100 : REPORT—1905. 
The amalgam will now be entirely liquid at ordinary working tempera- 
tures. On cooling, a crystalline amalgam separates from the liquid, and 
will continue to do so as the temperature is lowered. Cool the amalgam 
to the temperature of melting ice and remove the mother liquid : this is 
the amalgam desired. Itis important that the temperature be truly that 
of melting ice, and that no solid is removed. For convenience the 3 per 
cent. amalgam may be placed in a tubular vessel well surrounded with ice 
shavings ; a long very fine capillary tube reaches to the base of this 
vessel, and through it the liquid at 0° C. is removed by suction. Some 
solid must be left behind, or otherwise there is no certainty of saturation. 
Throughout all the operations neutral cadmium sulphate solution must 
cover the surface of the amalgam and wet all vessels, tubes, &c., through 
which the amalgam passes. Otherwise the amalgam will leave a ‘tail’ 
and its composition may possibly be thereby changed. 
3. Cadmium Sulphate Crystals and Solution, ~_ Procure commercially 
pure cadmium sulphate CdSO,8/3H,O. Dissolve in about 1} time its 
weight of distilled water, agitating either continuously for about six hours 
or occasionally for two or three days. Filter through a fine-grained filter 
paper so as to ensure a clear solution, which should then be placed in a 
number of crystallising dishes and evaporation allowed to take place 
slowly at a temperature not exceeding 35° C., when, provided that dust be 
excluded, many transparent crystals of CdSO,8/3H,O will result. These 
should be prevented as much as possible from adhering to one another by 
removing the liquid to other dishes as soon as the crystals are of such a 
size that most of them are in contact. In this way about five-sixths of 
the liquid may be evaporated, the mother liquid being employed for a pre- 
liminary washing of the mercurous sulphate, the manufacture of which is 
afterwards described. The crystals of cadmium sulphate so obtained 
should be washed with successive small quantities of distilled water until 
after standing for five minutes no trace of acidity can be detected with 
congo red. The crystals, still moist, may then be transferred to a stock 
bottle. To prepare the final solution agitation with distilled water is 
recommended as before, the temperature being preferably 5° or 10° higher 
than the normal temperature, so as to ensure saturation. On no account 
should cadmium hydroxide be employed to neutralise the first solution, 
which is invariably acid ; nor indeed should any attempt be made to 
neutralise the solution except by crystallisation. 
4. Mercurous Sulphate—The preparation in each case is to be con- 
ducted in a darkened room, 
(a) Electrolytic Method.—Pure distilled mercury forms the anode and 
platinum foil the kathode, the electrolyte being dilute sulphuric acid 
(1 part by volume of concentrated acid to 5 parts of distilled water). The 
mercury is preferably placed in the base of a large flat-bottomed beaker 
and about twenty times its volume of the dilute acidadded. Contact with 
the mercury is effected by means of a platinum wire passing through a 
glass tube, while the kathode is suspended in the upper portion of the 
liquid. During the electrolysis the electrolyte must be continually stirred, 
an L-shaped glass stirrer being most efficient, the L portion being placed 
near the surface of the mercury. A current density of about 0:01 ampére 
may be employed. The salt so prepared is treated as per note A. 
(6) Precipitation method, mercurous nitrate and sulphuric acid being 
employed. 
Add strong nitric acid to a little pure mercury contained in a crystal- 
