prov:value
| - The element selected from the group consisting of tin, germanium and lead may be introduced in the form of such compounds as tin chlorides, bromides and nitrate, lead halides, nitrate, acetate and carbonate, germanium chloride and oxalate, in aqueous solution, or preferably in the form of tin, germanium and lead alkyl-, cycloalkyl or aryl-metals, such as, for example: tetrabutyl tin, tetramethyl t
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