(2.) =Silico-Tungstic Acid as a Reagent for Alkaloids.=--Sodium tungstate is boiled with freshly precipitated gelatinous silica. To the solution is added mercurous nitrate, which precipitates the yellow mercurous silico-tungstate. This is filtered, well-washed, and decomposed by an equivalent quantity of hydrochloric acid; silico-tungstic acid then goes into solution, and mercurous chloride (calomel) remains behind. The clear filtrate is evaporated to drive off the excess of hydrochloric acid, and furnishes, on spontaneous evaporation, large, shining, colourless octahedra of silico-tungstic acid, which effloresce in the air, melt at 36°, and are easily soluble in water or alcohol. This agent produces no insoluble precipitate with any metallic salt. Cæsium and rubidium salts, even in dilute solutions, are precipitated by it; neutral solutions of ammonium chloride give with it a white precipitate, soluble with difficulty in large quantities of water. It precipitates solutions of the salts of quinine, cinchonine, morphine, atropine, &c.; if in extremely dilute solution, an opalescence only is produced: for instance, it has been observed that cinchonine hydrochlorate in 1/200000, quinia hydrochlorate in 1/20000, morphia hydrochlorate in 1/15285 dilution, all gave a distinct opalescence.--_Archiv der Pharm._, Nov., Dr. Richard Godeffroy. (3.) =Scheibler’s Method for Alkaloids: Phospho-Tungstic Acid.=--Ordinary commercial sodium tungstate is digested with half its weight of phosphoric acid, specific gravity 1·13, and the whole allowed to stand for some days, when the acid separates in crystals. A solution of these crystals will give a distinct precipitate with the most minute quantities of alkaloids, 1/200000 of strychnine, and 1/100000 of quinine. The alkaloid is liberated by digestion with barium hydrate (or calcium hydrate); and if volatile, may be distilled off, if fixed, dissolved out by chloroform. In complex mixtures, colouring-matter may be removed by plumbic acetate, the lead thrown out by SH₂, and concentrated, so as to remove the excess of SH₂. § 304. =Schulze’s reagent= is phospho-antimonic acid. It is prepared by dropping a strong solution of antimony trichloride into a saturated solution of sodic phosphate. The precipitation of the alkaloids is effected by this reagent in a sulphuric acid solution. § 305. =Dragendorff’s reagent= is a solution of potass-bismuth iodide; it is prepared by dissolving bismuth iodide in a hot solution of potassium iodide, and then diluting with an equal volume of iodide of potassium solution. On the addition of an acid solution of an alkaloid, a kermes-red precipitate falls down, which is in many cases crystalline. =Marm’s reagent= is a solution of potass-cadmium iodide. It is made on similar principles. =Potass-zinc iodide= in solution is also made similarly. The precipitates produced in solutions of narceine and codeine are crystalline and very characteristic.