In a third sample of carnallit the content of potassium chlorid was as follows:
| 1. After the precipitation method | 18.44 per cent KCl |
| 2. After the oxalic acid method | 18.38 per cent KCl |
The Anhalt chemists object to precipitating the sulfuric acid and alkaline earths with barium oxid and ammonium carbonate, and afterwards the potash with platinic chlorid. The results obtained with this method are, according to them, very inaccurate, and always too low. This is explained by the fact that it is impossible to precipitate sulfuric acid without at the same time precipitating some of the potash, unless it be in an acid solution.
A separation of the alkaline earths, if potash alone is to be determined, is superfluous, for the reason that calcium and magnesium platinochlorid are soluble in ninety per cent alcohol, even with more facility than sodium platinochlorid.
259. Methods for Concentrated Potash Salts.—In the preceding paragraphs have been given the methods used by the Stassfurt syndicate for the estimation of potash in the raw salts as they come from the mines. Following are the methods used by the same syndicate for the concentrated approximately pure compounds and the other salts which accompany them.
Potassium Chlorid.—The following process is used for the estimation of potassium and other constituents of the high grade chlorids of commerce. In a half liter flask are placed 7.6405 grams of the finely powdered sample, which is dissolved and made up to the mark. With salts which contain more than half a per cent of sulfuric acid the preliminary conversion of the sulfates into the corresponding chlorin compounds, by precipitation with barium chlorid solution, is necessary. Twenty cubic centimeters of the above solution, corresponding to 0.3056 gram of the salt, are placed in a flat porcelain dish having a diameter of about ten centimeters and, after the addition of five cubic centimeters of the platinic chlorid solution, evaporated on the water-bath with constant stirring until, after cooling, the sirupy liquid passes quickly into a fine crystalline condition. The residue is rubbed into a fine powder with a glass rod, mixed with twenty cubic centimeters of ninety-six per cent alcohol and dried at 120° to a constant weight. It is weighed while warm and brought on a moistened filter with alcohol, care being taken that the liquid does not touch the edge of the filter. The filtration can be carried on under a moderate pressure. The complete washing of the potassium platinochlorid can be easily accomplished upon the filter. The filter and the precipitate, after as much of the alcohol wash has been removed as is possible, are dried at 120° to constant weight and weighed while still warm. One milligram of the potassium platinochlorid thus obtained corresponds to a tenth per cent of potassium chlorid.
Estimation of Sodium Chlorid.—For the estimation of the sodium chlorid which may be present in the potassium chlorid twelve and a half grams of the latter salt are dissolved in a quarter liter flask with twenty-five cubic centimeters of boiling water after the addition of a little potassium carbonate for the purpose of converting the magnesium and calcium compounds into carbonates. After filtration 100 cubic centimeters corresponding to five grams of the salt are evaporated to dryness in a porcelain or platinum dish after the addition of a few drops of concentrated hydrochloric acid in order to convert any calcium carbonate which may be present into chlorid. The residue is gently ignited and weighed. In this mixture of potassium and sodium chlorids the potassium chlorid may be estimated in the usual way and the sodium chlorid determined by difference or the respective proportions of the two bases may be calculated after the determination of the total chlorin by precipitation with a standard solution of silver nitrate.
Estimation of Magnesium Chlorid.—In order to estimate the amount of magnesium chlorid in high grade muriate of potash, twenty-five grams of the latter salt are dissolved in a half liter flask and treated with ten cubic centimeters of a normal solution of potash lye. The flask is then filled to the mark with water, thoroughly shaken and its contents filtered. Fifty cubic centimeters of the filtrate are then titrated with one-tenth normal sulfuric acid. The calcium compounds which remain in solution do not influence the result. The quantity of magnesium chlorid originally present corresponds to the number of cubic centimeters of the normal potash lye which has disappeared in the operation. The reaction which takes place is represented by the following equation:
MgCl₂ + 2KOH = MgO₂H₂ + 2KCl.
Potassium Sulfate.—The quantity of potassium sulfate contained in the high grade sulfates of commerce is determined in the following manner: In a half liter flask are placed 8.9235 grams of the finely ground sample which is dissolved in about 350 cubic centimeters of boiling water after the addition of twenty cubic centimeters of hydrochloric acid. The sulfuric acid is thrown out by the addition, drop by drop, of a barium chlorid solution, the contents of the flask being kept boiling meanwhile and thoroughly stirred. From time to time the addition of the barium chlorid is stopped and the upper part of the liquid allowed to become clear by the subsidence of the barium sulfate. It is then noticed whether or not an additional drop of the barium chlorid solution produces a turbidity. Any excess of barium chlorid is removed by the careful addition of sulfuric acid. After the precipitation is complete and the contents of the flask are cooled, it is filled up to the mark with water and its contents filtered. Twenty cubic centimeters of the filtrate, corresponding to 0.357 gram of the original salt are precipitated by platinic chlorid in the usual manner and the resulting potassium platinochlorid collected and weighed. One milligram of the potassium platinochlorid thus obtained corresponds to one-tenth per cent of potassium sulfate in the original salt. To the percentage of potassium sulfate thus found three-tenths per cent are to be added for a correction when high grade potassium sulfate is taken. If the sample be a high grade sulfate of potassium and magnesium no correction should be applied.