ALKALIES AND ALKALINE EARTHS.
The separation of these bodies in the caustic state is a matter of difficulty owing to the great tendency they possess to become converted into carbonates; the carbonates of lime, baryta and strontia, moreover, being non-poisonous in their effects, will not be employed with criminal intent, and the carbonates of soda and potassa are extensively used as pharmaceutical preparations. Notwithstanding the small chances of success, the isolation of the compounds under consideration in the caustic state is to be attempted.
To this intent, the organs to be analysed, together with their contents, are placed in a glass retort provided with a receiver, water added, and the mixture boiled. The distillate will contain the ammonia present. When, however, putrefaction has begun, the detection of this compound does not necessarily indicate its original presence in the suspected materials. If, after an hour's boiling, the fluid in the retort possess an alkaline reaction, it is to be examined for soda, potassa, strontia, baryta and lime. The undistilled solution is filtered, the filtrate evaporated to dryness, and the residual mass treated with alcohol. By this treatment, potassa and soda go in solution, lime, baryta and strontia[I]—as well as the alkaline carbonates—remaining undissolved. The potassa and soda are separated from the other salts present by filtering and evaporating the alcoholic solution to dryness and then calcining the residue in a silver crucible. The mass, which should still be alkaline, is then dissolved in dilute sulphuric acid. If the solution is turbid, traces of baryta or strontia may still be present and should be removed by filtration. Some hydrochloric acid and solution of bichloride of platinum are then added to a portion of the filtered liquid: in presence of potassa a yellow precipitate is formed.
Another portion is treated with tartaric acid: a white granular precipitate is produced. Hydrofluosilicic acid is added to a third portion of the solution: the formation of a gelatinous precipitate is a further indication of the presence of potassa. If the preceding tests have given negative results, and a white precipitate is formed by the addition of antimonate of potassa to another portion of the solution, soda is present. In both cases, it is necessary to confirm the results by means of the spectroscope.
The above reactions are distinctive only in the absence of metals precipitated by sulphuretted hydrogen, sulphide of ammonium or carbonate of soda, and small portions of the solution should be tested with these reagents.
In order to detect baryta, strontia and lime, the residue, insoluble in alcohol is dissolved in dilute nitric acid, and an excess of carbonate of ammonia added to the solution: the three bases, if present, are precipitated as carbonates. The precipitate formed is separated from the solution by filtration, dissolved on the filter in dilute hydrochloric acid, and the solution then filtered and divided into two parts: sulphuric acid is added to one, the fluid filtered from the precipitate of sulphate of baryta formed, and the filtrate treated with ammonia and oxalate of ammonia. If lime be present,—although its sulphate is not easily soluble—sufficient will be contained in the filtrate to give a white precipitate of oxalate of lime.
The remaining portion of the solution is evaporated to dryness, and the residue treated with absolute alcohol. Chloride of strontium goes into solution, chloride of barium remaining undissolved. If upon evaporating the alcoholic solution a residue is obtained which, when dissolved in water, produces turbidity in a solution of sulphate of lime, strontia is present.
The residue, insoluble in alcohol, is dissolved in water. If a precipitate is produced by the addition of sulphuric acid or hydrofluosilicic acid to the solution, baryta is present. The latter reaction distinguishes baryta from strontia, which is not precipitated by hydrofluosilicic acid. Should the tests mentioned above fail to give affirmative results, and poisoning by means of baryta and strontia be nevertheless suspected, these compounds may possibly have remained in the materials contained in the alimentary canal, in the state of insoluble sulphates. To effect their detection under these circumstances the organic substances must be decomposed by means of sulphuric acid. The carbonaceous residue is calcined in a crucible at an elevated temperature, and the remaining mass treated with water. In this way, a solution of sulphides of barium and strontium is obtained, which is then tested as directed above.