Chromium history

Chromium. The history of the investigations estabHshing the essentiaHty of chromium has been reviewed (136). An effect of brewer s yeast in preventing or curing impaired glucose tolerance in rats was revealed, and the active factor was identified as a Cr(III) organic complex, glucose tolerance... 

Perhaps more so than any other common metal, the mechanical properties of chromium (8,14—17) depend on purity, history, grain size, strain rate. ... 

The addition of oxides to ceramic bodies and to glasses to produce color has been known since antiquity (2). The use of iron and copper oxides predates recorded history. Cobalt was introduced into Chinese porcelain about 700 AD. Chromium compounds have been used since 1800 AD. 

A wide range of nonacidic metal oxides have been examined as catalysts for aromatization and skeletal isomerization. From a mechanistic point of view, chromium oxide catalysts have been, by far, the most thoroughly studied. Reactions over chromium oxide have been carried out either over the pure oxide, or over a catalyst consisting of chromium oxide supported on a carrier, usually alumina. Depending on its history, the alumina can have an acidic function, so that the catalyst as a whole then has a duel function character. However, in this section, we propose only briefly to outline, for comparison with the metal catalyzed reactions described in previous sections, those reactions where the acidic catalyst function is negligible. 

Reish, D.J. 1977. Effects of chromium on the, life history of Capitella capitata (Annelida Polychaeta). Pages 199-207 in F.J. Vernberg, A. Calabrese, F.P. Thurberg, and W.B. Vemberg (eds.). Physiological Responses of Marine Biota to Pollutants. Academic Press, NY. 

Rolfs CE, Rodney WS (1988) Cauldrons in the cosmos. University of Chicago Press, Chicago Rotaru M, Birck JL, Allegre CJ (1992) Clues to early solar system history from chromium isotopes in carbonaceous chondrites. Nature 358 465-470... 

The publications and correspondence of Bergman and Scheele contain interesting allusions to the de Elhuyar brothers, to Hjelm, and to the early history of the metals tungsten and molybdenum which they discovered. The presence of a new metal in pitchblende was recognized by Klaproth in 1789, but it remained for Peligot half a century later to isolate uranium. Chromium, now the most familiar element of the group, was the last to be discovered when the immortal French chemist Vauquelin finally isolated it in 1798 from a Siberian mineral. For further information about tungsten see pp. 284-301. 

In the tanning process hides are first washed or soaked, hair and keratinous debris are removed, bated (enzymes are used to break down non-collagenous components, which are washed out) and the hide is acid-pickled to prepare for the addition of the chromium salt. Contemporary processes are exclusively based on one-bath procedures and utilize chromium(III). The older two-bath process is now obsolete, mainly because it involved the in situ reduction of chromate, a major environmental and toxicological hazard (cf. chromate toxicity p. 947) to chromium(III) on the hide. A useful review of the history of chromium tannage processes is available.1205... 

Unlike Ziegler catalysts, chromium oxide based catalysts are extremely sensitive to minor changes in the preparation or calcining history. The active sites no doubt respond to the local electronic environment, which determines the molecular weight distribution of the polymer. Therefore, replacing the... 

The hydroxide is usually converted by acids and salts into chromium tetraphenyl salts,1 the fifth phenyl group being split off as phenol or diphenyl. The amount of phenol formed varies apparently with the previous history of the base, homogeneous chromium pentaphenyl hydroxide in its hydrated form giving a 100 per cent, yield of phenol and only traces of diphenyl when treated with a salt such as potassium bromide in the presence of chloroform. The hydrate in absolute alcohol in the complete absence of air affords one molecule of phenol from each molecule of base when acted upon by potassium iodide. The production of phenol probably occurs according to the scheme... 

The next milestone in the history of chromium dyes for wool arose from the observation that 1 1 chromium complex dyestuffs react with a second molecule of a metal-free, tridentate azo compound to give the 2 1 chromium complex. If the second dyestuff is the same as that from which... 

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