(1) Preparation of the Sample.—It is advisable to take from a large well mixed mass at least half a kilogram for the analytical sample and this should be ground to a fine powder in a mill or mortar.
(2) Estimation of the Potash by the Precipitation Method.—In a half liter flask are placed 35.70 grams of kainit or sylvinit, or 30.56 grams of carnallit or bergkieserit, which are boiled with 350 cubic centimeters of water after the addition of ten cubic centimeters of hydrochloric acid. After cooling the flask is filled to the mark with water, well shaken, and its contents filtered. Fifty cubic centimeters of the filtrate are treated in a 200 cubic centimeter flask with a solution of barium chlorid, the flask filled to the mark, well shaken, and its contents filtered. Twenty cubic centimeters of the filtrate, corresponding to 0.3570 or 0.3056 gram of the substance, are treated with five cubic centimeters of platinic chlorid solution and the potassium estimated according to the usual methods.
(3) Estimation of Potash (K₂O) in Raw Potash Salts.—(a) For the determination of potash alone in carnallit, kainit, and sylvinit one hundred grams of the well-mixed sample are put into a graduated flask holding one liter and dissolved by boiling with half a liter of water, acidulated with ten cubic centimeters of hydrochloric. The purpose of adding hydrochloric acid is to bring any polyhalit that might be present in the salts into solution and which it is difficult to dissolve in pure water. After dissolving and cooling the flask is filled up to the mark. The solution, after mixing, is filtered through a dry filter and 100 cubic centimeters of the filtrate, corresponding to ten grams substance, are put into a half liter flask by means of a pipette. After the addition of 200-300 cubic centimeters of water the solution is heated to boiling and the sulfuric acid accurately precipitated with normal barium chlorid solution, containing 104 grams of the dry salt in one liter. The volume of the precipitate is calculated from the amount of barium solution used and from the specific gravity of the barium sulfate. After cooling, the flask is filled up with water as far above the mark as equals the volume of the calculated barium precipitate, and, after thorough mixing, the solution is filtered again through a dry filter. Fifty cubic centimeters of this filtrate, corresponding to one gram substance, are evaporated upon the water-bath with a sufficient amount of platinic chlorid. The residue of potassium platinochlorid is washed with ninety per cent alcohol, dried at 120°, and weighed.
(b) If it be desired to determine separately the quantity of potash present in the form of sulfate and in the form of chlorid, as for example in kainit and in sulfate of potash, or if it is to be determined whether potassium sulfate is in combination with a proportionate amount of magnesium chlorid, as in kainit, or in combination with magnesium sulfate alone, as in schönit, it then becomes necessary to determine besides potash the percentages of chlorin, sulfuric acid, lime, magnesia, the total alkalies, water, and the residue insoluble in water. For this purpose 100 grams of the sample are dissolved, the solution is filtered, the filter washed, and the filtrate made up to one liter; a part of the liquid is taken for the determination of sulfuric acid; by precipitating with barium chlorid, and another part for the determination of lime and magnesia. For the determination of the alkali chlorids, 100 cubic centimeters of the solution, corresponding to ten grams substance, are acidulated with hydrochloric, and, after heating to boiling, the sulfuric acid is completely precipitated with barium chlorid, with the precaution of using not more of the barium solution than is necessary for the complete precipitation. Fifty cubic centimeters of the filtered solution, corresponding to one gram substance, are evaporated to dryness in order to drive off the hydrochloric acid. Magnesium chlorid is decomposed by igniting with oxalic acid or with mercuric oxid. After ignition, the residue is moistened with a little ammonium carbonate for the purpose of converting the calcium oxid that may have been formed into calcium carbonate. The alkali chlorids, which are entirely free of lime and magnesia, are weighed, and potassium chlorid is determined by means of platinic chlorid. The amount of sodium chlorid is obtained by deducting potassium chlorid from the mixed chlorids. For the water determination five grams of the sample are ignited and the loss of weight is determined. The ignited mass is dissolved in water, and for the purpose of determining the quantity of magnesium chlorid that may have been decomposed by the ignition the percentage of chlorin is determined by titration. The difference in the contents of chlorin before and after ignition is subtracted from the loss in weight, after allowance has been made for the absorption of oxygen and for the loss of hydrogen. The rest is water. The results obtained are calculated in the following manner: From the total amount of the sulfuric acid found, that portion is deducted which is combined with calcium as calcium sulfate; the rest of the sulfuric acid is divided into two equal parts for the purpose of calculating the contents of potassium sulfate and magnesium sulfate, according to the molecular proportion in which these salts are present in kainit and in schönit. If there be an excess of potash left uncombined with sulfuric acid, then it is in the form of potassium chlorid; likewise the amount of magnesia, uncombined with sulfuric acid, is to be reckoned as magnesium chlorid. The result of this calculation will tell how much potash is in the form of kainit (K₂SO₄, MgSO₄, MgCl₂ with 6H₂O) and how much of it is in the form of schönit (K₂SO₄, MgSO₄, with 6H₂O) and how much in the form of potassium chlorid. The sodium is reckoned as sodium chlorid.
(c) In calculating the contents of potash, of potassium chlorid, and of potassium sulfate from the weighed potassium platinochlorid, the factors 0.1928, 0.3056, and 0.3566 are used, assuming that the atomic weight of platinum is 197.18.
(d) The two methods which have been described under a and b, and which are in common use in the Stassfurt potash industry, i. e., the so-called precipitation method, and the oxalic acid method, give almost identical results. The first method, however, deserves preference on account of greater simplicity in cases where potash alone is to be determined. Finkner’s method likewise gives results which agree well with the results obtained by the customary methods. It consists in evaporating the salt solution with a sufficient quantity of platinic chlorid without previously removing the sulfuric acid, reducing the potassium platinochlorid, and weighing the metallic platinum.
The following are the results of comparative analyses:
| 1. After the precipitation method | 22.02 per cent KCl |
| 2. After the oxalic acid method | 22.03 per cent KCl |
| 3. After Finkner’s method | 22.01 per cent KCl |
In another sample of carnallit the following results were obtained:
| 1. After the precipitation method | 17.88 per cent KCl |
| 2. After the oxalic acid method | 17.88 per cent KCl |