the addition of 8 c.c. of concentrated sulphuric acid until fumes of sulphuric acid are copiously evolved.

The sulphates are dissolved in water and transferred to a 180 c.c. tall beaker, keeping the volume of the solution about 50 c.c. Sixty c.c. of ammonia, sp. gr. 0.9 is gradually added to the solution in the beaker (kept cool in running water) followed by 10 c.c. of 20 per cent. ammonium bisulphite solution.

The cobalt and nickel are deposited together with a current of 2.5 amperes. When the solution is colourless, the cover glass and the sides of the beaker are rinsed with water, and the current, reduced to 0.5 amperes, is allowed to pass until a few c.c. of electrolyte tested with potassium sulphocarbonate show that the cobalt and nickel are completely deposited. The cathode is removed with the usual precautions, dried, and the deposited cobalt and nickel weighed.

The cobalt and nickel are dissolved from the cathode with 30 c.c. of nitric acid (1:3), the cathode rinsed, removed, and the solution of the metals boiled to expel nitrous fumes. The solution is diluted to 500 c.c., neutralized with ammonia, made faintly acid with nitric acid, heated to about 50 to 60°C. and the nickel precipitated with a 1 per cent. alcoholic solution of dimethylglyoxime, followed by 10 c.c. of a 20 per cent. ammonium acetate solution.

The precipitate is allowed to stand for four hours, filtered on asbestos, washed twice with hot water, re-dissolved, and the precipitation repeated in a volume of 200 c.c.

After standing for an hour in a warm place, the nickel precipitate is filtered into a Gooch crucible, washed with hot water, and dried at 130 to 140°C. for forty-five minutes. The weight of the precipitate multiplied by 0.20316 gives the nickel. The amount of cobalt is found by difference.

Notes and Precautions.-Cobalt metal usually contains from 98 to 98.5 per cent. cobalt plus nickel. For this reason the amount of 0.2 to 0.3 grams of material recommended by some for the determination of the cobalt and nickel seems scarcely sufficient, as the weighing errors involved would appreciably affect the results. The use of large quantities of acids for solution and oxidation is to be condemned, as the removal of the excess consumes time and increases the chances of mechanical loss.

The separation of iron as basic formate is preferred on account of the ease with which it can be washed, and the formates are completely decomposed on evaporation with sulphuric acid.

The presence of acetates in the electrolyte seems to retard the complete deposition of the last traces of nickel. In one instance on electrolyzing a solution from metal containing 97.5 per cent. of cobalt and 0.8 per cent. of nickel, in the presence of acetates one milligram of nickel was found in the electrolyte 30 minutes. after complete deposition of the cobalt. The volume of the electrolyte should be kept within the limit specified above, as the complete deposition of the metals from dilute solutions is unnecessarily prolonged.

It has been found that the amount of cobalt and nickel remaining in the electrolyte after electrolysis is less than 0.01 per cent. on a one gram sample.

The cathodes used are of the perforated type with an effective surface of 90 square centimetres. The anodes are spirals made of 0.04 inch wire, 0.6 inch diameter, and have about 6 turns.

Dry Assay for Nickel and Cobalt 1

In this assay advantage is taken (1) of the facility with which nickel and cobalt may be concentrated in combination with arsenic to form a speiss; (2) of the order of oxidation of the metals which the speiss may contain, viz., iron, cobalt, nickel, and copper, and the colours they impart to borax. They are removed in the order named. Iron gives a brownish colour to borax, cobalt a blue, nickel a sherry-brown, and copper a blue. Hence, on scorifying the speiss with borax, the colour imparted by the oxide produced indicates the metal being removed. By careful and frequent examination of the colour resulting and the renewal of the borax it is possible to find the point at which first the iron and then the cobalt and nickel are removed. A greenish tint is imparted to the borax at the moment the cobalt begins to scorify, succeeded by a full blue (with fresh borax), followed by a greenish tint when the nickel commences to pass out. This changes to the full sherry-brown, and is followed by a greenish tint when copper commences to oxidize.

Careful examination and much care are necessary to obtain even fair results. By weighing the button at the various stages, the proportion of its constituents may be determined. If copper be present, 1 gram of gold is added to the button after the removal of the cobalt.

Assay of Ores and Speiss.

From 5 to 25 grams of the ore are finely powdered and passed through an 80-mesh sieve and calcined "sweet." At the end of the roasting some finely ground anthracite must be added, and the calcination continued till the carbon is burnt away, thus reducing the sulphates and arsenates formed in the earlier stages.

The roasted mass is mixed with 0.2 to 0.5 times its weight of arsenic, an equal weight of carbonate of soda, 5 grams of argol, and 2 to 4 grams of borax, melted in a crucible at a moderate temperature, and poured. If iron be absent, 0.5 grams of pure iron filings must be added before fusion.

When cold, the button is detached from the slag and weighed. It should be metallic in appearance, and have a smooth grey surface. Portions weighing 1 gram should be taken for the subsequent scorification.

The scorification with borax is conducted in small shallow dishes 3/4 inch in diameter inside and inch deep. These may be made of finely-sifted clay and ground pots. The clay should be stiff, and as much pressure as possible used in shaping them. The die may be made of boxwood, and provided with a gun-metal or iron ring. The dishes should be dried carefully and heated to dull redness in a muffle before use.

While preparing the speiss, a small muffle should be made as hot as possible, as the success of the operation depends largely on the temperature. The back of the muffle should be white-hot. Place a number of the small dishes in the muffle. Have at hand some ground borax glass, and a vessel of cold water. Place about a gram (rather less than more) of borax in one of the dishes as far from the front as can be seen. It is convenient to wrap the borax in tissue paper and drop in the speiss, also wrapped in tissue paper.

The muffle should be hot enough to melt the speiss immediately, or the order of oxida tion will not be preserved. The borax should not be sufficient to cover the speiss when melted. For a moment the surface is dull, but almost instantly brightens and scorifies, very much like the brightening stage in the cupellation of silver. In a few moments remove the dish and contents, and immediately place the bottom of it in water to cool, and as soon as the bead is solid, submerge it in the water.

If iron only has passed off, the brownish-yellow tint due to that metal will only be observed, but if the smallest amount of cobalt has been removed the slag will be greenish or, if a larger quantity, blue. The correct stage has been reached when a faint green tinge is visible in the slags near the edge and round the button. If this be not observed, the operation is repeated till the point is reached. If it is past, the scorification is re-started with a fresh portion of speiss.

The speiss now only contains cobalt, nickel, and copper. It is weighed, and the operation repeated with every precaution till the cobalt is removed. Less borax is necessary as the bead is reduced in size, and a green cap of arsenate appears when the nickel commences to oxidize, as well as the greenish tinge in the slag near the bottom. The attainment of this point is marked also by the motion of the button momentarily ceasing. The process needs careful watching. The dish is withdrawn, and quenched carefully as before. If, on examination, it is doubtful whether the nickel has commenced to scorify, it is best to weigh the prill and return it to a scorifier with fresh borax, and examine immediately it is melted. The dense blue of the cobalt will not then interfere, and the brownish colour of the nickel (and the green cap) will be apparent. The prill is weighed. If copper were present in the speiss, the prill will now consist of nickel and copper arsenides. If much nickel is present the scorification may be continued in the same manner, but it is better to add 1 gram of pure gold, and continue the scorification so long as nickel continues to be removed. The resulting Assaying and Metallurgical Analysis, pp. 193-195, Rhead and Sexton; Longmans, Green and Company, 1911.

bead consists of the added gold and copper. It is weighed, and the increase in weight of the gold bead gives the copper. Confirmatory results may be obtained by cupelling the goldcopper bead with 34 times its weight of lead, when the gold only will be left, the loss of weight being copper.

In the above remarks it has been assumed that cobalt is present. If it is absent, it is difficult to ascertain the point at which iron is removed and nickel commences to pass out. Further, in assaying an unknown speiss, which may contain nickel and iron only, the green arsenate of nickel which forms on the surface and under the bead must not be confounded with the green tinge indicated above.

Modified Method.

In order to avoid the difficulty caused by the copper, it is sometimes removed before forming the speiss.

The sample of ore is digested with aqua regia till completely decomposed, hydrochloric acid added, and the nitric acid expelled by evaporation. Water is then added, and the liquor saturated with sulphuretted hydrogen, which precipitates the copper, etc. The liquid is filtered, and the residue washed with water containing sulphuretted hydrogen.

The filtrate is then boiled till sulphuretted hydrogen is completely expelled, oxidized by adding a few drops of nitric acid to the boiling solution and neutralized. To the neutral solution barium carbonate and bromine water are added in excess and well shaken. After boiling, the solution is filtered, and the precipitate washed, dried, and ignited. This precipitate, which contains the whole of the iron, cobalt, and nickel, is converted into a speiss as before, but without roasting.

Additional References

Aaron, Process of Precipitating Nickel and Cobalt from Solutions. The metals are precipitated as methyl sulphocarbonates; United States Patent, No. 330,454, Nov. 17th, 1885. Grossmann and Schueck, Dycyandiamide in the Determination and Separation of Nickel. Engineering and Mining Journal, Vol. LXXXV, 1908, p. 1044.

Schoeller and Powell, The Determination of Nickel and Cobalt by the Phosphate method. The Analyst, Vol. XLI, 1916, pp. 124-131; Vol. XLII, 1917, pp. 189-199. Chem. Abst.. Vol. XI, 1917, p. 2437.

Schoeller & Powell, The Determination of Cobalt and Nickel in Cobalt Steel, Jour. Iron & Steel Inst., Vol. XCVII, No. 1, 1918, pp. 441-449.

Powell, The Estimation of small quantities of Cobalt. Jou. Soc. Chem. Ind., Vol. XXXVI, 1917, pp. 273-274.

Walker, Separation of Nickel and Cobalt by Red Lead. Eng. Min. Jour., Vol. 103, 1917, p. 894.

The Use of Dimethylglyoxime as an Indicator in the Volumetric Determination of Nickel by Frevert's Method, Jour. Ind. Eng. Chem., Vol. 8, 1916, pp. 804-807.

Metzl, The Volumetric Estimation of Cobalt in the Presence of Nickel, Zeitschr. Anal. Chemie, Vol. 53, 1915, p. 537.

CHAPTER IV

THE USES OF COBALT

Cobalt Oxide

Cobalt is used chiefly in the form of oxide in the enamel, porcelain, and glass industries, but within the last few years new uses have been found for the metal which is at present produced in considerable quantity. Cobalt metal is used chiefly in the manufacture of stellite, a cobalt-chromium alloy, used as a cutting tool. The metal is added to some high-speed steels to give improved cutting qualities. It is also used in cobalt plating.

Cobalt oxide and its compounds are used as pigments or colouring agents. It is said that when cobalt oxide is present in the ratio of 1:20,000, it imparts a bluish tinge to clear glass or porcelain. The oxide is black or gray, but when fused with borax or silica it possesses a brilliant blue colour. Cobalt oxide is also used in small proportions to produce white enamels, since any yellow colour due to iron oxide is neutralized by the complementary cobalt blue, producing a pure white. Also by the addition of cobalt oxide, copper oxide, pyrolusite, and even iron oxide, to certain raw mixtures or waste enamels, a beautiful black enamel is obtained. The compounds of cobalt, for example, silicate, aluminate. phosphate, arsenate, and nitrite are used instead of the oxide, because they give better and more uniform colouring. The following table gives a list of the customary brands of cobalt compounds with their cobalt content:

Theoretically CoO, Co.О, and Co ̧O, contain 78.8, 71.1, and 73.4 per cent cobalt, respectively. The history of the value of cobalt compounds as colouring agents dates back to pre-historic times. However, it may be stated that it was not until the discovery of the silver-cobalt deposits at Schneeberg in 1470, that cobalt was used to any great extent. The preparation of cobalt compounds must have been carried on in a small way because about the year 1790, there were 25 works engaged in the industry, most of which were located in Saxony, and the total production of these works was not more than 300 tons of cobalt annually, which was mostly in the form of smalt. The smalt which contained approximately 6 per cent, cobalt was sold in Venice in 1520 at about 16 cents a pound. There were also a few refineries in Holland which supplied the Irish linen trade almost entirely. as well as a large amount to the linen industries at home. It was also used in Holland in the manufacture of litmus. A complete description of the early history of the cobalt industry in Saxony, is given by Mickle in the Report of the Bureau of Mines of Ontario, vol. XIX, 1913, Pt. II, pp. 234-251.

At present the ceramic industry is carried on chiefly in the United States, Germany, France, and Austria-Hungary. In Germany and Austria-Hungary it gives employment to 50,000 people.

Smalt is used now only in a few enamel works. It is a blue compound which owes its colour to the presence of cobalt silicate. As formerly prepared it contained appreciable quantities of impurities. The oxides of cobalt are preferred to smalt because of their purity, uniformity, and lower cost.

The arsenate is prepared by adding sodium arsenate to a cobalt nitrate solution.

Cobaltous carbonate is obtained by adding soda or potash to a solution of a cobalt salt. The rose coloured precipitate which forms is a basic carbonate, of the formula CoCO2+Co(OH)..

Cobalt phosphate is prepared by adding sodium phosphate to a cobalt acetate solution. The precipitate is violet in colour and has the formula Co. (PO4)2.

The aluminate is formed by adding sodium carbonate to a mixture of cobalt nitrate and alum. The cobalt and aluminium hydroxides may be precipitated separately and afterwards mixed. The mixed hydroxides are washed, dried, and heated at a red heat. The blue cobalt aluminate which forms is ground and dried.

The colour produced by the aluminate, phosphate, or arsenate has various names, for example, cobalt blue, cobalt ultramarine, king's blue, Thenard's blue, or azure blue. Thenard's blue corresponds to cobalt aluminate. Coeruleum, coeline, or blue celeste, is a blue colour showing a slightly greenish tint. It contains oxide of tin and sometimes calcium sulphate. To prepare such a pigment, sodium stannate is added to a cobalt nitrate solution. The precipitate is washed and heated. Another method to prepare blue celeste is to heat cobalt sulphate, tin oxide, and precipitated silica or chalk.

Mazarine blue is commonly employed as a band on the edges of plates. The colour is prepared by mixing cobalt oxide, with tin oxide, sand, and calcium sulphate.

New blue is a pigment varying in colour from a pale greenish blue to a deep turquoise blue. It is largely used for enamels, and consists of aluminates of cobalt and chromium produced by the action of alum on carbonates and hydrates of cobalt and chromium.

Cobalt green or Rinmann's green is formed by substituting zinc oxide for alumina in cobalt aluminate, giving cobalt zincate. This compound may also be formed by mixing the hydroxides or oxides or by adding soda to a cobalt-zine solution. In either case the oxides must be heated to form the zine compound. The darker green colours contain the smaller quantities of zinc. A mixture of calcined cobalt carbonate, chromium oxide, and alumina also produces a green pigment.

Cobalt bronze is a cobalt ammonium phosphate compound. It has a violet colour with a bronze-like metallic lustre.

Cobalt yellow, Indian yellow, aureolin, is the precipitate potassium cobaltic nitrite. It is prepared by adding potassium nitrite to a cobalt solution acidified with acetic acid. It is a bright yellow precipitate which because of its purity produces an excellent colour.

1

Mellor, Clay and Pottery Industries, 1914, p. 71, Lippincott, Philadelphia.