252. Alternate Method for Potash.—Boil ten grams of the prepared sample for thirty minutes with 300 cubic centimeters of water, and, after cooling and without filtering, make up to one liter and filter through a dry filter. If the sample have ten per cent of potassium oxid, use fifty cubic centimeters of the filtrate; if less than ten per cent of potassium oxid (ordinary potash fertilizers), use 100 cubic centimeters of the filtrate. In each case make the volume up to 150 cubic centimeters, heat to 100°, and add, drop by drop with constant stirring, a slight excess of barium chlorid, and, without filtering, in the same manner add barium hydrate in slight excess. Filter while hot and wash until the precipitate is free of chlorids. Add to the filtrate one cubic centimeter of strong ammonium hydrate, and then a saturated solution of ammonium carbonate, until the excess of barium is precipitated. Heat and add, in fine powder, a half gram of pure oxalic acid or 0.75 gram of ammonium oxalate. Filter, wash free of chlorids, evaporate the filtrate to dryness in a platinum dish, and ignite carefully over the free flame, below red heat, until all volatile matter is driven off.
The residue is digested with hot water, filtered through a small filter, and washed with successive small portions of water until the filtrate amounts to thirty cubic centimeters or more. To this filtrate, add two drops of hydrochloric acid, in a porcelain dish, and from five to ten cubic centimeters of a solution of ten grams of platinic chlorid in 100 cubic centimeters of water. The mixture is evaporated on a water-bath to a thick sirup, as above, treated with alcohol of eighty per cent strength, washed by decantation, collected in a gooch or other form of filter, washed with strong alcohol, afterwards with five cubic centimeters of ether, dried for thirty minutes at 100°, and weighed.
It is desirable, if there be an appearance of foreign matter in the double salt, that it should be washed, according to the previous method, with ten cubic centimeters of the half-concentrated solution of ammonium chlorid, which has been saturated by shaking with potassium platinochlorid.
253. Method of Solution for Organic Compounds.—In case the potash is contained in organic compounds, like tobacco stems, cottonseed hulls, etc., weigh ten grams, saturate with strong sulfuric acid, and ignite in a muffle to destroy organic matter. Add a little strong hydrochloric acid to moisten the mass and warm slightly so as to loosen it in the dish. Proceed then as in the lindo-gladding or alternate method.
254. Factors.—The use of the factors 0.3056 for converting potassium platinochlorid to potassium chlorid and 0.19308 for converting it to potassium oxid is advised. The latter number is almost identical with that used by the Halle and Stassfurt chemists viz., 0.1927 and 0.1928 respectively.
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.
(2) Estimation of Potash in Guanos and Other Fertilizers containing Organic Substances.—Ten grams of the substances are carefully incinerated at a low temperature in a platinum dish. After ignition the contents of the dish are placed in a half liter flask and boiled for an hour with hydrochloric acid and a few drops of nitric acid. The sulfuric acid can then be precipitated directly with barium chlorid, or better, allow the flask to cool, fill to the mark, filter and treat an aliquot part of the filtrate with barium chlorid as described above. The filtrate from the separated sulfate of barium is neutralized with ammonia and all the bases, with the exception of magnesia and the alkalies, precipitated with ammonium carbonate; boil, fill to the mark and filter. Of this filtrate evaporate from 100 to 200 cubic centimeters in a platinum dish. After evaporation the ammonium salts are driven off by careful ignition, the residue taken up with hot water and filtered through as small a filter as possible into a porcelain dish; the magnesia remaining in the precipitate. The filtrate is acidified with a few drops of hydrochloric acid, ten cubic centimeters of platinic chlorid added and the further determination conducted as with kainit.
256. Dutch Method.—The process used at the Royal Agricultural Station of Holland is almost identical with that employed at Halle.[205]
A. Method for Stassfurt and other Potash Salts.—The necessary reagents are: