PRELIMINARY EXAMINATION OF INORGANIC SUBSTANCES. When a substance is submitted for qualitative analysis, the chemist first notes its color and form—the latter with the aid of a simple magnifying glass. The substance is then usually subjected to an examination by means of the blowpipe (q.v.) or the non-luminous gas flame. (See FLAME.) Blowpipe analysis has been elaborated into a systematic scheme for the de tection of all the important metallic and of some acidic radicals, and has proved of- great value, especially to the mineralogist. The chemist, as a rule, makes only a brief examination to deter mine the general nature of the substance, and to answer such questions as whether water, or ganic matter, silicates, complex cyanides, large quantities of an easily reducible metal, sulphur and arsenic, are or are not present, such con stituents often rendering necessary a modification of the usual scheme of systematic analysis. Beating a small portion of the substance in a closed glass tube reveals the presence of most kinds of organic matter by the smell and separa tion of carbon, and the presence of water by the drops which condense in the cooler part of the tube. Heating on charcoal with a reducing flame,
sometimes with the aid of fluxes, shows the pres ence of metals that give volatile oxides, the latter forming characteristic on the charcoal; and the same test makes it possible to detect any important quantity of an easily reducible nwtal, metals in the free state being readily identified by their lustre and properties. The behavior of the substance when fused with a bead of sodium metaphosphate or of sodium car bonate shows whether a silicate or much silica is present, etc. Often additional special tests are made. For example, gantly warming a small par tion of the substance with concentrated sulphuric acid may serve to detect volatile acidic sub stances, such as sulphurous acid and nitrous acid, which might be lost in the regular processes or appear in another form.
If the substance submitted for analysis is a liquid, its color and odor are noted, its reaction toward litmus is ascertained, a portion is evapo rated to dryness, and the solid residue, if there is any, is subjected to the preliminary examina tion as in the case of any other solid.