Kiihne (D.R.P. 147,871) described a process in which external heating is not necessary, a mixture of aluminium turnings, sulphur and boric acid being ignited by a hot iron rod, the resulting aluminium sulphide, formed as a by-product, being decomposed by water.
It is usually to be met with in the form of turnings or raspings, the former being obtained in the maufacture of the "bitter cups" which are made of this wood.
The precipitation is effected by zinc in the form of bright turnings, or coated with lead, or by electrolysis.
The gold and other metals are precipitated on the under surfaces of the turnings and fall to the bottom of the compartment as a black slime.
The slime is cleaned out fortnightly or monthly, the zinc turnings being cleaned by rubbing and the supernatant liquor allowed to settle in the precipitating boxes or in separate vessels.
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