This mixture contains only about seven per cent of potash and would not prove profitable when used at a distance from the mines on account of the cost of freights. It has proved valuable, however, for a top dressing for meadow lands in the vicinity of Stassfurt.
244. Schönit.—Among the Stassfurt deposits there occurs in small quantities a mineral, schönit, which is composed of the sulfates of potassium and magnesium. The quantity of the mineral occurring naturally is very small and therefore it has no commercial importance. When, however, kainit is washed with water the common salt and magnesium chlorid which it contains being more soluble are the first leached out, and the residue has approximately the composition of the pure mineral. This mixture, as prepared in the way mentioned above, has the following average composition:
| Potassium sulfate | 50.40 | per cent. |
| Magnesium sulfate | 34.00 | “ |
| Sodium chlorid | 2.50 | “ |
| Water | 11.60 | “ |
The percentage of potash corresponding to the above composition is 27.2. This substance being so rich in potash, and practically free of chlorids, is well suited to transportation to great distances and for general use in the field. Since, however, a considerable expense attends the manufacture of the artificial schönit, the advantages above named give it very little, if any, advantage in competition with the other potash salts as they come from the mines. It has, however, an especial value for the fertilization of tobacco and vineyards.
245. Potassium Sulfate.—Several grades of potassium sulfate are found in the market for fertilizing purposes, some of them quite pure, containing over ninety-seven per cent of the pure sulfate. The following data show the composition of a high grade and low grade potassium sulfate of commerce:
| High grade. | Low grade. | |||
| Potassium sulfate | 97.20 | per cent. | 90.60 | per cent. |
| Potassium chlorid | 0.30 | “ | 1.60 | “ |
| Magnesium sulfate | 0.70 | “ | 2.70 | “ |
| Magnesium chlorid | 0.40 | “ | 1.00 | “ |
| Sodium chlorid | 0.20 | “ | 1.20 | “ |
| Insoluble | 0.20 | “ | 0.30 | “ |
| Water | 0.70 | “ | 2.20 | “ |
Naturally, high grade sulfates of this kind can only be prepared in chemical factories built especially for the work. The result is that the potash per unit is raised greatly in price. When, however, the fertilizers are to be transported to a great distance, the saving in freight often more than compensates for the higher price of the potash. It therefore happens that there are many places in this country where the actual price of potash per pound is less in high grade sulfates than in kainit or carnallit. When, in addition to this, the especial fitness of the high grade sulfates for certain forms of fertilization, especially tobacco growing, is considered, it is seen that at this distance from the mines these high grade salts are of no inconsiderable importance. The percentage of potash in the high grade sulfates often exceeds fifty.
246. Potassium Magnesium Carbonate.—This salt has lately been manufactured and used to a considerable extent, especially for tobacco fertilizing. As furnished to the trade it has the following average composition:
| Potassium carbonate | 35 to 40 | per cent. |
| Magnesium carbonate | 33 to 36 | “ |
| Water of crystallization | 25 | “ |
| Potassium chlorid, potassium sulfate, | ||
| and insoluble | 2 to 3 | “ |
The content of potash, as is seen from the above formula, amounts to from seventeen to eighteen per cent. The compound is completely dry, is not hygroscopic, and is, therefore, always ready for distribution. It is especially to be recommended for all those intensive cultures where it is feared that chlorids and sulfates will prove injurious, especially in the cultivation of tobacco.