Cadmium

“ It has been found in this laboratory that perfectly pure cadmium or zinc can be prepared only by repeated distillations, each one being carried on slowly to allow the impurities to separate by means of their difference in volatility.
2 The supposed mixture of metal and oxide resulting from the decomposition of the oxalate was only moistened with a few drops of nitric acid in order to reoxidize any reduced metal. ”

“ The very low result as compared with all subsequent work was probably due to the presence of a small amount of zinc, since the cadmium used was obtained from zinc ores and no adequate means of separation from the zinc is described.
von Hauer, Journ. f. prakt. Chem. 72, 338. 1857. His method consisted in reducing a weighed amount of cadmium sulphate to the sulphide in a stream of hydrogen sulphide, under pressure, at an elevated temperature, and weighing the sulphide. The reduction was shown to be complete by proving the absence of sulphate in the sulphide. ”

“ Analysis: When the new substance is heated it fuses to a red liquid and then breaks up into metal and the chloride of cadmium. Its reactions are in general those of a strong reducing agent. Treated with nitric acid, oxides of nitrogen are liberated. ”

“ When distilled the cadmium volatilises sooner, because it has a lower boiling point. Sometimes the zinc dust obtained by the first distillation of zinc contains as much as 5 per cent. of cadmium. When zinc blende, containing cadmium, is roasted, the zinc passes into the state of oxide, and the cadmium sulphide in the ore oxidises into cadmium sulphate, CdSO4, which resists tolerably well the action of heat; therefore if roasted zinc blende be washed with water, a solution of cadmium sulphate will be obtained, from which it is very easy to prepare metallic cadmium. ”

“ It has in truth a lustrous luminosity not often to be met with, added to a total absence of rankness or harshness. A simple original colour, containing no base but cadmium, it is of perfect permanence, being uninjured by exposure to light, air or damp, by sulphuretted hydrogen, or by admixture. Having in common with cadmium sulphides a certain amount of transparency, it is invaluable for gorgeous sunsets and the like, either alone or compounded with aureolin. ”

“ Copper and cadmium consequently show the same group reactions in systematic analysis. The more intense colors of the copper compounds—the black sulphide, the intensely blue cupric-ammonium-ion—mask the cadmium reactions. But cupric-ion may be converted, by potassium cyanide, into a complex ion of extreme stability, from the solutions of which hydrogen sulphide and alkali sulphides fail to precipitate any sulphide of copper, while cadmium sulphide may be precipitated from the solutions of the much less stable complex cadmicyanide-ion. ”

“ In a short time the cadmium is precipitated, and attaches itself to the sides of the capsule, when it is collected, washed, and dried.
3. (Herapath.) When zinc is obtained by distilling its ores, per descensum, the first portion of the metallic fumes evolved burn with a brownish flame, and deposit oxide of cadmium, which is subsequently reduced by distillation with charcoal. Thousands of pounds of cadmium are yearly wasted at the zinc works which might be easily collected in a similar manner.
Prop., &c. Resembles tin in most of its physical properties, being white, soft, and malleable. Sp. gr. ”

“ From crude cadmium or its oxide, and hydrochloric acid, as last.
Cadmium, I′odide of. CdI2. Syn. Hydri′odate of cadmium; Cad′′mii iodi′dum, C. hydrio′das, L.
Prep. (Crookes.) Cadmium in filings 1 part, pure iodine 2 parts, are to be placed together in a capacious flask, with alcohol sufficient to cover them. Action commences at once, attended with considerable evolution of heat; when it ceases, heat the mixture till it is colourless; then filter from a few grains of cadmium which will remain undissolved, evaporate and crystallise. ”

“ The crystallizing power of the cadmium however, seems to be less, so that the only crystals suitable for measurement were extremely minute. The largest individuals were barrel-shaped, like those of zinc and resembled little piles of basal plates. Their side planes are not infrequently uneven and bent, probably as the result of the softness and great ductility of the metal.
Only the most minute crystals show pyramidal planes of comparative perfection. ”

“ Unless the entire mass of metal and oxide was dissolved there would be danger of the presence of free undissolved metal which would possess an appreciable vapor-tension below the temperature of decomposition of cadmium nitrate. An appreciable loss in weight resulting from a distillation of the metal out of the crucible might easily result. ”

“ The temperature of the water must not exceed 50°C. In water whose temperature approaches the boiling point the hydroxide is slowly decomposed with liberation of metal.
The new hydroxide is a strong reducing agent. It dissolves in dilute acids; yielding with nitric acid oxides of nitrogen, with hydrochloric or sulphuric acid free hydrogen. After washing with warm water until all the chlorine had disappeared, it was dried over phosphorus pentoxide and analyzed. [Pg 92]
First determination of cadmium. Second determination of cadmium. ”

“ Owing to the high specific gravity of the iodine compound some difficulty was experienced in obtaining a preparation [Pg 83] free from metal. This difficulty was finally overcome by keeping the material just above its melting temperature for a long time and constantly jarring the flask. During the process of cooling a decidedly greenish tint was observed which disappeared as the process was continued. When cold the substance resembled the chloride and bromide. Two determinations of cadmium were made in the first preparation. ”

“ Chromate of potash causes no precipitate in them, unless zinc or lead be present.
There is only one oxide of cadmium, the brown above-mentioned. Its specific gravity is 8·183. It is neither fusible nor volatile at a very high temperature. When in the state of a hydrate it is white. The oxide of cadmium consists of 87·45 parts of metal, and 12·55 oxygen in 100 parts. Berzelius states its atomic weight to be 55·833 to hydrogen 1·000. Its sulphuret has a fine orange yellow colour, and would form a beautiful pigment, could the metal be found in sufficient quantity for the purposes of art. ”

“ Provided the metal be freed from iron, which we have commonly found to be more or less present, a white of considerable beauty may be produced; either directly by precipitation as hydrated oxide or carbonate, or indirectly by exposing the brown anhydrous oxide to air and light—the latter mode yielding a product of greater opacity. However prepared, cadmium white is deficient in body, and apt to assume a yellow tint on meeting with an impure atmosphere. ”

“ Cadmium oxide is soluble, although sparingly, in alkalis, but in the presence of tartaric and certain other acids the alkaline solution of cadmium oxide does not change when boiled, whilst a diluted solution in that case deposits cadmium oxide: this may also serve for separating zinc compounds from those of cadmium. Cadmium is precipitated from its salts by zinc, which fact may also be taken advantage of for separating cadmium; for this reason, in an alloy of zinc and cadmium, acids first of all extract the zinc. Cadmium is in all respects less energetic than zinc. ”

“ It is used as a pigment (cadmium yellow) , for it retains its colour in an atmosphere containing sulphuretted hydrogen; it melts at a white heat, and on cooling solidifies to a lemon-yellow micaceous mass.
Normal cadmium carbonates are unknown, a white precipitate of variable composition being obtained on the addition of solutions of the alkaline carbonates to soluble cadmium salts.
Cadmium nitrate, Cd (NO3) 2·4H2O, is a deliquescent salt, which may be obtained by dissolving either the metal, or its oxide or carbonate in dilute nitric acid. It crystallizes in needles and is soluble in alcohol. ”

“ The method consists in taking a weighed amount of cadmium oxalate, decomposing it by heat, when a mixture of oxide and metal are said to be formed, dissolving this mixture in nitric acid, converting the nitrate into oxide and weighing the oxide. ”

“ Very pale cadmium yellows are not permanent, and lemon cadmiums are decidedly fugitive. Being, like the deep and 'pale' varieties, sulphides, they are of course unaltered by sulphurous gas; but they will not stand exposure to light and air, or even to light alone. ”

“ The method of work was to prepare pure metallic cadmium, to convert a weighed portion of the metal into nitrate by means of pure nitric acid, to decompose the nitrate completely to oxide and to weigh the oxide. ”

“ Carbonate of cadmium was 102made by dissolving pure cadmium in nitric acid, adding an excess of ammonia and a small quantity of ammonium carbonate. After standing for some time the cadmium carbonate was filtered off and rejected. The filtrate was treated with an excess of ammonium carbonate and the precipitated cadmium carbonate allowed to digest in it for some time. After washing by decantation several times the carbonate was transferred to a funnel containing a porcelain filter-plate, covered with a piece of ashless filter paper of slightly larger diameter, and washed thoroughly. ”

“ It seemed to do no harm, but in the fourth determination an effort was made to avoid 28it by using a porcelain tube instead of a glass combustion tube for heating to redness in a current of hydrogen sulphide.
The fact that sulphide of cadmium was always too light after the first hour’s heating in hydrogen sulphide proves that it must have contained some oxide of cadmium even after this heating. Oxide of cadmium is readily absorbed by the glaze on porcelain, and some error must have been introduced in this way because it would not be converted into sulphide after forming a silicate. ”

“ The average value found in the first five determinations = 111.910, in the last four = 111.977. The close agreement between the results obtained from the different preparations of the sulphate argues in favor of a fair degree of purity for all the material.
The method of weighing the more or less hygroscopic cadmium sulphate is open to criticism when employed in accurate work. The cadmium sulphate was placed in an open boat, dried, cooled over sulphuric acid, and weighed. ”

“ Cadmium is a white metal, possessing a bluish tinge, and is capable of taking a high polish; on breaking, it shows a distinct fibrous fracture. By sublimation in a current of hydrogen it can be crystallized in the form of regular octahedra; it is slightly harder than tin, but is softer than zinc, and like tin, emits a crackling sound when bent. It is malleable and can be rolled out into sheets. The specific gravity of the metal is 8.564, this value being slightly increased after hammering ”

“ The value assigned to cadmium varies from 111.48 to 112.32 on the basis of oxygen = 16. The best work has apparently been done by von Hauer, Lenssen and Huntington. The results of these three seem entitled to about equal confidence, yet the figure obtained by von Hauer differs from that of Huntington by three tenths of a unit. [Pg 3]
The more prominent difficulties which have been encountered were:
First. The preparation of cadmium compounds free from all impurities, and which at the same time were well adapted to weighing. ”

“ The black films of tin, lead and cadmium dissolve at once in the acid, the lead film being also soluble in bleaching-powder. The oxide films of antimony, arsenic, tin and bismuth are white, that of bismuth slightly yellowish; lead yields a very pale yellow film, and cadmium a brown one; mercury yields no oxide film. The oxide films (the metallic one in the case of mercury) are tested with hydriodic acid, and with ammonium sulphide, and from the changes produced the film can be determined (see F.M. Perkin, Qualitative Chemical Analysis, 1905) . ”

“ Several shades are obtained according as the solution of cadmium sulphate used in its precipitation is neutral or acid. The reason of this difference in shade lies apparently in the different size of the crystals of which the precipitate is composed. The deep, pure yellow colour becomes still deeper by fusion, which takes place at a white heat. Weak alkalis, acids and sulphuretted hydrogen do not alter cadmium yellow; it is thus to be regarded as a durable artists’ colour. It can be mixed with ultramarine without decomposition, when a fine green is formed ”

“ It is a fact of some interest in connection with the periodic arrangement of the elements, that the tendency toward the formation of a lower series of compounds which becomes so strongly developed in mercury begins to exhibit itself in some slight degree in cadmium. ”

“ The colour of the pure mineral is white; more often it is brownish, sometimes green or blue: a bright-yellow variety containing cadmium has been found in Arkansas, and is known locally as “turkey-fat ore.” The pure material contains 52% of zinc, but this is often partly replaced isomorphously by small amounts of iron and manganese, traces of calcium and magnesium, and sometimes by copper or cadmium.
Calamine is found in beds and veins in limestone rocks, and is often associated with galena and blende. ”

“ The silver chloride obtained always darkened on heating and contained cadmium, as was shown in the following manner: The lump of silver chloride was attached to the negative pole of a cell and electrolyzed in a bath containing dilute sulphuric acid. The resulting metal was then dissolved in nitric acid and the silver precipitated by adding hydrochloric acid. The filtrate was evaporated to expel the nitric acid and the residue taken up with water 65and tested for cadmium with hydrogen sulphide. An appreciable quantity was always found. ”