Zinc sulfide

“ If the zinc is present as blende, this operation offers considerable difficulties, because in the roasting process the zinc sulphide passes in the first instance into sulphate, which demands a high temperature for its conversion into oxide. Another point to be considered in this connexion is that the masses of sulphur dioxide evolved, being destructive of vegetable life, are an intolerable nuisance to the neighbourhood in which the operations take place. ”

“ Pure zinc is not affected by dilute sulphuric acid, but it is too expensive to use in cells; so amalgamated zinc is used instead, because it is cheaper, and acts the same as pure zinc. The impurities are removed from the surface of the zinc, as the zinc alone is dissolved by the mercury. ”

“ These experiments, when taken together, show that sulphate of zinc, though a moderately active irritant, is more indebted for its activity to a remote operation on some vital organ.
Sulphate of zinc is absorbed in the course of its action; for Orfila has lately found it by his process for complex mixtures in the spleen, liver, and urine of animals. [1197]
The effects of the preparations of zinc on man in large doses have not been particularly studied. In the dose of a scruple or a drachm, the sulphate is the most immediate emetic known ”

“ Zinc dust contains both metals and their oxides, and methods which, from the volume of hydrogen generated, determine indirectly the percentage of metallic zinc do not give the real composition of the zinc dust. For the determination of the metallic components the material is digested with a solution of copper sulphate, which dissolves zinc and cadmium; the liquid is filtered, acidified, and decomposed with hydrogen sulphide, or treated with a solution of ammonium carbonate. ”

“ Zinc is detected by dissolving the substance in hydrochloric or nitric acid, boiling, and adding sodic hydrate in excess, filtering, and adding ammonic sulphide to the filtrate. The precipitate contains the zinc, which can be dissolved out by boiling with dilute sulphuric acid, and detected by the formation of a white precipitate on the addition of potassic ferrocyanide.
The dry assay of zinc can only be made indirectly, and is unsatisfactory. Zinc is volatile, and at the temperature of its reduction is a gas. ”

“ Zinc itself is readily soluble in dilute acids; any residue which is left after boiling with dilute hydrochloric or sulphuric acid consists simply of the impurities of the metal; this is generally lead.
All zinc compounds are either soluble in, or are decomposed by, boiling with acids, the zinc going into solution. Zinc forms only one series of salts, and these are colourless. Their chief characteristic is solubility in an alkaline solution, from which sulphuretted hydrogen produces a white precipitate of zinc sulphide. ”

“ The only certain method of detection is to produce the sulphide of zinc, best effected by saturating a neutral or feebly acid liquid with hydric sulphide. If an organic liquid, which can be easily filtered, is operated upon, it may be strongly acidulated with acetic acid, and at once treated with hydric sulphide. If, however, zinc is sought for as a part of a systematic examination (as will most likely be the case) , the solution will have been treated with hydrochloric acid, and already tested for arsenic, antimony, lead, &c., and filtered from any precipitate. ”

“ In this respect the action of zinc varies a great deal with the degree of its purity. Weak sulphuric acid (corresponding with the composition H2SO4,8H2O) at the ordinary temperature does not act at all on chemically pure zinc, and even a stronger solution acts very slowly. If the temperature be raised, and particularly if the zinc be previously slightly heated, so as to cover the surface with a film of oxide, chemically pure zinc acts on sulphuric acid. ”

“ Zinc ores, in the several varieties of carbonates, silicates, oxide, sulphide and sulphate of zinc, have been found in several of the Australian states but have attracted little attention except in New South Wales, where special efforts are being made successfully to produce a high-grade zinc concentrate from the sulphide ores. ”

“ Zinc, free from other metals, may be obtained by distilling a mixture of charcoal and its subcarbonate, precipitated from the crystallized sulphate by carbonate of soda. By holding a porcelain saucer over the flame of hydrogen produced from the action of dilute sulphuric acid upon any sample of the zinc of commerce, the presence of arsenic in it may be made manifest by the deposit of a gray film of the latter metal. Antimony, however, produces a somewhat similar effect to arsenic. ”

“ With Zinc.—Add about 10 grams of granulated zinc; if the hydrogen comes off violently add water; if, on the other hand, the action is very slow, add sufficient dilute sulphuric acid to keep up a brisk effervescence. The reduction is hastened by warming, and is complete when the solution is quite colourless and a drop of the liquid tested with sulphocyanate of potassium gives no reaction for ferric iron. Filter through "glass wool" or quick filtering paper. The zinc should be still giving off gas rapidly, indicating a freely acid solution; if not, acid must be added. ”

“ A rod of perfectly pure zinc, when immersed in dilute sulphuric acid, is so very slowly attacked that there is no visible evolution of gas; but, if a piece of platinum, copper or other more electro-positive metal be brought into contact with the zinc, it dissolves readily, with evolution of hydrogen and formation of the sulphate. The ordinary impure metal dissolves at once, the more readily the less pure it is. Cold dilute nitric acid dissolves zinc as nitrate, with evolution of nitrous oxide. ”

“ The theory is that zinc, though subject to oxidization, has the peculiarity that the oxide does not scale off as from iron, but forms a permanent coating impervious to the action of the atmosphere. Some mechanics, however, assert that neither zinc, copper, nor lead will withstand the action of our atmosphere, as bituminous coal strongly impregnated with sulphur is almost the only fuel used. It is claimed by some that the sulphurous acid in the atmosphere tends to corrode zinc so as to make it worthless for roofs or gutter linings. ”

“ Plates of platinum and pure or amalgamated zinc are separated by a porous pot, and each surrounded by some of the same solution of a salt of a metal more oxidizable than zinc, such as potassium. When the plates are connected together by means of a wire, no current flows, and no appreciable amount of zinc dissolves, for the dissolution of zinc would involve the separation of potassium and a gain in available energy. If sulphuric acid be added to the vessel containing the zinc, these conditions are unaltered and still no zinc is dissolved. ”

“ To the colour of oxide of zinc, sulphuretted hydrogen is altogether harmless; sulphide of zinc being itself white. The variety under notice [76] works and washes well, possesses no pasty or clogging properties, and is prepared beautifully white. Moreover, it has the desirable quality of dense body; so much so, that, as the painter works, his effects remain unaltered by the drying of the colour. It may likewise be safely mixed with all other pigments, the following blending very satisfactorily with the white for opaque lights—cadmium yellow, orange, and red ”

“ Zinc (Zn) .—This metal is found in considerable abundance, but never occurs in the pure metallic state, but in combination with other substances, chiefly as sulphide in zinc blende, as carbonate in calamine, and as the silicate in the kieselzinc ore; also, with sulphuric acid, the "vitriol of zinc."
Zinc is of a bluish-white color and metallic lustre, is crystalline and brittle when heated 400°F., but malleable and ductile between 200° and 300°. It will not oxidize in dry air, but tarnishes if exposed to air containing moisture, first becomes grey, and then passes into the white carbonate. ”

“ At a red heat, zinc inflames, and the product of combustion is the white oxide of zinc, or flowers. The oxide of zinc is reduced by mixing it with charcoal, and exposing the mixture to a strong heat in close vessels.
Zinc will burn in chlorine gas, and forms a chloride of zinc. If the perchloride of mercury and zinc-filings be heated together, the same compound will result. This chloride melts at 212°, and rises, in the gaseous form, at a heat much below ignition. It was formerly called the butter of zinc, and muriate of zinc. With iodine, zinc forms a compound, called iodide of zinc. ”

“ Preparation of pure Oxide of Zinc, by M. Hermann.—It is by no means easy to obtain this substance perfectly pure; the following is M. Hermann’s process: Oxide of zinc, or metallic zinc, is to be dissolved in excess of sulphuric acid, and the solution being filtered, sulphuretted hydrogen is to be passed through, so long as a brown or yellow precipitate is formed. Cadmium, lead, or copper, being thus separated, and the solution filtered, it is to be treated with solution of the chloride of lime, (bleaching powder,) by which the iron and manganese will be separated. ”

“ These impurities are determined by well-known methods; sulphur is oxidized and precipitated with barium chloride, lead by sulphuric acid and alcohol. The examination of zinc dust, when used for the regeneration of metal, determines the quantity of zinc resident therein, and employed as reducing agent, the quantity of metal which causes the generation of hydrogen. Cadmium, showing the same deportment, must also be considered as well as lead and arsenic. ”

“ If the zinc oxide dissolves with effervescence, white lead or whiting may be present; the solution should give no precipitate of black sulphide of lead on passing sulphuretted hydrogen through it. On neutralising the solution in nitric acid with sufficient ammonia, and adding ammonia sulphide to precipitate all the zinc (the precipitate should be white, any other colour would show some impurity) , filtering off and adding a little oxalate of ammonia, no white precipitate of calcium oxalate should be obtained; such a precipitate would show presence of whiting or gypsum. ”

“ The advantages of the zinc method are, that it is easily worked and that the excess of zinc is readily removed by simply filtering. The disadvantages are the slowness [68] with which the last portions of ferric iron are reduced, the danger of loss by effervescence, the precipitation of basic salts, and, perhaps, of iron, and the loading of the solution with salts of zinc, which in the titration with bichromate have a prejudicial effect. ”

“ The various modifications of zinciferous flue ashes from blast furnaces are an object for continual demand, being both a valuable material for the production of zinc and, in its superior qualities, a desirable pigment. In the regeneration of zinc the presence of foreign substances is of some concern; detrimental are lead, sulphur, and sulphuric acid in form of lead, zinc, and lime sulphate. ”

“ No zinc is used, only care in washing out, drying out, and managing the water." This is the evidence of an engineer with a large number of vessels in his charge. On the other hand, some of the most prominent Liverpool engineers always use zinc, and take care to apply it most strictly. The evidence of one of them is as follows: "We always fix slabs of zinc to most boilers, exposing not less than a surface of one square foot for every twenty indicated horse-power, and distributed throughout the boiler. This zinc we find to be in a state of oxide and crumbling away in about three months. ”

“ Of these, zinc dust is the only ready product which is, as color or reducing agent, employed in analytical and technical processes. Its value, when serving the latter purpose, is determined by the percentage of finely divided metallic zinc and cadmium contained therein; of equal reducing power is cadmium, generally associating zinc; injurious, and therefore uneffective, are zinc oxide and oxides of other metals, also metallic lead. ”

“ Suitable proportions are:—Zinc oxide, 100 parts; sulphuric acid (66° B.) 60; and potassium bichromate, 100. Although it is hardly possible that any hydration takes place, it is found advisable to soak the zinc oxide in water for 24 hours before [270] the other reagents are added, the sulphuric acid after dilution being added gradually. Great care must be taken that the solutions are all cold, and the stirring is continuous, to avoid the pigment being deposited in a hard sandy form. Zinc yellows thus prepared are not liable to change during washing in a manner analogous to the lead compounds. ”

“ As it is not easy to obtain zinc perfectly free from admixture of other metals, an artifice is commonly resorted to for obtaining a surface of pure metal, by rubbing a plate of the ordinary metal with quicksilver, which readily dissolves pure zinc, but is without action on the iron and other metals with which the zinc is contaminated, while the quicksilver is not acted upon by the diluted acid, but is merely the vehicle by which the pure zinc is presented to the liquid. ”

“ Calvert and Johnson made the following series of observations on the action of sulphuric acid of various degrees of concentration on 2 grams of pure zinc during two hours. In the cold the concentrated acid, H2SO4, does not act, H2SO4,2H2O dissolves about 0·002 gram, but principally forms hydrogen sulphide, which is obtained also when the dilution reaches H2SO4,7H2O, when 0·035 gram of zinc is dissolved. When largely diluted with water, pure hydrogen begins to be disengaged. H2SO4,2H2O at 130° gives a mixture of hydrogen sulphide and sulphurous anhydride dissolving 0·156 gram of zinc. ”