Bichromate

Chrome Tanning. The original chrome tanning was a two-bath process. The unhaired hides, delimed and bated, were treated with a solution of sodium bichromate [10588-01-9]. The amount of bichromate used was about 3—5% based on the weight of the hides. The bichromate was absorbed or adsorbed into the hide, the solution drained, and the hides refloated. Sodium bisulfite was added and two important reactions resulted in the formation of a basic chromium and coUoidal sulfur in the hide. This gave a chrome taimage and also helped to fiH the hide with the soHd sulfur. This cmde system, which continued in the industry in some types of leather for over 50 years, is obsolete. 

Modem chrome-tanning methods are weU controUed and employ an extensive knowledge of the chemistry of the system. The most common chromium-tanning material used is basic chromium sulfate [12336-95-7] Cr(0H)S04, made by the reduction of sodium bichromate with sulfur dioxide or by sulfuric acid and a sugar. 

Lead chromates are prepared by precipitation techniques from soluble salts ia aqueous media. The raw material Hst iacludes a number of different lead compounds, eg, Htharge, lead nitrate, basic lead acetate, basic lead carbonate, as well as acids, alkahes, sodium bichromate, and sodium chromate. The typical reaction can be represented by the foUowiag equation ... 

Photomechanical stencils are of two types direct coatings and transfer films. Direct coatings are either bichromated gelatin or bichromated poly(vinyl alcohol) (PVA). The coated screens are exposed through a positive, washed, and inspected. These screens are used for printing electronic components. They are not practical for commercial work because of the difficulty of reclaiming the screen after use. 

SODIUM AZIDE SODIUM BICHROMATE SODIUM BIFLUORIDE SODIUM BISULFATE SODIUM BISULFIDE... 

Chemical Designations - Synortyms Ammonium Bichromate Chemical Formula (NH4)2Cr20,. Observable Characteristics - Physical Stale (as normally shipped) Solid Color Orange-yellow bright red-orange orange to red Odor None. 

The quaternary fraction of pot curare, after the removal of some neoprotocuridine, was separated into a portion salted out by sodium bicarbonate, and a portion not so precipitated. The latter was fractionated on a plan described in the original, the most active product obtained being an amorphous iodide with a paralysing dose of 1- 5 mg. per kilo frog. This iodide was phenolic, gave the Millon reaction, but no strychnine-like reaction with bichromate and sulphuric acid. No crystalline product could be isolated, but on complete methylation certain of the fractions yielded crystalline methiodides as follows —... 

If-Phenylenediamine, when warmed with dilute sulphuric acid and potassium bichromate or lead peroxide, gives the odour of quinone (p.-iqa). After warming and cooling, extract with ether. The ethereal solution has a yellow colour. Decant the ether extract on to a watch-glass and leave it to evapoiate in the air. A deposit of microscopic yellow crystals remains. See Appendix., p. 286. 

Or an equivalent quantltj of sodium bichromate (75 qrams), which may be dissolved m 3—4 times its weight of water and delivered from a tap funnej... 

To prepare heliotropin from isosafrol (which results from the isomerisation of safrol with alkalis), 5 parts of isosafrol are treated with a solution of 25 parts of potassium bichromate, 38 parts of cioncentrated sulphuric acid, and 80 parts of water. The reaction product is steam distilled and the distillate is extracted with ether, and the heliotropin obtained is purihed by means of alkaline bisulphite in the usual manner. 

Chrom-gehaltf m. chromium content, -gelatine, /. chromatized gelatin, bichromated gelatin, -gelb, n. chrome yellow (lead chromate) Cologne yellow (lead chromate and... 

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