caoutchouc tube b, so that glass touches glass. The flask is now slowly heated over a spirit-lamp, so as to avoid the passage of liquid from d back into a. The heating is continued until the greenish color of the chlorine in the bulb of the connecting tube disappears, the ore is entirely decomposed, and a peculiar crackling noise is heard in the flask. The heat is somewhat increased for about half a minute after the crackling noise has been perceived, to prevent the liquid, containing about 5 grammes (77.16 grains) of solid potassium iodide and colored brown by the separated iodine, from passing over into the flask. The gas-conducting tube c is then withdrawn from the retort with the left hand, the heating of the flask a being continued all the while by holding the spirit-lamp below it with the right hand (if these manipulations are not conducted with proper skill, there is danger that the liquid in the retort will pass over). The tube is then washed off in a beaker-glass. The retort, containing the brown iodine solution, is corked, and carefully shaken, so that the solution may take up all the free iodine, during which operation the liquid must not come in contact with the cork. After the fluid has become entirely cold, it is poured out in the beaker-glass. Should the liquid contain any undissolved iodine, a few crystals of potassium iodide must be added before the contents of the retort is emptied into the beaker-glass. It is then diluted to the bulk of one-half liter (0.88 pint). 100 cubic centimeters (6.1 cubic inches) of this are taken, introduced into a separate vessel, and titrated sodium hyposulphite is added to it as long as a red color is still distinctly perceptible. About 2 grammes (30.87 grains) of starch liquor are added, and then more sodium hyposulphite, drop by drop, until the blue color which has been formed just commences to disappear. If necessary, the assay may be controlled

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

Fig. 62.

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 solu

tion.

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

'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+2FeCl1⁄2= Fe2C14). 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 permangaIn 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.

nate.

XVIII. SULPHUR.

72. ORES.

Native sulphur (sulphur earths); iron pyrites, FeS2, with 53.33 S and 46.47 Fe; magnetic iron pyrites, 5FeS.FeS, 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. (Cu2S+ FeS = CuS+2FeS+S).

1 Dingler, ccxxx. 66.

17

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 manufacture of sulphuric acid, or its yield of sulphur for the formation 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 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.