usually brown or black. The crystals commonly possess a very brilliant lustre.

Infusible in the forceps; the behavior before the Blp is that of pure oxide of tin (v. Table II, 22), excepting of its sometimes imparting to the Bx bead a slight yellowish tinge, owing to the presence of iron, and exhibiting the reaction for manganese when fused with soda and nitre on platinum-foil.

Insoluble in acids. Fused with caustic potassa, yields a mass which is mostly soluble in water.

Tin Pyrites.

§ 210. 2 Cu'S, SnS2 + 2 (FeS, ZnS), SnS2.

H-4. G-4.3-4.5.

Of steel-gray or iron-black color, and metallic lustre. Occurs usually massive, granular, and disseminated.

In an open glass tube, yields sulphurous acid and oxide of tin, which collects close to the assay-piece and which cannot be volatilized by heat. On Ch in R Fl, fuses to a black scoriaceous globule; in O Fl, gives out sulphurous acid and becomes covered with oxide of tin. When well calcined by the alternate application of O Fl and R Fl, gives with Bx the indications of Fe and Cu. With Sd and Bx, yields a globule of impure copper.

Decomposed by nitric acid; a blue solution is obtained, and a mixture of sulphur and oxide of tin remains undissolved.

ORES OF ZINC.

Red Zinc Ore [Zincite].

§ 211. ZnO, containing some Mn2O3. H=4—4.5. G=5.4—5.5. Of a deep-red color and high lustre ; of distinctly foliated structure. Infusible alone. Dissolved by Bx in O Fl with manganese reaction. With Sd on Ch, deposits a copious Ct of oxide of zinc. Soluble in nitric acid without effervescence; in hydrochloric acid with evolution of chlorine.

Blende.

§ 212. ZnS. H=3.5-4. G=3.9-4.2. Of very variable color, from yellow to black; of resinous lustre and lamellar aspect, distinctly cleavable. It occurs often crystallized in rhomboidal dodecahedrons. The powder is always light-colored, white or grayish,

and dull.

In a matrass, sometimes decrepitates violently, but gives nothing volatile; its color also remains unchanged, excepting the green varieties, which become yellow. Strongly heated in an open glass tube, sulphurous acid is evolved, and the color of the calcined assay is white, yellowish, or brownish, according to the amount of FeS which it contains. Alone, infusible or only rounded at the thinnest edges. On Ch in R Fl a feeble dark Ct of oxide of cadmium is usually obtained, which is soon followed by a pure zinc-Ct. With Sd on Ch, is easily reduced, and the characteristic zinc-flame may frequently be observed. Iron is readily detected by calcining the mineral in the O Fl and treating the residue with Bx.

The pulverized mineral dissolves in nitric acid, leaving a residue of sulphur.

Smithsonite [Calamine].

§ 213. ZnO.CO2. H=5. G=4-4.5. It is found crystallized in forms derived from the rhomboid. Of vitreous lustre, and white, grayish, or brownish color; semi-transparent or opaque.

stalactitic or mammillary.

Often

Heated in a matrass, loses carbonic acid and, if pure, appears after cooling enamel-white. The ZnO is often to a large extent substituted by FeO, MnO, CdO, PbO, MgO, CaO; it then, after cooling, frequently assumes a dark color and gives with fluxes the indications of iron and manganese. Mixed with Sd and exposed to the R Fl, it is decomposed and oxide of zinc deposited on the If the temperature was raised sufficiently high, a zinc-flame is sometimes observable. The Ct is at first dark yellow, or reddish when cadmium is present.

It readily dissolves in acids with effervescence; also in caustic potassa.

Calamine.

§ 214. 3ZnO+SiO3+2HO or 2(3ZnO.SiO3)+3HO. H=4.5—5. G=3.1-3.9. It closely resembles in its physical characters the preceding ore. It is electric by heat; the smallest fragment heated attracts light substances.

Infusible in the forceps. In a matrass yields water and turns milk-white. Bx dissolves it to a transparent glass, which cannot

be made opaque by flaming. It dissolves in S Ph to a transparent glass which becomes opaque on cooling, and in which, when highly saturated, clouds of silica are observable while hot. With Sd on Ch, swells and affords with difficulty a Ct of oxide of zinc. With SoCo, assumes a green color, which, when the heat is raised, passes into a fine light-blue on the fused edges.

It is readily decomposed by acids, with separation of gelatinous silicic acid. Partly dissolved by caustic potassa.

§ 215. C, with a small percentage of SiO3, Al'O3, and Fe2O3. H=2-2.5. G-1.3-1.8. Lustre bright, often sub-metallic; color iron-black, frequently iridescent. Fracture conchoidal.

In a matrass, gives usually a little water, but no empyreumatic oil. Heated on platinum foil in O Fl, is slowly consumed without flame, leaving a small quantity of ash, which consists of SiO3, Al2O3, and more or less Fe2O3. Does not color a boiling solution of caustic potassa.

Bituminous Coal [Common Coal].

§ 216. C, H, O, in variable proportions; the bituminous matter contains from 76 to 90 per cent. of carbon; the earthy impurities consist principally of SiO3, Al2O3, and CaO; contains frequently a small amount of N and FeS2. Softer than anthracite, G=1.2—1.5. Less highly lustrous than the preceding, and of a more purely black or brownish-black color.

In a matrass, some varieties soften and cake (caking coal), while others are entirely infusible; all varieties are decomposed, evolve combustible gases and empyreumatic oils, and leave a residue of more or less metallic lustre (coke), which behaves like anthracite. On platinum foil, burns with a luminous flame and emission of smoke, leaving an earthy residue.

Boiled with a solution of caustic potassa, or with ether, imparts to these solvents no, or only a pale-yellow, color.

Brown Coal.

§ 217. Composition the same as that of bituminous coal, but the organic constituents contain only from 60 to 75 per cent. of carbon. In physical proportion bears sometimes a close resemblance to the preceding; some varieties show distinctly the texture of wood (lignite).

In a matrass, infusible, but some varieties soften; evolves combustible gases, empyreumatic oils, water of acid reaction, and a peculiar disagreeable odor, leaving a residue which consists of carbon and a considerable amount of ash. On platinum foil, burns with a smoky flame and emission of a peculiar odor.

Boiled with a solution of caustic potassa, colors the liquid brown. Asphaltum.

§ 218. C, H, O, in variable proportions, with about 75 per cent. of carbon. G=1-1.2. Of black or brownish-black color, and

bituminous odor.

Fuses at about 100° C, and burns with a bright flame and emission of a thick smoke, leaving little ash, which consists essentially of SiO3, Al2O3, and Fe2O3. In a matrass, gives empyreumatic oil, some ammoniacal water, combustible gases, and leaves a carbonaceous residue.

Treated with boiling ether, colors the solvent wine-red to brownish-red (distinction from bituminous coal); treated with a boiling solution of caustic potassa, does not color the liquid, or imparts at the most a pale-yellow color (distinction from brown-coal).

FIFTH CHAPTER

SYSTEMATIC METHOD FOR THE DISCRIMINATION OF INORGANIC COMPOUNDS.

THE careful observer, having become well acquainted with the reactions which are exhibited by the metallic oxides and other simple compounds, when subjected to the various treatments detailed in the second chapter, will find no difficulty in ascertaining the nature of any mineral substance presented to him for analysis.

If the reactions are not quite distinct, owing to an intermixture with other substances, he may call to his aid the processes laid down in the third chapter, which will enable him, in most cases, to detect also the nature of the impurities. But in order to attain satisfactory results in this way, a certain familiarity with all the principal tests is a necessary condition; this once acquired, any further directions are quite superfluous.

Those, however, who have not devoted much time to blow-pipe operations, will sometimes experience some difficulties in drawing the correct conclusions from the observed phenomena, a difficulty which is to a great extent obviated by pursuing the course given below. This methodical course has the advantage of giving the operator the answer to every phenomenon which he observes, and thus leading him, though sometimes by a very tortuous path, to the right solution. An example will show this more clearly, and teach at the same time the use of the table.

Suppose a substance be given for analysis. The operator commences with No. 1. The substance is heated in R Fl on Ch: a garlic odor is disengaged; proceed to No. 2. Treated with Sd on Ch does not give a mass which exhibits the reaction of sulphur; proceed to No. 3. The substance shows no metallic aspect; proceed to No. 131, thence to No. 135. It is not wholly volatilized, nor does it exhibit the reaction of sulphur; proceed to No. 137.