Purple of Cassius

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← Previous revision Revision as of 10:57, 22 April 2026 Line 7: Line 7: When used as a test, the intensity of the color correlates with the concentration of gold present. This test was first observed and refined by a German physician and alchemist, Andreas Cassius (1600&ndash;1676) of [[Hamburg]], in 1665. [[Berzelius]] later made a detailed study of the purple of Cassius. The colour also attracted attention from [[Michael Faraday]].<ref name=zmond>{{cite book | chapter=Richard Adolf Zsigmondy: Properties of Colloids | title=Nobel Lectures, Chemistry 1922-1941 | chapter-url=http://nobelprize.org/nobel_prizes/chemistry/laureates/1925/zsigmondy-lecture.html | location=Amsterdam | publisher=Elsevier Publishing Company | year=1966 }}</ref> When used as a test, the intensity of the color correlates with the concentration of gold present. This test was first observed and refined by a German physician and alchemist, Andreas Cassius (1600&ndash;1676) of [[Hamburg]], in 1665. [[Berzelius]] later made a detailed study of the purple of Cassius. The colour also attracted attention from [[Michael Faraday]].<ref name=zmond>{{cite book | chapter=Richard Adolf Zsigmondy: Properties of Colloids | title=Nobel Lectures, Chemistry 1922-1941 | chapter-url=http://nobelprize.org/nobel_prizes/chemistry/laureates/1925/zsigmondy-lecture.html | location=Amsterdam | publisher=Elsevier Publishing Company | year=1966 }}</ref>

[[Richard Adolf Zsigmondy]], who earned the 1926 [[Nobel Prize for chemistry]], says that "Several of the red gold divisions prepared with [[formaldehyde]] as well as those reduced with [[phosphorus]] appeared perfectly clear in ordinary daylight (like good [[red wine]]). They did not settle out their gold, and I was therefore able to call them rightly [[chemical solutions]]. In [[Thomas Graham (chemist)|Thomas Graham]]’s [[Dialysis (chemistry)|dialysis]], however, they behaved like [[colloidal suspensions]]: the gold particles did not pass through the [[parchment membrane]]. This showed my gold divisions their proper place, namely, that they belonged to the colloidal suspensions."<ref name=zmond/> [[Richard Adolf Zsigmondy]], who earned the 1926 [[Nobel Prize for chemistry]], says that "Several of the red gold divisions prepared with [[formaldehyde]] as well as those reduced with [[phosphorus]] appeared perfectly clear in ordinary daylight (like good [[red wine]]). They did not settle out their gold, and I was therefore able to call them rightly [[chemical solutions]]. In [[Thomas Graham (chemist)|Thomas Graham]]’s [[Dialysis (chemistry)|dialysis]], however, they behaved like [[colloidal suspension]]s: the gold particles did not pass through the [[parchment membrane]]. This showed my gold divisions their proper place, namely, that they belonged to the colloidal suspensions."<ref name=zmond/>

==References== ==References==