Pacific Ocean from Lower California to Alaska. The ash of the plants contain about 30 per cent of potash. Machinery has been built for harvesting the plants and the operation of recovering potash has been conducted on a small scale. It is not likely, however, that the quantity of potash secured in this way will ever constitute any large part of the total amount required by the fertilizer industry of this country.
Alunite, a hydrous sulphate of potash and alumina, is a possible source of potash and one that has been worked in a small way. Several
processes for the extraction of potash from this mineral have been proposed and the recovery of potassium sulphate appears to be a rather simple matter.
Another enterprise that has been tried with some degree of success is the recovery of potash from the 'flue 'dust of Portland cement plants, some potash bearing rocks or minerals being added to the raw products used in the burning process.
The extraction of potash from silicate rocks has received a great deal of attention during the last few years. Among the materials used experimentally for this purpose are feldspar, of which there are small deposits scattered widely over the United States; leucite, occurring as one constituent of a rock of which immense quan tities are found in Wyoming; sericite, in ex tensive beds in Georgia, and green sand, of which large deposits are found in New Jersey.
By application of heat and fluxes to lower the melting point of the slag, it has been found possible to convert almost all of the potash into a form soluble in 2 per cent citric acid or into a condition considered to be available to plants. One distinct disadvantage which these silicates possess is that their content of potash is low and much material must be handled in order to obtain the rather small percentage of potash.
By means of these various processes there were produced in the United States during 1916 a total quantity of 20,000,000 pounds of potash salts, valued at $3,500,000.
Other Fertilizing are a number of fertilizers not included in the classes already mentioned. Many of them are very valuable sources of fertility.
Wood For some time after the use of fertilizers became an important farm prac tice, wood ashes constituted a large portion of the supply of potash. They also contain a con siderable quantity of lime and a small amount of phosphoric acid. The product known as un leached wood ashes contains 5 to 6 per cent of potash, 2 per cent of phosphoric acid and 30 per cent of lime. Leached wood ashes contain about 1 per cent of potash, 1.5 per cent of phosphoric acid and 28 to 29 per cent of lime. They con tain the potash in a readily available form as potassium carbonate. The lime conduces to a good physical condition of the soil.