is frequently necessary for the examination of blowpipe experiments, or the reaction of the fluxes. Common lenses, howsoever cheap they may be, are certainly not recommended. A microscope with achromatic lenses can now be purchased so cheap that there is no longer any necessity of procuring one with the common lens. Besides, there is no reliability whatever to be placed in the revelations of the common lens ; while on the contrary, the deceptive appearances which minute objects assume beneath such lenses are more injurious than otherwise. A small cheap set of magnifying glasses are all that is required for the purpose of blowpipe analysis, Fig. 12. Fig. 12. A small magnet should be kept on hand, for the purpose of testing reduced metals. Nippers, for the purpose of breaking off pieces of minerals for analysis, without injuring the entire piece, are indispensable, Fig 13. Fig. 13. A pair of scissors is required to trim the wick of the lamp, and for the trimming of the edge of platinum foil. A small spatula should be kept for the purpose of mixing substances with fluxes. THE REAGENTS. Those substances which possess the property of acting upon other substances, in such a characteristic manner that they can be recognized, either by their color, or by their effervescence, or by the peculiar precipitation produced, are termed reagents. The phenomena thus produced is termed reaction. We use those reagents, or tests, for the purpose of ascertaining the presence or the absence of certain substances, through the peculiar phenomena produced when brought in contact with them. The number of reagents employed in blowpipe analysis is not great, and therefore we shall here give a brief description of their preparation and use. It is indispensably necessary that they should be chemically pure, as every admixture of a foreign substance would only produce a false result. Some of them have a strong affinity for water, or are deliquescent, and consequently absorb it greedily from the air. These must be kept in glass bottles, with glass stoppers, fitted air-tight by grinding. A. REAGENTS OF GENERAL USE. 1. Carbonate of Soda.-(NaO, CO2) Wash the bicarbonate of soda (NaO, 2CO2) upon a filter, with cold water, until the filtrate ceases to give, after neutralization with diluted nitric acid (NO3), a precipitate with nitrate of baryta, (BaO, NO3), or nitrate of silver, (AgO, NO3). That left upon the filter we make red hot in a platinum, silver, or porcelain dish. One atom of carbonic acid is expelled, and the residue is carbonate of soda. A solution of soda must not be changed by the addition of sulphide of ammonium. And when neutralized with hydrochloric acid, and evaporated to dryness, and again dissolved in water, there must be no residue left. Carbonate of soda is an excellent agent in reduction, in consequence of its easy fusibility, whereby it causes the close contact of the oxides with the charcoal support, so that the blowpipe flame can reach every part of the substance under examination. For the decomposition and determination of insoluble substances, particularly the silicates, carbonate of soda is indispensable. But for the latter purpose, we use with advantage a mixture of ten parts of soda and thirteen parts of dry carbonate of potash, which mixture fuses more easily than the carbonate of soda alone. 2. Hydrate of Baryta (BaO, HO). This salt is used sometimes for the detection of alkalies in silicates. Mix one part of the substance with about four parts of the hydrate of baryta, and expose it to the blowpipe flame. The hydrate of baryta combines with the silicic acid, and forms the super-basic silicate of baryta, while the oxides become free. The fused mass must be dissolved in hydrochloric acid, which converts the oxides into chlorides. Evaporate to dryness, and dissolve the residue in water. The silicic acid remains insoluble. The hydrate of baryta is prepared by mixing six parts of finely powdered heavy-spar (BaO, SO3) with one part of charcoal and one and a half parts of wheat flour, and exposing this mixture in a Hessian crucible with a cover to a strong and continuous red heat. The cooled chocolate-brown mass must be boiled with twenty parts of water, and, while boiling, there must be added the oxide of copper in sufficient quantity, or until the liquid will not impart a black color to a solution of acetate of lead (PbO, Ã). The liquid must be filtered while hot, and as it cools the hydrate of baryta appears in crystals." These crystals must be washed with a little cold water, and then heated at a low temperature in a porcelain dish until the crystal water is expelled. The hydrate of baryta melts by a low red heat without losing its water of hydration. 3. Bisulphate of Potassa (KO, 2S0').-At a red heat the half of the sulphuric acid of this salt becomes free, and thus separates and expels volatile substances, by which we can recognize lithium, boracic acid, nitric acid, fluoric acid, bromine, iodine, chlorine; or it decomposes and reveals some other compounds, as, for instance, the salts of the titanic, tantalic and tungstic acids. The bisulphate of potash is also used for the purpose of converting a substance into sulphate, or to free it at once from certain constituents. These sulphates are dissolved in water, by which we are enabled to effect the separation of its various constituents. PREPARATION. Two parts of coarsely powdered sulphate of potash are placed in a porcelain crucible, and one part of pure sulphuric acid is poured over it. Expose this to heat over the spirit-lamp, until the whole becomes a clear liquid. The cooled mass must be of a pure white color, and may be got out of the crucible by inverting it. It must be kept in a fine powder. 4. Oxalate of Potassa (KO, Ō).-—Dissolve bioxalate of potash in water, and neutralize with carbonate of potash. Evaporate the solution at a low heat to dryness, stirring constantly towards the close of the operation. The dry residue is to be kept in the form of a powder. The oxalate of potash, at a low red heat, eliminates a considerable quantity of carbonic oxide, which, having a strong affinity for oxygen, with which it forms carbonic acid, it is therefore a powerful agent of reduction. It is in many cases preferable to carbonate of soda. 5. Cyanide of Potassium (Cy, K).-In the dry method of analysis, this salt is one of the most efficient agents for the reduction of metallic oxides. It separates not only the metals from their oxygen compounds, but likewise from their sulphur compounds, while it is converted through the action of the oxygen into carbonate of potash, or, in the latter case, combines with the sulphur and forms the sulphureted cyanide of potassium. This separation is facilitated by its easy fusibility. But in many cases it melts too freely, and therefore it is better to mix it, for blowpipe analysis, with an equal quantity of soda. This mixture has great powers of reduction, and it is easily ab sorbed by the charcoal, while the globules of reduced metal are visible in the greatest purity. PREPARATION.-Deprive the ferrocyanide of potassium (2KCy + FeCy) of its water by heating it over the spirit-lamp in a porcelain dish. Mix eight parts of this anhydrous salt with three parts of dry carbonate of potash, and fuse the mixture by a low red heat in a Hessian, or still better, in an iron crucible with a cover, until the mass flows quiet and clear, and a sample taken up with an iron spatula appears perfectly white. Pour the clear mass out into a china or porcelain dish or an iron plate, but with caution that the fine iron particles which have settled to the bottom, do not mix with it. The white fused mass must be powdered, and kept from the air. The cyanide of potassium thus prepared, contains some of the cyanate of potassa, but the admixture does not deteriorate it for blowpipe use. It must be perfectly white, free from iron, charcoal, and sulphide of potassium. The solution of it in water must give a white precipitate with a solution of lead, and when neutralized with hydrochloric acid, and evaporated to dryness, it must not give an insoluble residue by dissolving it again in water. 6. Nitrate of Potassa, Saltpetre (KO, NO').-Saturate boiling water with commercial saltpetre, filter while hot in a beaker glass, which is to be placed in cold water, and stir while the solution is cooling. The greater part of the saltpetre will crystallize in very fine crystals. Place these crystals upon a filter, and wash them with a little cold water, until a solution of nitrate of silver ceases to exhibit any reaction upon the filtrate. These crystals must be dried and powdered. Saltpetre, when heated with substances easy of oxidation, yields its oxygen quite readily, and is, therefore, a powerful means of oxidation. In blowpipe analysis, we use it particularly to convert sulphides (as those of arsenic, antimony, &c.) into oxides and acids. We furthermore use saltpetre for the purpose of producing a complete oxidation of small quantities of metallic oxides, which oxidize with difficulty in the oxidation |