Red, Chrome

The chemical examination of this product is usually limited to a few qualitative tests. A portion is treated with hot dilute hydrochloric acid, and the filtered liquid tested for calcium and sulphuric acid (chalk, gypsum). Another portion is either treated with hot concentrated sulphuric acid or fused with potassium bisulphate when cold the mass is treated with water and the solution tested for aluminium. 

If the product is a paste the dry matter is determined by washing a weighed quantity with hot water and calcining and weighing the residue. 

The principal red and yellow pigments are Lead chromate chrome yellow, orange and red), zinc chromate zinc or buttercup yellow), barium chromate lemon yellow or yellow ultramarine) various products based on jerric oxide, hydrated (yellow) or anhydrous (red), both natural yellow and red ochres) and artificial Mars yellow, English red, etc.) red oxide oj lead minium or red lead) mercuric sulphide cinnabar, vermilion) antimony oxysulphide antimony cinnabar) cadmium sulphide cadmium yellow) basic lead antimonate Naples yellow). 

More rarely use is made for the same purpose of other substances such as strontium and calcium chromates, lead oxychloride (Cassel yellow), lead protoxide, arsenic sulphide (orpiment), stannic sulphide (mosaic gold), potassium cobaltinitrite (cobalt yellow), etc. 

The principal red and yellow colours (when not mixtures) may be distinguished bythe reactions indicated in the scheme on p. 380 the following sections treat of the complete examination of the more important of them. 

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Cbrom rindleder, n. chromed neat s leather, -rot, n. chrome red. -salpetersaure, /. chromonitric acid, -salz, n. chromium salt chromate. 

Prepare about 30 g. of normal lead chromate, PbCr04 (Exercise 23), by the double decomposition of lead acetate and potassium dichromate and wash the precipitate until it is free from soluble lead salts. Suspend the yellow chromate in a dilute solution of sodium hydroxide (1 20) and boil until the color has changed to a bright brick red. This material is a basic chromate known as chrome red, having the composition represented by the formula PbCr04-PbO ... 

Chromate and bichromate of lead—known respectively as lemon and orange chrome, or as chrome yellow and chrome red—yellow ochre, gamboge, and other pigments, furnish a yellow hue. 

Bichromate of Lead—2 PbO, CrOj— chrome red— may bo obtained by boiling oxide of lead, or its car-bonato, with on aqueous solution of monochromate of potassa, or by digesting the neutral chromate of lead in a dilute solution of caustic potassa. Liebig prepared it by adding a neutral ebromate to fased nitre, and washing the residuum it is an insoluble, scarlet colored powder. 

These are based on lead chromate and exhibit all gradations in colour from pale yellow to gamet red, but they may be referred to three principal types chrome yellow, normal lead chromate chrome orange, mixture of normal and basic lead chromates chrome red, basic lead chromate. 

Excess of Lead Oxide in Chrome Orange and Chrome Red.— 1 gram of the substance is treated in the cold with dilute acetic add, which dissolves only the lead oxide not combined as normal chromate in the filtered solution the lead is estimated by the ordinary methods. When no other substances soluble in acetic acid are present, the insoluble part (normal chromate and any extraneous insoluble substances present) may be collected, washed, dried and weighed the lead oxide is then given by difference. 

Cinnabar and vermilion usually contain only small proportions of impurities from the prime materials vermilion may also contain impurities due to the method of preparation, namely, small quantities of metallic mercury, mercuric nitrate and free sulphur. These products are, however, often adulterated with ferric oxide, minium, chrome red, brickdust, gypsum, heavy spar, clay, ammonium chloride, dragon s blood, carmine and artificial organic dyes. Sometimes also arsenic and antimony sulphides are added to modify the colour. 

Acid chrome red, acid anthracene red, acid alizarine red, anthracene chrome red, acid alizarine garnet, azo alizarine Carmoisine, chrome fast Bordeaux, cbrome fast garnet, chromotropes, diamond red, eriochrome red, eriochrome Bor- deaux, omega chrome red, oxychrome garnet, palatine chrome red, eriochrome olive, palatine chrome violet, anthracene chrome violet, acid chrome blue, azi chrome blue, chrome fast blue, chromotrope blue, omega chrome blue. 

Anthracene chrome red, add alizarine red, eriochrome red, eriochrome bordeaux. eriochrome garnet oxychrome garnet, diamond red. palatine chrome red. omega 3 chrome red, etc. i P g.s s 5 r. O 13. 3 a-l Decolorised. Colour is not by air or by perulphatc A for a mordant (C Mordant present. Boll with 5 per cent, sodium aceiate and a small piece of white cotton for two or three minutes. 

Chrome red Basic lead chromate Pb20Cr04 Paint pigment... 

Basic Lead Chromates.—The basic salt, PbaCrOj, PbCrO. PbO, or 2PbO.CrOg, is formed as a red powder by the action of cold caustic soda solution on the normal chromate. It is also produced by mixing together lead chromate and oxide in presence of water, and is known commercially by various names—chrome red, orange chrome, Derby red, Chinese red—according to its depth of colour. It is converted by... 

Lead dichromate PbCr207 Chrome orange chrome red. 

Lead Chromnte(VI) Oxide. Chromic acid lead-(2 + ) salt (1 2) basic lead chromate red lead chromate chrome red chromium lead oxide Persian red Austrian cinnahar CrPb2Os mol wt 546.40. C 9.52%, Ph 75.84%, O 14.64%, PBCrOj PbO See Colour Index vol. 4, (3rd ed., 1971) p 4677. 

W. E. Fuss stated that chrome-red, when ground, acquires a yellow tinge. 

Chrome red. See Lead chromate oxide Chrome scarlet. See Pigment red 104 Chrome titanate. See Chrome antimony titanium buff... 

Synonyms Austrian cinnabar Basic lead chromate Chinese red Chrome orange Chrome red... 

American vermillion n. A pigment usually consisting of a lead molybdate or as a basic lead chromate (as chrome red). 

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