cubic inches) of nitric acid, and 360 cubic centimeters (21.96 cubic inches) of water, using a stronger galvanic current, giving 120 cubic centimeters (7.32 cubic inches) of water-gases in Volta's apparatus; or, what is still better, the copper is precipitated from an acid solution by sulphuretted hydrogen, and the copper sulphide dissolved in 30 cubic centimeters (1.83 cubic inches) of nitric acid of 1.2 specific gravity. It is then digested until the sulphur shows yellow. 200 cubic centimeters (12.2 cubic inches) of water are added, and the fluid is then electrolyzed. Fig. 51. D Herpin' dissolves 1 gramme (15.43 grains) or more of the assay sample in nitric acid, evaporates nearly to dryness, dissolves in a small quantity of dilute sulphuric acid, and dilutes the solution to 60 to 70 cubic centimeters (3.66 to 4.27 cubic inches). The solution is poured into the platinum dish A (Fig. 51), and the conducting stand B of the dish is connected with the negative electrode, the platinum spiral C with the positive electrode, and the liquid electrolyzed after the funnel D has been placed in position. When the copper has been precipitated, the fluid is poured from the dish. This is rinsed out first with water, and next with alcohol, then dried and weighed, the copper being determined from the increase of weight.-Hampe's method of testing refined copper: 25 grammes of copper are dissolved in a béaker, at a moderate temperature, in 200 cubic centimeters (12.2 cubic inches) of water, and 175 to 180 cubic centimeters (10.68 to 10.98 cubic inches) of nitric acid of 1.2 specific gravity. To this are added 25 grammes of previously diluted sulphuric acid (about 4 cubic centimeters (0.24 cubic inch) more than is required for transforming the nitrate into sulphate). The liquid is then evaporated to dryness in a porcelain dish on the water-bath. The dry mass is heated upon a B. u. h. Ztg. 1875, p. 394. B Dingler, ccxvii. 440. A Fresenius' Ztschr. xiii. 176. B sand-bath until the volatilization of the free sulphuric acid is complete. The dish is then covered, and, after the mass has become cool, 20 cubie centimeters (1.22 cubic inches) of nitric acid are added to it. Water is now allowed to flow gradually into the dish until the entire volume amounts to 350 cubic centimeters (21.35 cubic inches). The silver is removed by the addition of an equivalent quantity of hydrochloric acid. The liquid is electrolyzed in a vessel capable of holding from 400 to 450 cubic centimeters (24.41 to 27.6 cubic inches). The strength of the galvanic current used should be such that 130 cubic centimeters (7.93 cubic inches) of oxyhydrogen gas-it may vary from 90 to 180 cubic centimeters (5.49 to 10.98 cubic inches)—are developed in 30 minutes in the voltameter from diluted sulphuric acid (1:12). The liquid is electrolyzed for about 72 hours, the subsequent manipulations being the same as above described. The presence of small quantities of bismuth in the precipitated copper can be determined by the following process: The copper is dissolved in nitric acid, concentrated hydrochloric acid in large excess is added, and the nitric acid boiled away. The excess of hydrochloric acid is evaporated on the water-bath, a large quantity of boiling water is added, and, after 24 hours, the precipitate, consisting of basic bismuth and copper salts,is filtered off. The filtrate is dissolved in hydrochloric acid, and again precipitated with water. This precipitate is dissolved in nitric acid, and the copper contained therein separated by ammonium carbonate. 3. Determination of the copper in the form of cuprous sulphide. This demands the absence of metals precipitable from acid solutions with sulphuretted hydrogen, and the metallic sulphides of which are not volatilized in a heated current of hydrogen (silver, lead, bismuth, cadmium, antimony, tin). During the dissolving process, lead may be separated by sulphuric acid, antimony and tin by nitric acid; mercury and arsenic sulphide are volatile. In case a considerable percentage of nickel is present, nickel sulphide will be precipitated with sulphuretted hydrogen, which can only be prevented by using a large excess of acid. Bestimmung des Kupfers in kupferhaltigen Kiesen, Abbräuden und ausgelaugten Abbränden in Fresenius' Ztschr. xvi. 335. 1 to 5 grammes (15.43 to 77.16 grains) of the assay sample are decomposed with nitric acid or aqua regia. The residue of sulphur is removed by hydrochloric acid and potassium chlorate. The liquid is then diluted with. water and the silver precipitated with common salt. The solution is then filtered, heated to about 80° to 100° C. (176° to 212° F.), and saturated with sulphuretted hydrogen, the precipitate filtered, after standing about one hour, and quickly washed with hot water. The filter is dried between blotting paper and next quickly in a hot sand bath. The precipitate is detached from it and the filter with the addition of some sulphur incinerated upon the cover of a tared porcelain evaporating dish which contains the copper sulphide. This, after an addition of sulphur (0.5 gramme, 7.71 grains), is strongly heated for about half an hour, while a current of hydrogen or illuminating gas is conducted to it through an opening in the cover, or through a perforated mica plate, which has been placed upon the crucible. CuS with 79.85 per cent. of copper will be formed. (If a current of carbonic acid is used, too much Cu,S is obtained, in consequence of the less complete decomposition of the cupric sulphide.) Of nickel coins, 0.5 grammes (7.71 grains) are dissolved in nitric acid and evaporated to dryness with 1 cubic centimeter (0.06 cubic inch) of sulphuric acid, the residue is dissolved in 200 cubic centimeters (12.2 cubic inches) of boiling water, and the solution precipitated with sulphuretted hydrogen, etc. Apparatus' for igniting in a current of hydrogen (Fig. 52).—a, a vessel with water and zinc; b, funnel for pouring in sulphuric acid; c, discharge pipe for the gas; d, drying tube of calcium chloride; e, gas discharge-pipe; g, porcelain crucible with perforated cover (Rose's 1 Sicherheitsvorrichtung für Wasserstoffentwicklungsapparate in Fresenius' Zeitschr. xvi. 93. Poggendorf's Ann. 1876, Heft. 10. crucible); 7, lamp. Fig. 53-a, gas generating flask with funnel tube b; c, wash vessel with concentrated sulphuric acid; d, calcium chlo Fig. 52. α ride tube; e, bulb-tube for the reception of the substance. It is advisable to pass the gas first through a solution of potassium permanganate, Fig. 53. and next, a solution of sodium hydrate to free the hydrogen from hydrocarbons, etc. 4. Assay with sulphocyanide.'-This method allows of the presence of nickel, zinc, iron, and arsenic; 0.5 to 1 gramme (7.71 to 15.43 grains), or more, of the assay sample is dissolved in nitric acid and evaporated to dryness with sulphuric acid until the free sulphuric acid is completely expelled. The dry mass is now dissolved with a little water and Fresenius' Ztschr. xvii. 55. tion. a large quantity of sulphurous acid added to the cold soluPotassium sulphocyanide is then gradually added until white copper sub-sulphocyanide is precipitated (if too much potassium sulphocyanide is added at one time, the black sulphocyanide is formed which is only gradually reduced to sub-sulphocyanide by sulphurous acid.) A sufficient quantity of the sulphocyanide salt has been added when the fluid commences to assume a reddishbrown color. This coloration is caused by the presence of iron, but the fluid will, in a short time, become entirely colorless. The precipitate is allowed to settle and is then decanted with cold water until a solution of silver nitrate is not rendered turbid by the wash water. It is then filtered upon a previously weighed filter and dried for 12 hours at 105° to 110° C. (221° to 230° F.), and weighed (100 Cu¿SCу2 52.2 Cu). In order to control the correctness of the result, the filter is incinerated by itself, the copper sulphocyanide is heated in a porcelain crucible to decompose the sulphocyanide, and is then ignited with sulphur in a current of hydrogen, and treated as on page 121. Nickel coins.-1 gramme (15.43 grains) is dissolved in 10 cubic centimeters (0.61 cubic inch) of nitric acid of 1.18 specific gravity, and evaporated to dryness with 1 cubic centimeter (0.061 cubic inch) of concentrated sulphuric acid. The dry mass is dissolved in a little water, and to the solution is added 50 cubic centimeters (3.05 cubic inches) sulphurous acid solution, and 2 grammes (30.87 grains) of potassium sulphocyanide. After having stood for 12 hours it is filtered, etc. For the determination of nickel in the filtrate see "NICKEL." Copper alloyed with tin (bronze).-1 gramme (15.43 grains) of the alloy is dissolved in a mixture of 6 cubic centimeters (0.36 cubic inch) of concentrated nitric acid of 1.5 specific gravity with the addition of 3 cubic centimeters (0.18 cubic inches) of water. When the action of the acid has ceased the contents of the dish is heated for a time, and next treated with 40 cubic centimeters (2.44 cubic inches) |