QUALITATIVE ANALYSIS OF INORGANIC SUBSTANCES.
In the qualitative analysis of inorganic sub stances, the color that a given compound com municates to the flame of a Bunsen burner often affords useful information as to the na ture of the compound, and a systematic exam ination of the substance in the flame of the blowpipe may afford much additional informa tion. (See BLOWPIPE ANALYSIS). When the .substance is partially volatilized in the flame of the Bunsen burner, or by the electric spark from an induction coil, and the light of the flame (or the spark) is examined through the spectroscope, many of the elements can be rec ognized, even when present in exceedingly small quantities, by the occurrence, in the spectrum, of certain characteristic bright lines, or groups of such lines. (See SPECTROSCOPY). The usual method employed, however, for the detection of the commoner bases and acids, is known as the "wet process,° and consists in bringing the substance into solution, and noting the behavior of this solution when certain reagents are added to it. Even in the analysis of inorganic sub stances (which are alone considered in the pres ent section) troublesome combinations some times occur, and in such cases the reaction that might naturally be expected at a certain stage in the examination may be modified to a consid erable extent, or even be suppressed altogether. An adequate account of conditions of this sort cannot be given in the present article, and they are not stated with any degree of completeness in the more elementary manuals on inorganic analysis. Good accounts of the various diffi culties of this sort will be found, however, in Douglas and Prescott's 'Qualitative Chemical Analysis,' to which the reader is referred. The -existence of difficulties and limitations being recognized, a general scheme for the detection of the commoner metallic elements may be given, which will be found to work satisfactorily in the majority of cases.
The first step in making an analysis in the wet way is to ensure the absence of organic matter, which might seriously interfere with the subsequent reactions. If organic matter be
present, it may usually be detected by heating a part of the compound in a closed tube. If it blackens, or gives off a characteristic empyreu made odor, organic matter is probably present, and it must be destroyed either by the continued application of heat, or (if there appears to be danger of losing any essential part of the -inorganic substance by volatilization) by warm ing it with strong sulphuric acid. The organic matter being destroyed by either of these meth ods, the next step is to bring the substances into a state of solution. Water, either cold or hot, should first be tried as a solvent. If this does not suffice, hydrochloric acid, nitric acid or alkaline solvents may be tried. If these reagents fail to effect solution, one part by weight of the substance may be mixed with five parts of sodium carbonate and five of potassium car bonate, and the whole heated in a porcelain crucible until quiet fusion is attained. (This may take 30 minutes). The crucible and its contents are then allowed to cool, and are im mersed in dilute hydrochloric acid, or (if silver is suspected to be present) in dilute nitric acid. In this way most of the commoner insoluble substances may be brought into a state of solu tion. For methods that are applicable to sub. stances that resist this mode of treatment, the more advanced treatises on analysis must be consulted. In case a part of the substances to be analyzed dissolves in water or in one of the other solvents, a separate examination of the solution so obtained should be made, the insol uble part being reserved for subsequent treat ment, by the method indicated above.
The commoner metals (which are the only ones that can be considered in the present article) may be divided into seven general groups, according to their behavior when treated with certain reagents that are known as "group reagents.° These classes or groups are as follows: 1. Metals forming chlorides that are insol uble in water, and which are precipitated as chlorides upon adding hydrochloric acid to their solutions. (Silver, lead and mercurous cury).