82 REPORTS ON THE STATE OF SCIENCE. 
kathode, the electrolyte being dilute sulphuric acid (1 volume of acid to 
5 volumes of water). The mercury is placed in the bottom of a large 
flat-based beaker and about twenty times its volume of the dilute acid is 
added. Contact with the mercury is made by a platinum wire passing 
through a glass tube, and the kathode is suspended in the upper portion 
of the liquid. During electrolysis the electrolyte must be continually 
stirred, an L-shaped glass stirrer being very efficient, the foot of the 
L moving close to the surface of the mercury. A convenient current 
density is 0°01 ampere per square centimetre of anode surface. The 
mercurous sulphate so prepared is filtered and the greater part of the 
raercury removed ; it is then washed with dilute sulphuric acid and 
saturated cadmium sulphate solution in a manner already described for 
the previous preparation. 
(2) By means of Fuming Sulphuric Acid.—Place distilled mercury in 
a erystallising dish so as just to cover the bottom. Add sufficient fuming 
sulphuric acid to flood the surface of the mercury to a depth of about 
2 millimetres. Cover with a clock glass and place on one side for 48 hours. 
Mercurous sulphate is formed and appears in the crystalline form. Care- 
fully add the salt to hot dilute sulphuric acid (1 to 6) and well agitate. 
Decant the hot liquid. If any caked masses of the sulphate are left, these 
should be rejected or crushed in an agate mortar. Wash three times by 
decantation with hot dilute sulphuric acid, and afterwards filter and 
wash with saturated cadmium sulphate solution in the manner already 
described. Set aside with cadmium sulphate solution for one week at 
least, test for acidity, and wash as described for the first preparation. 
The Mercurous Sulphate Paste.—The mercurous sulphate is mixed with 
about one-fourth its volume of powdered recrystallised cadmium sulphate, 
and about one-tenth its volume of pure mercury. (When the electrolytic 
sulphate is used, or that prepared with fuming sulphuric acid, no mereury 
need be added.) To the mixture of mercurous sulphate, cadmium sulphate, 
and mercury, sufficient saturated cadmium sulphate solution is added, so 
that when well mixed the whole forms a thin paste. 
Setting up the Cell.—That type of H-form of cell which may be 
hermetically sealed is the most convenient ; if the lower end of each 
limb is slightly constricted, the contents of the cell are less liable to be 
disturbed. The platinum wires inside the glass vessel are amalgamated 
by passing an electric current from a platinum wire anode through an 
acid solution of mercurous nitrate to each of the wires in turn as a 
kathode. ‘The vessel is washed out twice with dilute nitric acid, several 
times with water, and finally with distilled water ; it is dried in an oven. 
A small pipette is used for the introduction of the amalgam, and a small 
thistle funnel for the insertion of the paste and crystals. The main stock © 
of amalgam is flooded with very dilute sulphuric acid, and it is melted 
over a water-bath ; a little of it is introduced into one of the limbs of 
the H-vessel. After the amalgam has solidified, this limb must be washed - 
out several times with distilled water, care being taken to avoid wetting 
the interior of the other limb. A little distilled water is added and the 
amalgam is melted by immersing the limbs of the H-vessel in hot water. 
After the solidification of the amalgam, it is washed once more with 
distilled water. Into the other limb sufficient mercury is introduced to 
cover the amalgamated platinum wire ; then the paste is added, care being 
taken not to smear the sides of the vessel. Finally, powdered crystals 
of cadmium sulphate are introduced into each limb, and saturated 
