times the quantity of calcined sodium carbonate, with a thick covering of these fluxes. When the crucible is cold, the potassium arseniate is extracted by lixiviation with hot water, and evaporated to dryness with nitric acid. The dry mass is treated with water, the silicic acid filtered off; the filtrate is treated with ammonia in excess, then with a solution of magnesium sulphate (or at once with magnesia mixture prepared from 110 parts of crystallized magnesium chloride, 700 parts concentrated ammonia, 140 parts ammonium chloride, and 1300 parts water). The liquid is allowed to stand for 12 hours, the ammonium-magnesium arseniate, 2(MgN H. AsO1 ̧)+H2O, is filtered off upon a filter previously dried at 100° C. (212° F.), and weighed; 100 parts of salt dried at 100° C. (212° F.) and weighed, will contain 60.51 parts of arsenic acid, corresponding to 65.21 per cent. of arsenic and 86.08 per cent. of arsenious acid. By igniting very carefully and not too quickly, the magnesium salt passes into Mg, As2O7. Or the sample is digested in strong nitric acid with the addition of a few crystals of potassium chlorate. The solution is diluted with water and filtered. Some lead nitrate in solution is added to the acid liquid, when lead sulphate will be separated, lead arseniate remaining in solution. The precipitate of lead sulphate is filtered off, the filtrate saturated with soda, when the lead arseniate will be separated. This is filtered off, washed, dried, and weighed. 100 parts arseniate= 22.2 parts of metallic arsenic, or 29 parts of arsenious acid.

2. Wet method combined with the dry-1 to 1 grammes (15.43 to 23 51 grains) of the substance is fused in the manner indicated under 1, with saltpetre and sodium carbonate, in order to obtain a solution of alkaline

1 Plattner-Richter's Lōthrohrprobirkunst, 1878, p. 651.

arseniate. The filtrate is saturated with nitric acid, and strongly diluted in case sulphuric acid is present. Silver nitrate in excess is then added, and sufficient ammonia to cause the precipitate to disappear. The excess of ammonia. is evaporated without boiling until its odor has disappeared. The silver arseniate is then filtered off, dried, and smelted with lead, and the arsenic calculated from the quantity of silver found, 1 atom of arsenic being precipitated to 3 atoms of silver, or 100 silver corresponds to 23.15 arsenic 35.5 arsenic acid.

B. Volumetric assays.-The method most used is T Mohr's estimation of arsenious acid; according to which arsenious acid combined with soda is completely converted into arsenic acid by iodine (As2O3+212+2Na2O = 4NaI+As2O).

=

A solution containing in 500 cubic centimeters (30.5 cubic inches) 2.5 grammes (38.58 grains) of iodine and 4 grammes (61.73 grains) potassium iodide, or in 1 c. cm. 0.005 gramme (0.077 grain) of iodine, is added to a solution containing sodium arsenite, sodium bicarbonate, and some starch paste. Fixing of the standard: 4.95 grammes (75.38 grains) of arsenious acid are placed in a flask and dissolved in sodium bicarbonate, in about 200 cubic centimeters (12.2 cubic inches) of water. The clear solution is poured off, and sodium salt and water are added in small portions until solution is complete. It is then transferred to a liter flask, 20 to 25 grammes (308.64 to 385.80 grains) more of sodium bicarbonate. are then added, and the flask is filled up to the mark. 10 c. cm. of this solution are taken, some fresh starch solution and sodium bicarbonate added, the liquid diluted to about 150 c. cm., and then titrated with the solution

1 Mohr, Titrirmethode, 1874.

of iodine until the blue color appears, which must not disappear even when sodium bicarbonate is added. Arsenic acid must be reduced to arsenious acid by introducing sulphurous acid gas into the hot acid solution, or by the addition of sulphites.

XV. URANIUM.

66. ORES.

Pitch blende, UrOg, with 84.9 Ur.

67. WET ASSAYS.

Namely:

A. Gravimetric assays.

1. More accurate analytical process.-1 to 2 grammes (15.43 to 30.87 grains) of ore, etc., are decomposed with concentrated nitric acid. The solution is diluted and the residue and precipitate (silicic acid, lead sulphate, basic antimony and bismuth salts) are filtered off. The arsenic acid in the filtrate is reduced by means of sulphurous acid to arsenious acid, and the sulphurous acid removed by boiling. It is then precipitated with sulphuretted hydrogen (As, Sb, Pb, Bi, Cu), filtered, and the sulphuretted hydrogen removed by boiling. The iron is then oxidized by potassium chlorate, ammonium carbonate in excess added, and the liquid filtered. Ammonium sulphide is now cautiously added in the cold in order to precipitate Mn, Zn, Ni, Co, leaving the uranium in solution. The liquid is then filtered, and the filtrate heated with nitric acid to separate sulphur. It is now again filtered, and when the solution has become cold, the uranium is precipitated, as brownish-yellow ammonio-uranic oxide,

by ammonia. This is filtered off, washed, dried, and ignited to green uranoso-uranic oxide (UrO2.2UrO, = Ur,O), with 84.8 uranium, corresponding to 96.22 uranous oxide (UrO2) and 101.9 uranic oxide (UrO3).

2. Patera's technical test.-5 grammes (77.16 grains) of ore are dissolved in nitric acid, not in excess. The unfiltered solution, which has been freed from the excess of nitric acid by boiling, is super-saturated with sodium carbonate, boiled for a short time, and the solution containing the sodic-uranic carbonate is filtered into a golden dish. The solution is evaporated to dryness, the residue ignited and extracted with hot water, and the insoluble acid sodium uranate (Ur,Na2O,) is filtered off, ignited, and weighed. 100 parts of the weight obtained equals 88.3 parts of uranoso-uranic oxide.

In case a golden capsule should not be at hand, the solution of the uranic oxide in soda is treated with sodium hydrate in order to precipitate hydrated acid sodium uranate. It is then filtered, washed, and dried, and the precipitate is removed as much as possible from the filter and ignited together with the ash of the filter. It is then again washed upon the filter and dried and ignited. In case a considerable quantity of copper is present, a small quantity of it passes into the alkaline solution.

B. Volumetric assay.-1 to 2 grammes (15.43 to 30.87 grains) of ore is dissolved in concentrated sulphuric acid. The sulphuric acid (not hydrochloric acid) solution is diluted according to the richness of the ore, to

or liter (0.88 to 0.44 pint). 50 cubic centimeters (3.05 cubic inches) of this are taken, placed in a suitable flask, and diluted with 100 cubic centimeters (6.1 cubic

Dingler, clxxx. 242 (Patera). Fresenius' Ztschr. v. 229 (Fresenius); viii. 387 (Winkler).

2 Journ. f. prakt. Chem. xcix. 231 (Belohoubeck). Fresenius' Ztschr. xi. 179; xvi. 104.-Gouyard's Probe in Chem. Centr. 1864, p. 339.-Analyse der Uranoxydalkalien in Fresenius' Ztschr. iii. 71 (Stolba).

inches) of water. The liquid is boiled for half an hour with zinc until the yellow solution of uranic oxide has assumed the sca-green color of uranous oxide. All the zinc is dissolved, and the uranous oxide is titrated with potassium permanganate (p. 127). Uranous oxide requires the same quantity of potassium permanganate to become oxidized, as ferrous oxide.

XVI. CHROMIUM.

68. ORES.

Chrome iron ore, Cr2FeO4, with 30 to 65 CrO3; cro‐ coisite (red lead ore), Pb.CrO4, with 30.96 CrO3.

69. WET ASSAYS.

Volumetric assays are less frequently made use of than gravimetric assays, and the latter vary, especially in the manner in which the very difficultly decomposable chrome iron-ore is decomposed.

A. Gravimetric assays.1

1. Direct assay.-According to Pourcel's method: 2 grammes (30.87 grains) of the ore in coarse powder are highly heated in order to facilitate its comminution. It is then ground in an agate mortar, or on a porphyry plate, to an impalpable powder, which should show no glistening particles. This powder is heated to 120° C. (248° F.) until it loses no more in weight, and then a sample

1 Journ. f. prakt. Chem. lvii. 256 (Calvert). Fresenius' Ztschr. i. 497 (O'Neill, Oudesluys, Genth); iv. 63 (Souchay); 1861, p. 34 (Mitscherlich); 1870, p. 71 (Storer). Polyt. Centr. 1856, p. 701 (Hart). Dingler, exciii. 33 (Clouet); cxcvii. 503 (Britton); ccxxi. 450 (Dittmar); ccxxiv. 86 (Fels). Bullet. de la soc. de l'industr. minér, St Etienne, 1878, livr. iv. p. 867. (Pourcel).