Silver, 100 illus

In treating of the making of gold, silver or electrum, there is no illusion as to any transmutation of the baser metals into precious metals. Their purpose is to produce an imitation that for practical purposes of the jeweler s trade will pass for the more expensive materials and yet will cost less. 

With respect to the aims of the alchemists he expresses himself in his Treatise on the Metals and Alchemy. He cherishes no illusions as to the possibility of the making of real gold or silver, and asserts that their pretended gold and silver can easily be shown by cupellation to be false. Nevertheless he says,... 

A model of the structure must be fit to the map. This used to be done with the "Richards box", a device containing a half-silvered mirror to give the illusion of superposition of a physical model and the electron density map (conventionally contoured in serial sections, traced onto transparent film, and stacked (17).) Recently, some protein structures have been determined using interactive computer graphics to fit a stick model of a structure to an electron density map (18, 19). 

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