Gold purple

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Colloidal gold solution

Gold purple is a purple colored pigment consisting of finely divided gold . Gold purple was and is used to produce ruby ​​red glass, gold ruby glass .

Gold purple is preferably produced in aqueous solution by the reaction of gold (III) chloride with tin (II) chloride . The resulting solution contains colloidal gold bound to colloidal tin dioxide as a carrier material. This process for manufacturing with tin (II) salt was developed by the German doctor Andreas Cassius , which is why the product containing tin dioxide is named after him Cassius gold purple , Cassius gold or Cassius purple . It is very heat-resistant and does not appear black even in thick layers. Gold purple itself and the use of metallic tin as a reducing agent were known even before Cassius.

use

In addition to the use of gold purple to produce gold ruby ​​glass , it is used in porcelain painting , glazes and for coloring enamel . Today, gold ruby ​​glass is largely being replaced by a cheaper product containing selenium .

The reaction of the formation of gold purple serves as a comparatively sensitive detection of gold salts through the reduction with tin chloride, with a detection limit of 10  ppb .

Properties, color formation

Cassius' gold purple is a colloid of the solid type in colloidal suspension, i.e. a sol. The gold particles are only 4 nm in size. They absorb green and blue light, but let red light through, so that when illuminated with white light, the red color is created. The gold particles are negatively charged due to anion adsorption, which means that they repel each other, so that coagulation is prevented. Larger gold particles give a different color, at 40 nm a blue color develops, see colloidal gold . If the particles become even larger, the gold precipitates.

Historical

Gold ruby ​​glass, which was probably obtained from elemental gold, was already known in ancient times. The much more effective production method of gold purple by reducing gold salts was discovered by Johann Rudolph Glauber . In particular, he discovered that tin is particularly suitable as a reducing agent for gold salts. He wrote in 1659: "put into this Solution dess Gold's a little piece of pure and fine pewter which with no Bley mixed Being intended". He then received the gold "in the form of a purple powder". Johann Christian Orschall published his results on the production of gold purple in 1684, so his work appeared before Cassius 'book of 1685. Cassius' discovery was dated to 1663 or "before 1676". Johannes Kunckel perfected the process of manufacturing gold ruby ​​glass so that he could manufacture it with consistently good quality and in larger quantities, especially around 1679 in a glassworks near Potsdam . Kunckel names Andreas Cassius as the inventor of the gold purple manufacturing process by writing: "It was a Doctor Medicinae, named Cassius, who invented the Praecipitationem ".

Richard Zsigmondy , who received the Nobel Prize in Chemistry in 1925 for his contributions to colloid chemistry, also studied the gold purple. Since the gold and tin dioxide in Cassius' gold purple cannot be separated, Jöns Jakob Berzelius wrongly suspected that it was a gold compound. Zsigmondy therefore produced tin-free gold purple by reducing gold salt solutions with formaldehyde or phosphorus .

Reaction equation

The dissolved trivalent gold is reduced , the bivalent tin oxidizes to tin dioxide . The overall response is:

.

The reduction reaction is:

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The equation of oxidation of tin salt is:

.

literature

Web links

Wiktionary: Goldpurpur  - explanations of meanings, word origins, synonyms, translations

Individual evidence

  1. James B. Calvert: Copper, Silver and Gold. In: Personal Web Sites, University of Denver, Dr James B. Calvert, Physics> Chemistry. March 7, 2004, accessed April 19, 2020 .
  2. a b c d e James B. Calvert: Colloids. In: Personal Web Sites, University of Denver, Dr James B. Calvert, Physics> Mechanics and Thermodynamics. December 9, 2002, accessed April 19, 2020 .
  3. ^ A b c Richard A. Zsigmondy : Properties of colloids. Nobel Lecture, December 11, 1926. In: The Nobel Prize> Nobel Prizes and Laureates> Nobel Prize in Chemistry> 1925. The Nobel Foundation, Nobel Media AB, accessed April 18, 2020 .
  4. a b c d e Leslie Bernard Hunt: The true story of Purple of Cassius: The birth of gold-based glass and enamel colors . In: Gold Bulletin . tape 9 , no. 4 . Springer December 1976, p. 134-139 , doi : 10.1007 / BF03215423 .
  5. ^ A b Johann Rudolph Glauber : Deß Teutschlandts Wolfahrt . In it there are many wonderful and useful things for the best of Vatterland. 4th part (Vierdther part). Prague, Confectio Alkermes Mineralis, p.  519–521 ( reprinted online from 1704 at the Bayerische StaatsBibliothek BSB).
  6. ^ Johann Christian Orschall : Sol Sine Veste. Or thirty experiments to strip gold of its purple: which partly introduces the Destructionem Auri, with attached instruction, to prepare the long requested Rubin-Fluß or Rothe Glaß in highest perfection . Cassel ( reprint from 1742 online at the Bayerische StaatsBibliothek BSB, Munich Digitization Center MDZ).
  7. Andreas Cassius : Andreae Cassii D. Hamburgensis De Extremo Illo et Perfectissimo Naturae Opificio Ac Principe Terraenorum Sidere Auro: De admiranda ejus natura, generatione, affectionibus, effectis, atque ad operationes artis habitudine; Cogitata Nobilioribus experimentis illustrata. Hamburg, X. De Operationibus Circa Aurum Chymics, p.  105 ( [1] at the Bayerische StaatsBibliothek BSB, Munich Digitization Center MDZ).
  8. ^ A b A. F. Holleman , E. Wiberg , N. Wiberg : Textbook of Inorganic Chemistry . 102nd edition. Walter de Gruyter, Berlin 2007, ISBN 978-3-11-017770-1 , p. 1469.
  9. Franz Maria Feldhaus: The technology of prehistoric times: The historical time and the primitive peoples; a handbook for archaeologists ... Wilhelm Engelmann, Leipzig and Berlin 1914, Sp. 480-481 ( online in Internet Archive).
  10. Johannes Kunckel : Collegium Physico-Chymicum Experimentale, or Laboratorium Chymicum . In which clearly and thoroughly of the true principles in nature and the things created [...] are dealt with. Hamburg, Historia, what was invented in this Seculo rares in the Chymie., P.  649–656 ( online at the Bayerische StaatsBibliothek BSB, Munich Digitization Center MDZ).