Estimation of Potassium Chlorid and Potassium Sulfate in Calcined Manurial Salts.—In these salts 15.281 grams for potassium chlorid or 17.847 grams for potassium sulfate are dissolved in a half liter flask after the addition of ten cubic centimeters of hydrochloric acid. The flask is filled to the mark and its contents filtered and 250 cubic centimeters placed in a half liter flask and treated with barium chlorid solution as indicated above. The rest of the operation is exactly as has been described. In each case one milligram of the potassium platinochlorid corresponds to one-tenth per cent of the desired salt.
Estimation of Magnesium Sulfate in Kieserit.—Ten grams of the finely powdered kieserit are boiled for one hour in a half liter flask two-thirds full of water. After cooling, from fifty to sixty cubic centimeters of double normal potash lye and twenty cubic centimeters of a ten per cent neutral potassium oxalate solution are added, the flask filled to the mark, and after being well shaken and standing for a quarter of an hour, filtered. The reaction is represented by the formula
MgSO₄ + 2KOH = MgO₂H₂ + K₂SO₄.
Fifty cubic centimeters of the filtrate are then titrated with one-tenth normal sulfuric acid. To the percentage of magnesium sulfate found by this process two-tenths per cent are to be added as a correction.
Barium Chlorid Solution.—Dissolve 122 grams of crystallized barium chlorid in water in a liter flask. Add fifty cubic centimeters of hydrochloric acid and water to the mark and shake well.
260. The Barium Oxalate Method.—The principle of this process, worked out by Schweitzer and Lungwitz[208] is based on the fact that in an ammoniacal solution, by means of barium oxalate, all the alkaline earths can be precipitated as oxalates, and sulfuric acid in similar circumstances can be thrown down as a barium salt and the iron and alumina as hydroxids. The reagents used to secure this precipitation are ammonia and barium oxalate.
For the determination of potash in a superphosphate the analytical process is conducted as follows: Ten grams of the superphosphate are mixed with half a liter of water and fifteen grams of barium oxalate dissolved in hydrochloric acid.
The mixture is boiled for twenty minutes and treated with some hydrogen peroxid to oxidize any ferrous iron that may be present. Afterwards the solution is made alkaline with ammonia. After cooling, it is made up to a given volume (half a liter) and filtered. An aliquot part of the filtrate is evaporated to dryness, ignited, extracted with hot water and, after the addition of a few drops of hydrochloric acid, the potassium is precipitated with platinic chlorid, and collected and weighed in the usual manner: Or the ignited residue may be dissolved directly in dilute hydrochloric acid and the rest of the process carried out as indicated.
In kainit the process is conducted as follows: Ten grams of the powdered sample are treated with a hydrochloric acid solution of the barium oxalate containing ten grams of the salt. The rest of the operation is conducted as described above. In the use of this method it is important that always enough of the barium oxalate solution be employed to fully saturate all the sulfuric acid which may be present.
261. Method of DeRoode for Kainit.—All the potash contained in kainit, according to de Roode, passes readily into aqueous solution.[209] On evaporating this aqueous solution to a pasty condition with enough platinic chlorid to unite with all the halogens present all the other bodies can be washed out of the potassium platinochlorid by ammonium chlorid solution and the pure platinum salt thus obtained, which is washed and dried in the usual way. De Roode therefore asserts that it is quite useless to previously precipitate the solution of kainit with barium chlorid, ammonium oxalate, or carbonate. Before the addition of alcohol to the residue obtained by evaporation with platinic chlorid the sodium sulfate present renders the platinum salt sticky and difficult to wash, but the disturbing sodium compound can be readily removed by washing with ammonium chlorid solution.