will be obtained. In order to assist the secondary electro- lysis various electrolytes may be added. In the simplest case, the corresponding acid is added to the solution of the electrolyte. Here a considerable part of the metal is deposited primarily. This method is employed in the following analysis : for the deposition of cadmium (slightly acid (H2SO4) solution, ^ = 70 — 80**, current density per square decimetre, Z> = 0*6 — 1 amp.), copper (solution con- — 1*5 amp, in warm or cold solution ; in sulphuric acid solution the addition of 05 gram of hydroxylamine sulphate, or 1 gram of urea, assists the formation of a good, coherent deposit ; chlorides must be entirely absent), mercury (5 per cent, nitric acid, D = 0*5 amp.), bismuth (deposited as amalgam when the solution contains a corresponding quantity of mercury salt ; if the electromotive force is less than 1*3 volts only mercury is separated), platinum (with 3 per cent, of sulphuric acid gives a coherent deposit at t = 65° and J) = 005, but platinum black (or sponge) at the ordinary temperature when Z> = O'l — 02, E = 1*2 volts), and palladium (conditions the same as for platinum).
In other cases double salts are used. The double salts of nickel and cobalt with ammonium sulphate give good deposits in ammoniacal solution (30 — 40 c.c. of ammonia solution, t = 50°, i> = 0*5 — 1*5) according to Fresenius and Beigmann.
The majority of the heavy metals give with ammonium oxalate double salts which are suitable for deposition. The methods in these cases have been mostly worked out by Classen (4). In depositing iron, the absence of nitrates is essential. The solutions should be kept slightly acid with oxalic acid when zinc, cadmium, copper, and tin are being separated. An equivalent quantity of ammonium oxalate is about the amount to be added to the salt solution.
The following metals are deposited in this manner: — Iron (^ = 20 - 40^ 2> = 1 - lo, JP = 36 - 43 volts), cobalt
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