If the zinc is present as blende, this operation offers considerable difficulties, because in the roasting process the zinc sulphide passes in the first instance into sulphate, which demands a high temperature for its conversion into oxide.
In 1853 works were established for the manufacture of white oxide of zinc from a calamine found here, in the next year metallic zinc was produced, and in 1865 the first sheet zinc made in America was rolled here.
By both these methods the single potential-differences found at the surfaces of the zinc and copper have opposite signs, and the effective electromotive force of a Daniell's cell is the sum of the two effects.
Richter in 1863, and of gallium, detected in certain zinc blendes by Lecoq de Boisbaudran in 1875.
Hence, if we assume that, in the Daniell's cell, the temperature coefficients are negligible at the individual contacts as well as in the cell as a whole, the sign of the potential-difference ought to be the same at the surface of the zinc as it is at the surface of the copper.
The deposition of pure zinc is beset with many difficulties.
When the zinc and copper plates are connected through a wire, a current flows, the conventionally positive electricity passing from copper to zinc in the wire and from zinc to copper in the cell.
In the form of a powder, it is obtained by reducing the oxide with zinc and extracting with soda, or by dissolving out the manganese from its alloys with tungsten.
Distilled with zinc dust morphine yields phenanthrene, pyridine and quinoline; dehydration gives, under certain conditions, apomorphine, C17H17N02, a white amorphous substance, readily soluble in alcohol, either and chloroform.
The ketenes are usually obtained by the action of zinc on ethereal or ethyl acetate solutions of halogen substituted acid chlorides or bromides.