Silver Platinum. Bodies neither fused nor reduced. The alkaline earths, the earths, oxides of cerium, oxide of uranium, columbic acid. V. Blowpipe action with borax—colour of beads. — Experiments with borax or carbonate of soda are generally conducted on platinum wire. VI. Blowpipe action with salt of phosphorus. Gray Gray Green Brown Colourless Green } Green Gray. colour of beads.— Microcosmic salt, or ammonia-phosphate of soda, when heated, parts with its ammonia, and is converted into biphosphate of soda. The alkaline earths, earths and other bodies not enumerated, give colourless or milky beads in both flames. TESTING TABLES. Mode of using the Tables. To discover the nature of the acid, a solution of the substance to be tested is dissolved in a small portion of distilled water. A portion of the solution is poured into a test-glass, three drops of nitrate of silver are added, and the first column examined to observe if the precipitate corresponds with any of those described. Another portion is placed in a second test-glass, and three drops of a solution of chloride of barium added. If the acid be a common one, it will be found in the table. If it is of rarer occurrence we must look for it in the body of the work. For the bases we proceed in a similar manner. The reagents required in these experiments are described in the body of the work. The principal are hydrochloric acid, sulphuric acid, nitric acid, acetic acid, caustic ammonia, caustic soda and potash, chloride of barium, nitrate of barytes, oxalate of ammonia, sulphohydric acid, sulphohydret of ammonia, bichloride of platinum, nitrate of silver, phosphate of soda, solution of sulphate of lime. Testing Analyses. By means of the tables we should not only be able to distinguish the presence of single bases when present, but also to discriminate between a series of bases, supposing them to be mingled together. The following examples point out the method of working the tables : : -- PROCESSES FOR TESTING. 19% EXAMPLE OF TWO ACIDS IN SOLUTION. Add to a portion of the solution 3 drops of nitrate of silver : a white, curdy precipitate falls, which does not disappear when NO, is added, even after boiling. It dissolves in NH. It is, therefore, chlorohydric acid, the precipitate formed being chloride of silver. Add to a second portion 3 drops of solution of BaCl; a white powder falls, insoluble in NO,, which is BaO SO, indicating the presence of SO, in the solution. The solution then contains the two acids, HCl and SO3. EXAMPLE OF TWO BASES IN SOLUTION. Add 2 drops of NH, slowly a brownish precipitate falls, with a white shade. The addition of a few drops more of the NH, removes the white tint; a reddish brown precipitate remains undissolved. Throw the whole on a filter. To the filtered liquid add HCl till the solution renders litmus paper slightly red. When a drop of NaO is added to a portion of it, a white, flocky precipitate appears. An excess of soda redissolves the precipitate. SH, when passed through another portion, gives a white precipitate; and NH,SH has a similar effect, not redissolved in excess. The precipitate dissolved by NH, is, therefore, oxide of zinc. The reddish brown precipitate on the filter is dissolved off by dilute HCI. On the addition of NaO to a portion of the solution, a reddish brown precipitate falls. SH drops sulphur when passed through another portion of the solution. NH, SH renders another portion black; while yellow prussiate of potash yields with another portion Prussian blue. The precipitate undissolved by the NH, is therefore sesquioxide of iron. PROCESS WHEN THE PRECIPITATE IS WHITE. Supposing the precipitate to be of an unmixed white colour, we observe from the first table that it may be one or more of twelve bodies, and besides, when we have added an excess of NH,, that there may be a base held in solution by that reagent. The first step then is to filter the liquid; the precipitate remains on the filter, and the ammoniacal liquor passes through. We saturate the latter with a few drops of acid, and then add ammonia drop by drop, and watch carefully if any precipitation takes place before an excess is added. If a precipitate appears and is again dissolved, the substance belongs to Class III. If no precipitate appears, some of the substances included under Class II. may be present, which are therefore to be tested for by the appropriate reagents. Dilute hydrochloric acid is now to be poured on the filter, when the precipitate will pass through in solution. Caustic soda is to be added in excess to the solution of the precipitates, and the liquid filtered. The filtered liquor is to be saturated with HCl, and NH, added. If a precipitate appears, it must be one or more of the following substances: as these are the only white hydrous oxides which are soluble in caustic alkalies. To distinguish these, we find by Table III. that lead and tin are precipitated by SH, while alumina and glucina are not affected. We, therefore, dissolve the precipitate in HCl, and pass a current of SH through the solution. If a black precipitate appears, it may consist of both lead and tin. The precipitate is thrown on a filter, and washed with sulphohydret of ammonia. If tin is present it will be dissolved, and pass through the filter, while the lead will remain as a black precipitate. To detect the tin the filtered liquor is boiled with HCl till SH is driven off, and the distinguishing tests for tin employed. The sulphuret of lead on the filter is dissolved in HCl, and tested with SO, and chromate of potash. If alumina and glucina are present, they will remain dissolved in the liquid through which the SH has been passed. The gas is to be boiled away, and carbonate of ammonia added in excess. If alumina is present it will remain undissolved, while the glucina will be dissolved by the alkali. The liquid is therefore to be filtered, the solution which passes through neutralised by HCl, and NH, added. If glucina is present it will fall. The substances which may remain on the filter which are insoluble in caustic soda are the following Magnesia Cerium oxides Zirconia Titaniate The first 6 are not precipitated by SH, while the three last are precipitated by SH, as appears by Table III. By transmitting a stream of SH through the solution, therefore, these three metals will be precipitated. After filtration, by adding NH3SH, according to Table IV., the antimony will be dissolved, and may be precipitated from its solution by boiling the liquor and passing SH through it. An orange precipitate will fall. The bismuth and mercury may be separated by evaporating to dryness, dissolving the residue in NO, and adding water, the trisnitrate will precipitate as a white powder, while after filtration the mercury may be precipitated as yellow hydrate with caustic soda. or as iodide, by means of iodide of potassium, in the form of a beautiful red powder. The precipitate on the filter is dissolved in HCl, the solution neutralised, and NH,SH added. Magnesia, if present, will remain in solution, while the titanic acid and earths will be thrown down in the form of bulky white precipitates. After filtration the magnesia may be precipitated by phosphate of soda and carbonate of NH,. The earths remaining on the filter are now to be distinguished. The oxides of cerium and lantanum, and zirconium and yttrium, are first separated by means of a saturated solution of sulphate of potash; a double salt is formed insoluble in the solution. The double salt of zirconia is nearly insoluble in water and acids, while those of the other two earths can be dissolved in much water. Zirconia, after ignition, is insoluble in acids, SO, excepted, while yttria is soluble in the same circumstances. Titanic acid is easily distinguished by its being precipitated by boiling, and when precipitated, by its insolubility in HCl. 3 PROCEEDING WHEN THE PRECIPITATE IS COLOured. By acting on the precipitate with caustic soda we separate oxide of chrome and oxide of iridium, which are both soluble in that reagent. These may be separated from each other by NH,SH, which throws down iridium, and redissolves it, but not chrome. The remaining oxides may then be divided into those which are precipitated by SH, and those which are not acted on by that gas. The precipitate is to be washed by decantation, and then treated with an excess of NH,SH. The following will be dissolved: These are then to be tested for by the distinguishing tests. |