Chromite

“ The theoretical formula FeCr2O4 corresponds with chromic oxide (Cr2O3) 68%, and ferrous oxide 32%; the ferrous oxide is, however, usually partly replaced by magnesia, and the chromic oxide by alumina and ferric oxide, so that there may be a gradual passage to picotite or chromespinel. Much of the material mined as ore does not contain more than 40 to 50% of chromic oxide. In the form of isolated grains the mineral is a characteristic constituent of ultrabasic igneous rocks, namely the peridotites and the serpentines which have resulted from their alteration. ”

“ Chrōmatop′sia, coloured vision; Chrō′matrope, an arrangement in a magic-lantern by which effects like those of the kaleidoscope are produced; Chrō′matype, Chrō′motype, a photographic process by which a coloured impression of a picture is obtained.—adj. relating to the chromatype.—ns. Chrōme, Chrō′mium, a metal remarkable for the beautiful colours of its compounds.—adj. Chrōm′ic.—ns. Chrō′mite, a mineral consisting of oxide of chromium and iron; Chrō′mo-lith′ograph, or merely Chrō′mo, a lithograph printed in colours ”

“ CROCOITE, a mineral consisting of lead chromate, PbCrO4, and crystallizing in the monoclinic system. It is sometimes used as a paint, being identical in composition with the artificial product chrome-yellow; it is the only chromate of any importance found in nature. ”

“ I say life, for I take it that this company admits that a slab of granite is as much alive as any man or woman I see before me. But I have manufactured gold, and I could have manufactured protoplasm if I had devoted my life to that object. My studies have been almost wholly on the inorganic plane. Hence the 'philosopher's stone' came in my way, but not the 'elixir of life.' The molecules of protoplasm are only a little more complex than the molecules of hydrogen or nitrogen or iron or coal. ”

“ Chrō′mosphere, a layer of incandescent red gas surrounding the sun through which the light of the photosphere passes—also Chrōmat′osphere; Chrō′mo-typog′raphy, typography in colours; Chrō′mo-xy′lograph, a picture printed in colours from wooden blocks; Chrō′mo-xylog′raphy.—Chromatic scale, a scale proceeding by semitones; Chromic acid, an acid of chromium, of an orange-red colour, much used in dyeing and bleaching. [Gr. chrōmatikos—chrōma, colour.]
Chronic, -al, kron′ik, -al, adj. lasting a long time: of a disease, deep seated or long continued, as opposed to acute.—n. ”

“ There are crystals as big as cathedral pillars, delicate as mildew and sharp as needles; plain, blue, green like nothing in the world, of fiery colours or black; mathematical, perfect, like the contrivances of queer and bewildered sages; or recalling livers, hearts, gigantic human organs and animal fluids. There are crystalline caves or spectral bubbles or mineral dough; there is mineral fermenting, grilling, growth, architecture and engineering; I vow that a Gothic church is not the most complicated of crystals. Even within us there persists a crystalline power ”

“ A dark green pigment prepared from oxide of chromium; mixed with Prussian blue and chrome yellow it is called Green Cinnabar.
Chrome Ochre. Oxide of chromium of a fine yellowish green.
Chrome Red. A chromate of lead; a durable pigment used in oil painting. (See Red Lead.)
Chrome Yellow. A chromate of lead, which makes a bad pigment for oil painting. It is very poisonous and not durable; when mixed with white lead it turns to a dirty grey. As a water-colour pigment it is less objectionable. ”

“ Precious stones so formed would be colorless if, in the terrible furnace of the primordial world, fire-proof metals had not taken upon themselves the task performed by aniline in our present dying-works. Long before there were colored plants and animals, metals played the part of pigments in Nature, and thus produced, in stones, colors almost surpassing in brilliancy those to be found in the animal kingdom. Rubies and emeralds are probably colored with chrome, sapphires with cobalt, lapis-lazulis with iron, and other precious stones with copper, nickel, manganese, etc. ”

“ Cool, and weigh. The substance is chromic oxide, Cr2O3, and contains 68.62 per cent. of chromium. It is a dark-green powder insoluble in acids.
When, as is generally the case, the chromium exists altogether as chromate (phosphates and arsenates being absent) it is best to proceed as follows:—Render the solution acid with acetic acid, then add sodium acetate to the solution and heat nearly to boiling; next treat with a slight excess of acetate of lead, and boil. Allow to settle, and filter. Wash the precipitate with hot water, dry in the water-oven or at a low temperature. ”

“ Oxyhalogen derivatives of chromium are known, the oxychloride, CrO2Cl2, resulting on heating potassium bichromate and common salt with concentrated sulphuric acid. It distils over as a dark red liquid of boiling point 117° C., and is to be regarded as the acid chloride corresponding to chromic acid, CrO2 (OH) 2. It dissolves iodine and absorbs chlorine, and is decomposed by water with formation of chromic and hydrochloric acids; it takes fire in contact with sulphur, ammonia, alcohol, &c., and explodes in contact with phosphorus; it also acts as a powerful oxidizing agent. ”

“ The oxygen and nitric acid remain unaltered [53] in quantity or quality during these changes, being merely transferred from one metal to another.
A piece of zinc will displace the iron in like manner, leaving a solution of nitrate of zinc.
Nearly all the colors used in the arts are produced by metals and their combinations; indeed, one is named chromium, from a Greek word signifying color, on account of the beautiful tints obtained from its various combinations with oxygen and the other metals. All the various tints of green, orange, yellow, and red, are obtained from this metal. ”

“ The very name leads one to expect something different to the other metals—chroma, colour. The metal is procured from what is known as chrome-ironstone, a combination of protoxide of iron and sesqui-oxide of chromium (FeOCr2O3) . By ignition with potassium we get chromic acid and chromate of potassium, a yellow salt which is used to make the other compounds of chromium. The metal is by no means easy to fuse. ”

“ Just as the real nature of a person is first disclosed by his behavior under trying circumstances, so of a crystal it is its conduct under stress of one sort or another which brings out its real character. By way of illustration let us prepare a sphere from the mineral quartz—it matters not whether we destroy the beautiful outlines of the crystal or employ a battered fragment—and then prepare a sphere of similar size and shape from a noncrystalline or amorphous substance like glass. ”

“ From a black and amorphous matter we have made to issue crystalline substances of every shade of color—reds, saffrons, greens, violets, and blues—alizarine, the same substance as tints the flowers of the madder, and that wonderful aniline, colorless as the ray of light before it has been resolved by the prism, but containing in posse, like the same ray, all the colors of the rainbow. What do we know of stone-coal, the origin of so many marvels and refractory to all analysis? ”

“ One sees at first crystal skeletons, then gradually the crystals developing into perfection. Neither the chemist with all his delicate tests, nor the physician armed with his accurate instruments can decipher the feeblest trace of heterogeneity; the child grown has become a man; the mineral fully developed has reached also its age of virility.
Minerals may be hindered in their development, may become irregular, imperfect, deformed; upon certain of their angles new facets may appear, in other parts facets may slowly become obliterated. ”

“ In shape, crystallisation, fracture and hardness, it is the same, and often contains, in addition to the chromium, the further addition of traces of carbonate of lime, magnesia, and occasionally faint traces of hornblende and mica, which evidently result from its intimate association with the granite rock and gneiss, amongst which it is mostly found, the latter rocks being of a slaty nature, in layers or plates, and, like granite, containing mica, pyrites, felspar, quartz, etc. ”

“ CRYSTAL CAPRICE
Formal Lecture in Schoolroom, after some practical examination of minerals.
L. We have seen enough, children, though very little of what might be seen if we had more time, of mineral structures produced by visible opposition, or contest among elements; structures of which the variety, however great, need not surprise us: for we quarrel, ourselves, for many and slight causes,--much more, one should think, may crystals, who can only feel the antagonism, not argue about it. ”

“ Chrome yellows are chromates of lead, produced by mixing dilute solutions of acetate or nitrate of lead and bichromate of potash. This makes a medium tint known as middle chrome. The addition of sulphate of lead makes this paler, when it is known as lemon chrome, whereas the addition of caustic lime makes an orange chrome of a darker color. The chromes mix well with oil and with white lead either in oil or water. They stand the sun well, but like other lead salts, become dark in bad air. ”

“ Christophany, kris-tof′a-ni, n. an appearance of Christ to men. [Gr. Christos, and phainein, to appear.]
Chromatic, krō-mat′ik, adj. relating to colours: coloured: (mus.) relating to notes in a melodic progression, which are raised or lowered by accidentals, without changing the key of the passage, and also to chords in which such notes occur.—ns. Chrōm′ate, a salt of chromic acid; Chrōmat′ics, the science of colours.—v.t. Chrō′matise, to impregnate with a chromate.—ns. Chrōmatog′raphy, a treatise on colours; Chrōmatol′ogy, the science of colours, or a treatise thereon ”

“ Chroma is the strength of a color. It is the quality by which we distinguish a strong color from a weak one. The standard hue is approximately full chromatic intensity. Likewise each tint and shade is considered to be of its full chromatic intensity, making the left-hand boundary of the rectangle the area of full chroma. ”

“ No more correct estimates of the comparison of crystal individualities would be obtained by the study of outward forms alone of two minerals than would be gained by a judgment of persons from the cut of their clothing. Too often this outward dress tells only of the conditions by which both men and crystals have been surrounded, and but little of the power inherent in the individual. Many a battered mineral fragment with little beauty to recommend it, when placed under suitable conditions for its development, has grown into a marvel of beauty. ”

“ It will be remembered that the chroma of the sphere ceased with 5 at the equator. The color tree prolongs 24 this through 6, 7, 8, and 9. The branch ends carry colored balls, representing the most powerful red, yellow, green, blue, and purple pigments which we now possess, and could be lengthened, should stronger chromas be discovered.12
(35) Such models set up a permanent image of color relations. Every point is self-described by its place in the united scales of hue, value, and chroma. These scales fix each new perception of color in the child’s mind by its situation in the color solid. ”

“ In the inorganic world, where the great phenomena of life are wanting, we have constantly exhibited the working of powers of a strangely complicated kind. The symmetrical arrangement of crystals—the diversified characters of mineral formations—the systematic aggregations of particles to form masses possessing properties of a peculiar and striking nature—all prove, that agencies, which science, with all its refinements, has not yet detected, are unceasingly at work. ”

“ The test for a chrome is tinting strength, taking care to make a comparison with the same grade of colours, that is, light, medium or orange chrome. Fineness is another important test. Placing a small quantity on glass and passing a palette knife over it and pressing firmly will detect grit if present. In the lighter chromes it is well to look for the greyness of tone which is objectionable. Chromes mix well with white lead and are strong in body.
Ochres. —Analysis is of no value in determining the value of an ochre. Sometimes chrome yellow is used to tone it up. ”

“ Science describes chroma as the purity of one wave length separated from all others. Other wave lengths, INTERMINGLING, make its chroma less pure. A beam of daylight can combine all wave lengths in such balance as to give the sensation of whiteness, because no single wave is in excess.8
(24) The color sphere (see Fig. 1) is a convenient model to illustrate these three qualities,—hue, value, and chroma,—and unite them by measured scales.
(25) The north pole of the color sphere is white, and the south pole black. Value or luminosity of colors ranges between these two extremes. ”

“ No crucible yet constructed can hold a native sapphire, and all the alchemy of man directed to this point has failed to extort from carbon the secret of its diamond—the little crystal that earth with all her chemistry has made so few of, since first heat and water, Nature's gem-smiths, joined their forces to produce the glittering stones. ”

“ The oxide thus obtained is used as a green pigment for china and enamel. The anhydrous chromic oxide obtained from chromyl chloride, CrO2Cl2, has a specific gravity of 5·21, and forms almost black crystals, which give a green powder. They are hard enough to scratch glass, and have a metallic lustre. The crystalline form of chromic oxide is identical with that of the oxide of iron and alumina, with which it is isomorphous.
[7 bis] The most important of the compounds corresponding with chromic oxide is chromic chloride, Cr2Cl6, which is known in an anhydrous and in a hydrated form. ”