Zinc oxide

“ 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. ”

“ The heat evolved reduces the ore and distills the zinc, and the zinc fumes are condensed in the condensing chamber, precisely as in the present method of zinc making, with this important exception that, aside from the reaction produced by heating carbon in the presence of zinc oxide, the electric current, in passing through the zinc oxide, has a decomposing and disintegrating action upon it, not unlike the effect produced by an electric current in a solution. This action accelerates the reduction, and promotes economy in the process. ”

“ Carbonates, silicates and oxides of zinc are found. Crude zinc (spelter) is distilled from roasted ore.
Brass, German silver and other alloys contain zinc. Galvanized iron consists of a coating of zinc on sheet iron. Zinc oxide (zinc white) resembles white lead and is used in paints.
Used in electric batteries, making hydrogen, zinc etchings, etc. The greatest amount of zinc is used in alloys and zinc compounds. Zinc and zinc ores are both imported and exported by the United States, the imports exceeding the exports. Zinc oxide is exported in larger amount than any other form. ”

“ 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. ”

“ The roasting is carried on in order to obtain an oxide instead of a sulphur compound, the oxide being reducible by charcoal. These methods, introduced ages ago, are met with in nearly all metallurgical works for practically all ores. For this reason the preparatory treatment of zinc blende furnishes zinc oxide: this is already contained in calamine.
[7 bis] with very impure ores, especially such as contain lead (PbS often accompanies zinc) , the vapour of the reduced zinc is allowed to pass directly into the air. It burns and gives ZnO, which is used as a pigment. ”

“ Although zinc white is a most important pigment, it is very seldom made in colour works, because on account of its origin it is a product of metallurgical processes. Zinc white in chemical composition is pure zinc oxide; it is formed when zinc vapour burns in air. In zinc-smelting works zinc white is obtained by putting zinc in tubes which are heated to whiteness; the zinc vapours burn when they come in contact with the air, and the zinc oxide is caught by special arrangements.
The retorts used for this purpose are similar to those employed in the manufacture of coal gas. ”

“ 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. ”

“ The reduction of metallic zinc from its ores is based on the fact that zinc oxide [7] is easily reduced by charcoal at a red heat: ZnO + C [43] = Zn + CO. The zinc thus obtained is in a finely divided state and impure, being mixed with other metals reduced with it, but the greater portion is converted into vapour, from which it easily passes into a liquid or solid state. The reduction and distillation are carried on in earthenware retorts, filled with a mixture of the divided ore and charcoal. ”

“ The magnetic concentrates contain enough zinc to be well adapted to the manufacture of zinc oxide. Magnetic concentration is also applied in the removal of an excess of iron from partially roasted blende. Neither mechanical non-magnetic concentration can effect much in the way of separation when, as in many complex ores, carbonates of iron, calcium and magnesium replace the isomorphous zinc carbonate, when some iron sulphide containing less sulphur than pyrites replaces zinc sulphide, and when gold and silver are contained in the zinc ore itself. ”

“ 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. ”

“ Freytag (1868) carried out various experiments on the influence of zinc oxide and its compounds on vegetation, and found that all plants are capable of absorbing zinc oxide by their roots when grown on soils containing such oxide. Generally speaking the zinc is deposited chiefly in the leaves and stems, very little being found in the seeds, such minute traces occurring that he stated that the seeds must be harmless for men and animals. The general content of ZnO in plants is given as ·5–1·0% of ash, except in the abnormal case of plants growing on calamine. ”

“ A basic zinc yellow prepared from the sodium salt has a redder and more cloudy shade than one made from the potassium compound, but the difference is hardly noticeable when sodium-potassium chromate is employed.
Modern zinc yellows are invariably prepared from acid solutions, and consist of a double salt of zinc chromate and potassium bichromate, mixed with a varying amount of unchanged zinc oxide, which must not be regarded as an adulteration of the pigment, for its presence gives the substance “body.” ”

“ Zinc oxide, ZnO, is a white powder, almost insoluble [40] in water, [2] like magnesia, from which, however, it is distinguished by its solubility in solutions of sodium and potassium hydroxides. [3] Zinc chloride [4] is decomposed by water, combines with ammonium [41] chloride, potassium chloride, &c., just like magnesium chloride, forms an oxychloride, and also combines with zinc oxide. [4 bis]
Zinc, like many heavy metals, is often found in nature in combination [42] with sulphur, forming the so-called zinc blende, [5] ZnS. It sometimes occurs in large masses, often crystallised in cubes ”

“ 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. ”

“ In quantity of oil required the substitutes named compare well with white lead, some taking a little more and some a little less, except oxide of zinc, which takes a very large quantity. In the matter of susceptibility to impure air, they all have a distinct advantage over white lead. Zinc oxide is not at all affected, and the sulphate is very slightly affected unless the gas is in very large quantities and the paint is wet. In durability under outdoor exposure they are not better than white lead, except that oxide of zinc remains white. ”

“ The ordinary house-painter, therefore, accustomed to the use of lead paint, cannot expect to obtain the same result from zinc paint treated in the same way. And zinc oxides differ in value as pigments according to the methods of production. That obtained by direct roasting of the ore (franklinite and zincite) is superior to that prepared by the indirect method of oxidation of spelter.
Zinc sulphide enters into the composition of many white paints mixed with zinc oxide, barytes, and often lead sulphate. ”

“ If a plate of clean bright zinc is placed in a vessel containing some dilute sulphuric acid, energetic action occurs from the oxidation of the metal, and its union as an oxide with the acid, and the escape of a multitude of bubbles of hydrogen gas. After the action has proceeded some time, the zinc may be removed, and if a little quicksilver is now rubbed over the surface with a woollen rag tied on the end of a stick, it unites with the metal, and the surface of the zinc assumes a brilliant silvery appearance, and is said to be amalgamated. ”

“ 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. ”

“ The working range is 0.25 to 10 mg/m 3 for a 200-L air sample. The method does not distinguish zinc oxide fume from zinc oxide dust.
INTERFERENCES: Major interferences include Fe 2O 3, Zn, Zn (NH 3) 2Cl2, (NH 4) 3ZnCl 5, (NH 4) 2ZnCl 4 and (NH 4) 2Zn (SO 4) 2 6H 2O; these are resolved by using alternate analyte peaks. Particle size affects intensity measurements.
OTHER METHODS: This method combines and replaces Methods P&CAM 222 [1] and S316 [5] . The criteria document contains an elemental analysis for zinc [6] . ”

“ Huebner’s Cement.—Zinc oxide, 500.0 parts; powdered manganese, 1.5 parts; yellow ocher, powdered, 1.5–4.0 parts; powdered borax, 10.0 parts; powdered glass, 100.0 parts.
As a binding liquid it is well to use acid-free zinc chloride, which can be prepared by dissolving pure zinc, free from iron, in concentrated, pure, hydrochloric acid, in such a manner that zinc is always in excess. When no more hydrogen is evolved the zinc in excess is still left in the solution for some time. The latter is filtered and boiled down to the consistency of syrup. ”

“ It has been of great importance in the synthesis of organic compounds, and is the type of a large series of similar compounds, as zinc ethyl, zinc amyle, etc. -- Zinc oxide (Chem.) , the oxide of zinc, ZnO, forming a light fluffy sublimate when zinc is burned; -- called also flowers of zinc, philosopher's wool, nihil album, etc. The impure oxide produced by burning the metal, roasting its ores, or in melting brass, is called also pompholyx, and tutty. -- Zinc spinel (Min.) , a mineral, related to spinel, consisting essentially of the oxides of zinc and aluminium; gahnite. ”

“ They are liable to explode if rubbed together in a mortar, on account of the presence of sulphur and chlorate of potash, and the composition, if kept for any time, is liable to take fire spontaneously.
Tenth Experiment.
Some zinc is melted in an iron ladle, and made quite red hot; if a little dry nitre is thrown upon the surface, and gently stirred into the metal, it takes fire with the production of an intense white light, whilst large quantities of white flakes ascend, and again descend when cold, being the oxide of zinc, and called by the alchemists the "Philosopher's Wool" (ZnO) . ”

“ Zinc chloride is used to prevent the oxidation. It fuses on being heated, and, covering the metal with an oily coating, prevents contact with the air; but even if any oxide has formed, the free hydrochloric acid generally existing in the zinc chloride solution dissolves it, and in this way the metallic surface of the metals to be soldered is preserved fit for the adhesion of the liquid solder, which, on cooling, binds the objects together. ”

“ 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. ”

“ Zinc is not found in a native state. This ore is in the form of an oxide, as it is called. In roasting, certain of the impurities are driven off in gases, and mixing it with charcoal or coke and then applying heat to the confined mass, causes the zinc to melt and finally go off into a gas, as we shall presently see. ”

“ It is generally recognized that the purest ores produce the purest metal. Grades of commercial zinc are usually based on selected ores, and brands, when they mean anything usually mean that the metal is made from certain ores. Chemical control of the metal purchased is not nearly as common as it should be, and the refining of zinc is at best an imperfect operation. To obtain the metal chemically pure a specially prepared pure oxide or salt of zinc is distilled. ”