Fig. 62. by titrating back with a normal solution of iodine, until the blue color appears again. The standard solution of sodium hyposulphite is prepared by dissolving 24.8 grammes (382.72 grains) of sodium hyposulphite in water, and diluting the solution to 1 liter (1.76 pints). 0.1 to 0.2 gramme (1.54 to 3.08 grains) of pure iodine is then dissolved in 18 grammes (277.78 grains) of potassium iodide, free from iodic acid, and this solution is also diluted to 1 liter (1.76 pints), when 1 cubic centimeter (0.061 cubic inch) of normal solution of sodium hyposulphite will correspond to 0.0127 gramme (0.19 grain) of iodine contained in 1 cubic centimeter (0.061 cubic inch) of solution, so that equal volumes correspond. Fig. 62 represents a modified form of this apparatus, in which the bulbed-tube attached to the dissolving flask passes into a long and narrow tube, which is cooled by immersion in cold water, and contains a higher column of potassium iodide solution. 2. Levol's method with iron.'-0.5 to 0.6 gramme (7.71 to 9.26 grains) of manganese ore, and 0.8 to 1 gramme (12.35 to 15.43 grains) of piano wire (containing on an average 99.6 per cent. of pure iron), are treated with ex 1 Dingler, lxxxv. 299 (Levol) ; cxcvii. 422 (Pattinson). Fresenius' Ztschr. 1869, p. 509 (Teschemacher u. Smith). clusion of air with hydrochloric acid, in a flask provided with a rubber valve (Fig. 10, p. 39); when, from the resulting ferrous chloride, a quantity of ferric chloride corresponding to the chlorine developed will be formed (MnO2+4HCl=MnCl2+2C1+ 2H2O and 2C1+2FeCl2= Fe,Cl). The liquid is diluted to 0.5 liter (0.88 pint). 100 cubic centimeters (6.1 cubic inches) of this are taken, and, after having become entirely cold, the non-oxidized quantity of ferrous oxide is determined by titration with potassium permanganate (p. 127). The quantity of iron. oxidized by the chlorine is determined from the difference; and 2 atoms of iron (112) correspond to 1 atom of manganese peroxide (87.14). Ammonio-ferrous sulphate, FeSO,+(NH,),SO,+6H,O, may be used instead of metallic iron, in the proportion of about 7 grammes (108.02 grains) to 1 gramme (15.43 grains) of manganese ore with 70 per cent. of peroxide, and 8 to 9 grammes (123.46 to 138.89 grains) if the percentage is higher; when 2 atoms of the salt (784) correspond to 1 atom of manganese peroxide (87.14). The assay solution to be titrated should be cold, and strongly diluted, to prevent the hydrochloric acid from being decomposed by the potassium permanganate; or, potassium bichromate1 may be used instead of potassium permanganate. In this assay (iron test), which is much used in England, a part of the chlorine is consumed for the higher oxidation of the ferrous oxide, if any be contained in the ore. XVIII. SULPHUR. 72. ORES. Native sulphur (sulphur earths); iron pyrites, FeS2, with 53.33 S and 46.47 Fe; magnetic iron pyrites, 5FeS. Fe2S3, with 39.5 S; copper pyrites, CuFeS2, with 34.89 S. 1 Mohr, Titrirmethode. 1874, p. 632. Polyt. Centrbl. 1871, p. 1117; Oxalsäureprobe in Fresenius' Ztschr. 1870, p. 410. 73. ASSAYS BY DISTILLATION FOR THE DETERMINATION OF THE AMOUNT OF SULPHUR WHICH AN ORE MAY YIELD. a. Sulphur earths.—0.5 to 1 gramme (7.71 to 15.43 grains) of the ore is heated to a strong red heat in an impervious clay retort, on the neck of which is luted a porcelain tube (Figs. 35, 36, p. 63), when the sulphur vapors will deposit themselves in the porcelain tube, the end of which just dips in water. The tube is then removed and the sulphur collected, dried, and weighed. Gerlach' conducts superheated steam into a glass retort containing the ore, from the neck of which the sulphur, which passes over, drops into a dish containing water. b. Iron pyrites.-2 to 5 grammes (30.87 to 77.16 grains), preferably mixed with the same volume of quartz or powdered charcoal to prevent caking, are placed in a glass tube 30 to 40 centimeters (11.8 to 15.74 inches) long and 13 to 15 millimeters (0.51 to 0.59 inch) wide, closed at one end. The other end is introduced into another glass tube, also closed at one end, and the substance is then heated in a combustion furnace (Fig. 58, p. 230), or by another source of heat (p. 62). The end of the tube containing the sublimed sulphur is cut off and weighed. The sulphur is then volatilized by heat and the tube again weighed. Pure iron pyrites gives on a large scale at the utmost 23 per cent. of sulphur (7FeS 6FeS. FeS2 + 6S); copper pyrites not more than 9 per cent. (Cu,S+ FeS = = Cu2S+2FeS+S). 1 Dingler, ccxxx. 66. 74. ASSAYS OF SULPHUR FOR THE DETERMINATION OF THE QUANTITY OF SULPHUR CONTAINED IN A SUBSTANCE. These assays may be executed in order to determine the yield of an ore in sulphurous acid, for the manufac ture of sulphuric acid, or its yield of sulphur for the for mation of raw matt, for controlling roasting, etc. For this the wet method is more frequently used than the dry method. A. Dry assay (raw matt assay).-The object of this assay is to determine the quantity of metallic sulphides, especially iron sulphide, contained in an ore, after the oxidized and earthy, etc. substances mixed with it have been separated by solvent agents. A mixture of 5 grammes (77.16 grains) of ore and 0.5 gramme (7.71 grains) of resin is introduced into a crucible (Fig. 42, p. 67). Upon Upon this is placed 10 to 15 grammes (154.32 to 231.48 grains) of borax, 5 to 10 grammes (77.16 to 154.32 grains) of glass free from heavy metals, a cover of common salt, and a fragment of coal. The charge is fused at a bright red heat in the muffle or wind furnace for 30 to 45 minutes after the "flaming" has ceased. The resulting button of iron sulphide which is brittle and oxidizes and disinte grates quickly, is carefully freed from slag which should be well fused. It is then weighed and broken up in order to recognize the presence of foreign metallic sulphides by the appearance of the fracture. When only iron pyrites are present, this has a fine grain and speiss yellow color; with copper pyrites, brass yellow; with lead and sulphide, grayish and foliated; with zinc blende, radiated or foliated, of a sub-metallic lustre, and blackishgray; with metallic antimony and arsenic, a fine grain and light gray. Hungary If the ores are easily fusible, 5 grammes (77.16 grains) are charged with a flux composed of 2 parts of calcined borax and 1 part of glass free from iron, by placing a mixture of ore and 11.5 grammes (177.47 grains) of flux in the bottom of the crucible, upon this 23 grammes (354.94 grains) of flux, and on the top 8 to 10 grammes (123.46 to 154.32 grains) of common salt. This is fused in the muffle furnace. When the ores are refractory, 1.25 grammes (19.29 grains) are fused with the same flux, and 3.2 grammes (49.4 grains) of a pure easily fusible concentrated pyrite ore, the percentage of matt contained in this being afterwards deducted; or, with 0.25 to 3.5 grammes (3.85 to 54.01 grains) of copper as a collecting agent.— Pribram: 5 grammes (77.16 grains) are mixed with the quantity of a flux consisting of 10 grammes (154.32 grains) of borax, 2 grammes (30.87 grains) of glass, and 0.4 gramme (6.17 grains) of coal dust. The remaining part of the flux is strewn over this, and on top a cover of common salt and fragment of coal. 0.05 gramme (0.77 grain) of copper may be added to the roasted, and as much as 0.2 gramme (3 grains) to unroasted ores. The crucible, with luted cover, is gradually heated to a moderate red heat in an anthracite furnace (p. 56), and then fused for from 30 to 35 minutes at a bright red heat.— Slags with mechanical inclosures of matt are charged in the following manner 30 grammes (462.97 grains) of slag, 20 grammes (308.64 grains) of borax, and 50 grammes (771.61 grains) of glass with a covering of common salt and a fragment of coal. The charge is fused forto of an hour at a bright red heat. B. Wet assays.2 1. Gravimetric assay.-1 gramme (15.43 grains) of ore is decomposed by fuming nitric acid, then nearly all the nitric acid removed by boiling. Hydrochloric acid is now added and heat is applied, when the sulphur will be quickly dissolved (the heating should not be continued too long, or loss will ensue by the escape of sulphuric acid). The solution is then evaporated to dryness, the residue is heated with hydrochloric acid in order to expel the nitric acid (as otherwise the results would be too high). The liquid is now diluted B. u. h. Ztg. 1871, p. 255. |