Ruby, redness

Aluminium oxide occurs naturally as emery (an impure form) and as corundum. Corundum is a crystalline form which may be coloured by traces of impurity, for example as ruby (red) and sapphire (blue). Small synthetic rubies and sapphires have been made by heating alumina with the colouring oxide in an oxy-hydrogen flame. 

Make a concentrated solution of anthracene in hot acetone. To about 2 ml. of this solution add a cold concentrated acetone solution of picric acid drop by drop, and note the formation of a red coloration which becomes deeper on further addition of the acid. If excess of picric acid is added, however, the solution becomes paler in colour, and this is to be avoided if possible. Boil to ensure that both components are in solution and then transfer to a small porcelain basin or watch-glass ruby-red crystals of anthracene picrate separate out on cooling. The product, however, is often contaminated with an excess of either anthracene or of picric acid, which appear as yellowish crystals. 

Bulka et al. (43) have demonstrated the electrophilic reactivity of selenazoles possessing an hydrazonc in the 2-position and nonsubstituted in the 5-position toward diazonium salt to give 5-phenylazo derivatives preferentially. For example, the main product of the coupling of 2-benzylidene hydrazino-4-phenylselenazole with diazo-o-phenetidine is the 5-(o-ethoxyphenylazo)-selenazole (Scheme 371 ruby red prisms, m.p. 206°C. yield 67"o). A formazan is obtained as by-product. (See Section III.6) (43). 

Ruby laser Ruby red glass Ruetschi vacancy model... 

Calcium carbonate has normal pH and inverse temperature solubilities. Hence, such deposits readily form as pH and water temperature rise. Copper carbonate can form beneath deposit accumulations, producing a friable bluish-white corrosion product (Fig. 4.17). Beneath the carbonate, sparkling, ruby-red cuprous oxide crystals will often be found on copper alloys (Fig. 4.18). The cuprous oxide is friable, as these crystals are small and do not readily cling to one another or other surfaces (Fig. 4.19). If chloride concentrations are high, a white copper chloride corrosion product may be present beneath the cuprous oxide layer. However, experience shows that copper chloride accumulation is usually slight relative to other corrosion product masses in most natural waters. 

Internal surfaces of all tubes were severely attacked (Fig. 4.29). A brown deposit layer consisting of magnetite, iron oxide hydroxide, and silica covered all surfaces. Deposition was thicker and more tenacious along the bottom of tubes. These deposits had a distinct greenish-blue cast caused by copper corrosion products beneath the deposit. Underlying corrosion products were ruby-red cuprous oxide crystals (Fig. 4.29). Areas not covered with deposits suffered only superficial attack, but below deposits wastage was severe. 

Paradoxically, the most firmly established dihalides of the heavier chalcogens are the dark ruby-red P0CI2 and the purple-brown PoBr2 (Table 16.5). Both are formed by direct reaction of the elements or more conveniently by reducing P0CI4 with 8O2 and PoBt4 with H28 at 25°. 

Form at room Colourless Pale brown Unstable Red brown Ruby red Black... 

Both silver (m.p. 962°C, b.p. 2212°C) and gold (m.p. 1065°C, b.p. 2807°C) have characteristic brilliant white and yellow colours in bulk but when finely divided are black or, in the case of gold, can be purple, ruby red or blue. Thus reduction of gold compounds by SnCl2 gives the colloid known as Purple of Cassius , which is used as a ceramic colorant. 

The halogen chlorides are of course limited to those of Br and I, but although BrCl exists in equilibrium with Cl2 and Br2, it is so unstable that it is not obtained in a pure form. Iodine monochloride is a much more stable compound that exists in two forms. The a form consists of ruby-red needles, and the (3 form is a reddish-brown solid. The forms differ in the way that IC1 molecules are linked by inter-molecular forces in the solid state. 

Anthocyanins usually give a purple red colour. Anthocyanins are water soluble and amphoteric. There are four major pH dependent forms, the most important being the red flavylium cation and the blue quinodial base. At pHs up to 3.8 commercial anthocyanin colours are ruby red as the pH becomes less acid the colour shifts to blue. The colour also becomes less intense and the anthocyanin becomes less stable. The usual recommendation is that anthocyanins should only be used where the pH of the product is below 4.2. As these colours would be considered for use in fruit flavoured confectionery this is not too much of a problem. Anthocyanins are sufficiently heat resistant that they do not have a problem in confectionery. Colour loss and browning would only be a problem if the product was held at elevated temperatures for a long while. Sulfur dioxide can bleach anthocyanins - the monomeric anthocyanins the most susceptible. Anthocyanins that are polymeric or condensed with other flavonoids are more resistant. The reaction with sulfur dioxide is reversible. 

Color can also be induced into colorless crystals by the incorporation of impurity atoms. The mineral corundum, 01-AI2O3, is a colorless solid. Rubies are crystals of A1203 containing atomically dispersed traces of Cr203 impurity. The formula of the crystal can be written (CrvAli r)203. In the solid the Al3+ and Cr3+ cations randomly occupy sites between the oxygen ions, so that the Cr3+ cations are impurity substitutional, CrA1, defects. When x takes very small values close to 0.005, the crystal is colored a rich ruby red. 

The final stage is to control the temperature programme in order to promote the growth of the silver droplets to the size required to produce the yellow colour, in the same way as the production of ruby red glasses. 

Rubidium cobalt sulfate (Rb SO CoSO 6HjO) is an example of several double sulfates that rubidium has the ability to form. Rubidium cobalt sulfate is a combined rubidium-cobalt compound in the form of ruby-red crystals. Other rubidium sulfate crystal compounds and their colors are rubidium + copper = white rubidium + iron = dark green and rubidium + magnesium = colorless. 

The photosensitive nature of selenium makes it useful in devices that respond to the intensity of light, such as photocells, light meters for cameras, xerography, and electric eyes. Selenium also has the ability to produce electricity directly from sunlight, making it ideal for use in solar cells. Selenium possesses semiconductor properties that make it useful in the electronics industry, where it is a component in some types of solid-state electronics and rectifiers. It is also used in the production of ruby-red glass and enamels and as an additive to improve the quality of steel and copper. Additionally, it is a catalyst (to speed up chemical reactions) in the manufacture of rubber. 

Sulfur-selenium phases can be prepared by cooling molten mixtures of the elements either slowly or by quenching followed by extraction with carbon disulfide, carbon tetrachloride or benzene. The crystals are obtained upon evaporation or cooling of the resulting solutions. Their colour deepens from yellow to ruby red with increasing selenium content In the older literature there has been some confusion whether to consider these phases as mixed crystals of discrete Sg and SCg molecules or as binary compounds containing SeS bonds. 

An important application of copper(I) oxide is in antifouling paints for steel, wood, and other materials exposed to sea water. Other applications include manufacture of ruby-red glass and preparation of miscellaneous copper salts. It also is used as a reducing agent in brazing pastes as a fungicide in photocells and as a catalyst. 

Black crystaUine solid exists in two modifications stable black needles known as alpha form that produces ruby-red color in transmitted light, and a labile, metastable beta modification consisting of black platelets which appear brownish-red in transmitted light density of alpha form 3.86 g/cm at 0°C density of beta form 3.66 g/cm at 0°C alpha form melts at 27.3°C, vapor pressure being 28 torr at 25°C beta form melts at 13.9°C hquid iodine monochloride has bromine-hke reddish-brown color hquid density 3.10 g/mL at 29°C viscosity 1.21 centipoise at 35°C decomposes around 100°C supercools below its melting point polar solvent as a hquid it dissolves iodine, ammonium chloride and alkali metal chlorides hquid ICl also miscible with carbon tetrachloride, acetic acid and bromine the solid crystals dissolve in ethanol, ether, acetic acid and carbon disulfide solid ICl also dissolves in cone. HCl but decomposes in water or dilute HCl. 

Such cyanide complexes are also known for several other metals. All the fer-rocyanide complexes may be considered as the salts of ferrocyanic acid H4Fe(CN)e and ferricyanide complexes are that of ferricyanic acid, H3Fe(CN)e. The iron-cyanide complexes of alkali and alkaline-earth metals are water soluble. These metals form yellow and ruby-red salts with ferro-cyanide and ferricyanide complex anions, respectively. A few of the hexa-cyanoferrate salts have found major commercial applications. Probably, the most important among them is ferric ferrocyanide, FeFe(CN)e, also known as Prussian blue. The names, formulas and the CAS registry numbers of some hexacyanoferrate complexes are given below. Prussian blue and a few other important complexes of this broad class of substances are noted briefly in the following sections ... 

The precipitate is washed repeatedly with hot water. Preparation should be in a dark room under a ruby red light. 

The precipitate is washed with hot water. The product is purified by dissolving in ammonia solution, filtering out any insoluble residues, and then adding hydrochloric acid to reprecipitate sdver chloride. Preparation should be carried out in the dark in ruby red light. 

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