

Marcu 25, 1915 | 
NATURE 
IOI 

contains gold in the form of. chloride and some free 
hydrochloric acid. Gold is dissolved at the anode, 
under the action of a current of electricity, and de- 
posited in a pure state at the kathode. Other metals 
are also converted into chlorides at the anode, and 
either remain in solution, or pass into the anode slime. 
When silver is contained in the anode, it is converted 
into silver chloride which in part dissolves, in part 
falls to the bottom of the cell, and in part adheres 
to the anode, forming an insoluble coating. The 
result of the coating is that the free area of the anode 
is reduced, the density of the current becomes greater 
per unit area of effective anode surface, and chlorine 
is evolved unless a very small current is used. Accord- 
ing to general experience, if more than 6 per cent. 
of silver is present in the bullion of the anode it is 
necessary to brush the silver chloride from the anodes, 
and accordingly this percentage is seldom exceeded in 
practice. 

Photo) 
The usual amount of free hydrochloric acid present 
in the bath varies from 3 to 10 per cent., but accord- 
ing to the results of experiments now put forward 
by Sir Thomas Rose some advantages are obtained 
by the use of stronger solutions. Thus in a bath 
containing 29 per cent. of free hydrochloric acid, a 
current of 5000 amperes per square metre of anode 
surface can be used without causing chlorine to be 
evolved at the anode. Under these conditions the 
proportion of silver in the anode may be raised to at 
least 20 per cent. without difficulties being encoun- 
tered. The heavy current causes the silver chloride 
to split off from the anode, and also prevents gold 
from entering the anode slime, principally because no 
monochloride of gold is allowed to form. 
Similar advantages occur in the deposition of gold 
at the kathode by the use of a solution containing 
20 per cent. of gold as chloride instead of the usual 
3 to 5 per cent. With a current of 5000 amperes per 
NO. 2369, VOL. 95] 

Fic. r.—Electrolytic gold cells, United States Assay Office, New York. 

square metre, the gold is deposited in a coherent form, 
which is easily washed, and is malleable after being 
melted. The density of current now employed in prac- 
tice is below rooo amperes per square metre, and the 
anodes occupy about a week in being dissolved. With 
a current of 5000 amperes, the anodes would be 
dissolved within the limits of a working day and a 
Saving in interest, and in the difficulties of. daily stock- 
taking, would be effected. : 
One of the merits of the electrolytic process is that 
the refined gold is always malleable and fit for use in 
the arts, and another is that any platinum contained 
in the gold is extracted. This is becoming of some 
importance in view of the high price of platinum and 
of the fact that nearly all rough gold bullion, includ- 
ing that from the Transvaal, is now known to contain 
that metal. According to the experience in the United 
States mints (Fig. 1), it is cheaper to refine gold by 
electrolysis than by sulphuric acid. 
BIRD-MIGRATION 
IN ‘1913.1 
before us 
E have 
/ 
W the ninth of a 
projected series of ten 
reports setting forth the 
imposing mass of data 
regarding bird-migration 
collected by the com- 
mittee appointed for the 
purpose by the British 
Ornithologists’ Club. 
Once the final volume, 
dealing with the autumn 
of 1913 and the spring 
of 1914, has appeared, 
we may expect a pub- 
lication of greater im- 
portance, summarising 
the vast amount of 
material collected by ten 
years’ labour. In the 
meantime no attempt is 
made to draw conclu- 
sions from the facts 
which are published, 
but a few points about 
t he movements of 
1912-13 may here be 
selected for notice. 
The autumn of 1912 
appears to have been 
remarkable for the early 
dates at which the 
migrations of several species began. Thus a swallow 
was noted at the Bell Rock Light in the Firth of Tay 
on July 4, and willow-warblers at the same place two 
days later. As early as June 25 a large flock of 
starlings had been seen flying west in the evening at 
Spurn Head Light. On the nights of July 14-15 and 
15-16 swifts were recorded from the Lundy North 
Light (British Channel) and the Hanois Light 
(Channel Islands) respectively. 
The great movements, however, do not seem to 
have begun until mid-October, and the migrations 
observed during the first three weeks of November 
were of extraordinary magnitude. Almost every night 
during that period half-a-dozen different light-stations 
record the passage of large numbers of birds, notably 
skylarks, starlings, and various species of Turdus. 
1 Report on the Immigrations of Summer Residents in the Spring of 1913; 
also Notes on the Migratory Movements and Records received from Light- 
houses and Light-vessels during the Autumn of 1912.. (Bulletin of the 
British Orn‘thologists' Club, vol. xxxiv., December, 1914.) 
[B. P. Wirth. 
