18. TIN. Sn. Tin foil is generally used, cut into little slips, half an inch broad, and tightly rolled. Tin serves for the highest degree of reduction in glass fluxes, where small quantities of oxides of the metals are present, which are capable of being reduced to a lower state of oxide, in which state the results are more convincing. The operator brings the globule, heated in the reducing flame, in contact with the free end of a rolled rod of tin. By this means a small portion of melted tin is deposited upon the flux. The whole is then fused perfectly in the reducing flame. When the tin has been added to the bead, which contains the substance for examination, an operator must not direct the flame upon the glass for too long a time, partly because the tin would become in such a state as to prevent metallic oxides, which should only be reduced to the state of protoxide, from manifesting their presence by the peculiar color imparted to the bead, or pearl, and partly because so much tin would be dissolved, particularly if phosphates were present, that the globule, upon cooling, would be quite opaque, thus rendering the analysis of no value. 19. SILVER WIRE. A small silver wire is useful for ascertaining the presence of hepar-sulphide of antimony,—or soluble sulphides. Silver which is obtained from the reduction of hornsilver-chloride of silver,and beaten into wires, is also necessary in many quantitative gold examinations. It is useful, with sulphide of ammonium, for separating yttria and zirconia from iron. It also detects small quantities of arsenic in metallic combinations; and is employed in quantitative cupellations. SECTION II. QUALITATIVE ANALYSIS WITH THE BLOWPIPE. Ir is well known that the miner frequently encounters substances, which, from their exterior appearances, he may have considered to belong to some certain class of minerals, but which, by subsequent chemical analysis, are proved to be of an entirely different constitution. It happens that in the earthy gangues of the more frequently occurring ores, minerals of great scarcity and value exist, but in such a minutely disseminated state as to be scarcely discernible with the aid of the microscope. Again, it is very difficult for the smelter to know the nature of the ingredients given him to assay. The mixed mass is given him ready for furnacing, and, except it be from previous experience, he is quite unable to judge, by its appearance the degree of heat necessary for its fusion; and difficulties may again stand in his way, with respect to the further working of his furnace products, from the presence of substances which he either does not know to be contained therein at all, or which he may consider to exist only to a very small extent. A means is wanted by which the miner and smelter can obtain the necessary information with respect to the ingredients of minerals, ores, and furnace products, and as it seldom happens that there is a laboratory within such a distance as to be available upon every emergency, the Blowpipe affords the only resource from which this knowledge may be obtained with certainty. By means of the Blowpipe, the substances which comprise a mixed mass can in all cases be determined. It is, therefore, my intention now to treat of the Blowpipe as the agent for Qualitative Analysis. I will describe the qualitative examination of alkalies, earths, metals, their oxides, and the non-metallic bodies, so far as they have come under my own observation; and I shall attach to each the name, some instruction as to its nature, whence derived, and the mineralogical or chemical formula; and I will also give general rules, in as short and concise terms as possible, with respect to the comportment of earths, metallic oxides, et cetera, before the Blowpipe alone, or with borax, microcosmic salt, carbonate of soda, and a solution of nitrate of cobalt; and also a description of the different appearances presented by the sublimates of some metals, when heated upon charcoal. I.-GENERAL RULES FOR QUALITATIVE TA General Rules by which the ingredients of Minerals, et cetera, may, for the most part, be detected, when heated alone or with reagents in the Blowpipe flame. It is always advisable, before commencing an analysis, to spread a sheet of clean glazed paper upon the table, on the middle of which the Blowpipe lamp is placed; by this precaution, any substance falling from the charcoal or wire can be re-obtained, and the investigation continued. If it is of any consequence that the table be preserved from the hot falling assays, three or four sheets must be employed. The presence of foreign matter upon the paper must be particularly guarded against, otherwise, on a bead falling and coming in contact with it, a false result would necessarily follow. Fresh paper should be employed for each analysis. |