ANALYSIS or AI INERALS. The determination of minerals is largely a question of experience gained by the study of large and varied collec tions of specimens. The eye becomes trained by practice to recognize crystallizations even in dis torted and imperfectly exposed forms, to asso ciate certain colors. lustre, and structure with definite species. and to associate certain min erals with certain rock matrix. Several phys ical properties are of considerable aid in identifying questionable specimens. as. for ex ample, the color of the powdered mineral as shown by rubbing it on unglazed porcelain. the approximate relative hardness as determined by scratching the specimen with a knife point, and the relative weight. as roughly determined by weighing the speehnen in the hand. These rough determinations whieli are of particular value as field methods may be supplemented, with the addition of sonic simple and portable apparatus, by determinations of solubility and fusibility. A more detailed examination of the composition of a mineral involves recourse to the blowpipe analysis. Some idea of the results obtained by this form of analysis will be gained by an exami nation of the accompanying plate, \Odell shows the reactions obtained from sonic. of the fusible metals. by heating their compounds with suitable fluxes on charcoal and plaster supports. The coatings of iodides are produced by using a flux composed of two parts sulphur and one part ea eh of potassium bisulphate and potassie iodide. Re actions for iron, copper, manganese, nickel, en halt, ehromium. and other metals are obtained by dissolving small portions of their compounds in hot beads of borax or microeosmic salt and sub jecting, the resulting fusion to the oxidizing and reducing action of the blowpipe flame. The color imparted to the blowpipe flame serves as a test for compounds of calcium, strontium, lithium, barium, sodium, and other elements. These tests as well as others of similar nature merely an notume the presence or absence of au (-lenient the relative when required must be mined by a systematic quantitative analysis.
IlisTonv. Although a few mineral species were known to philosophers at au early date in the world's history. it was not until the development of chemistry from alchemy in the sixteenth cen tury that savants approached the subject of mineralogical knowledge in the true spirit of scientific investigation. As a natural outcome
of the comparatively advaneed state of mathe matical knowledge at the period of this scientific awakening, the subject of crystallization early developed a marked importance. In 17S3 De lisle, with the aid of a primitive form of goni °meter, measured the interfacial angles of a num ber of crystals and established the law of con stancy of interfacial angles. The Abh6 Ilaily about the same time developed a theory corre lating the internal structure of crystals with their outward form. lie practically formulated the law of rational indices which constitutes the corner-stone of crystallography. Haiiy was fol lowed by liaustnatm with his application of spherical trigonometry in 1803, Weiss with a development along purely mathematical lines in 1814, :Mobs with a division of crystals into six systems in Naumann in 1523, and W. IL Aliller in 1830. In recent years the science has made vast strides. and new methods and lines of research are being constantly developed. Our knowledge of the science of mineralogy is con stantly enriched by the discovery of new species, while mining and quarrying operations are con tinually bringing to light new and interesting crystalline forms and varieties of well-known minerals.
Research in physical mineralogy is being ex tended, notably in termany, along a number of lines, and from time to time valuable additions are made to our store of knowledge by careful and exhaustive studies of the optical. thermal. and electrical properties of certain mineral spe cies. A method by which the symmetry of crys tallized minerals may be investigated has been developed by Baundmuer, Beck. and others. This method depends upon the development. of minute angular cavities upon crystal faces by means of the interrupted action of some dissolving medium. The symmetry of these pits, which are known as etch figures. conforms to the crystallographic symmetry of the mineral experimented upon. Of a similar nature in their bearing upon the ques tion of crystal strmture are the percussion fig ures and solution planes which have been made objects of special study by several authors.