=255. Methods Used at the Halle Station.=—(1) _In Kainits and other Mineral Salts of Potash._[204]—Five grams of the prepared sample are boiled for half an hour in a half liter flask with from twenty to thirty cubic centimeters of concentrated hydrochloric acid and 100 cubic centimeters of water, and afterwards as much water added as is necessary to fill the flask about three quarters full, and the sulfuric acid is then precipitated with barium chlorid. To avoid an excess of barium chlorid the solution used is of known strength and is added first in such quantity as would precipitate the sulfuric acid from a kainit of low sulfuric acid content. The mixture is then boiled, allowed to settle and tried with a dropping tube containing barium chlorid. If a further precipitate be given a few drops more of barium chlorid solution are added, again boiled and allowed to settle. This is continued until barium chlorid gives no precipitation. After the barium chlorid gives no more precipitate a drop of dilute sulfuric acid is added to test for excess of barium. The operation is continued with the sulfuric acid until it no longer gives a precipitate of barium sulfate. By the alternate use of the barium chlorid and sulfuric acid the exact neutral point can soon be secured. When this point is reached the liquid is allowed to cool, the flask is filled to the mark, its contents filtered, and of the filtrate fifty cubic centimeters, equal to half a gram of the substance, taken for further estimation. This quantity is evaporated on a water-bath to a sirupy consistence in a porcelain dish with ten cubic centimeters of platinic chlorid. The platinic chlorid solution should contain one gram of platinum in each ten cubic centimeters. The residue is treated with eighty per cent alcohol and, with stirring, allowed to stand for an hour. The precipitate is then collected on a gooch, either of platinum or porcelain, washed about eight times with eighty per cent alcohol and the potassium platinochlorid dried for two hours at 100°. After weighing the precipitate is dissolved in hot water and the residue washed under pressure, first with hot water and then with alcohol. The crucible with the asbestos felt is dried at 100° and weighed. Any impurities which the double salt may have carried down with it are left on the filter and the weight of the original precipitate can thus be corrected. The weight of potassium platinochlorid is multiplied by 0.1927 and the product corresponds to the weight of K₂O in the sample taken.