truck running under the crucible. The bars of silver are then cut to
suitable lengths and rolled to the required thickness of the coin in
rollers worked by machinery. The rough ends are again cut off, and
two portions of the size of a shilling are taken from each strip of metal
and sent forward for assay. Until these results are finished, the strip
cannot be sent on, and if the assay is not satisfactory, the metal is
remelted. The strips of metai, about a yard and a half long, if containing
the proper percentage, are conveyed on wooden trucks to the
cutting-room. Here discs of metal of thé size of a shilling are cut out
of each strip at the rate of 500 a minute, and two machines were at
this work when I was there. The waste from the cutting of the circular
discs is sent back to the melting-pot, and the discs are transferred
to a machine to give them the edge. Any discs which have sustained
injury while passing through the various machines are picked out
and sent back to the melting-pot. The machines which give the edge
to the coin turn out at the rate of 800 a minute. On emerging from
these machines, the metal is very brittle and requires annealing. The
discs are therefore placed in pots and heated in an annealing furnace for
about an hour. They are then taken out and thrown into sawdust, from
which they are separated by sieves. Here they are afterwards packed
on tracks and sent to the stamping-room, where they are stamped
and milled in eight machines, which,turn out thirty shillings a minute.
Again packed on tracks, the coins are transferred to the weighing-
rooms. Balances worked by steam and fed by a long hopper weigh
the shillings at thirty per minute. After weighing, they drop down
a glass tube and into a box provided with three compartments—one
for coins that are too heavy, the centre one for medium, or proper
weight, coins, and one for those which are too light in weight. According
to their weight they fall into one or other of these three compartments,
and are thus separated. The heavy and light coins are
returned to the melting-pot, and the medium ones are sent to the
Bank of England.
The assaying of the samples of metal is performed in a small
laboratory in another portion of the building. Gas muffles are used
for the cupolations, and seventy-four cupels are put in one furnace at
once. The methods of cleaning the buttons and hammering before
weighing are both peculiar to the Mint, and Professor Roberts, in
drawing my attention to these details, said, “ I t is upon such
matters as these that success and failurê depend.”
I t will be especially interesting to my readers to be reminded, in
connection with this semi-technical sketch of refining and coining in
England, that in some parts of the United States the method of parting
gold by nitric acid is still in use, notably at the San Francisco
mint. There, the properties of gold being first determined by assay,
one part ,of gold is made up, and two parts- of granulated silver are
added. The metal is then transferred to earthen - receptacles capable
of holding 130 pounds in each jar. Nitric acid of thirty degrees’
strength is added, and the jars are placed in hot water to facilitate the
action. When the action of the acid is at an end, the jars are filled
up with water, and the weak solution of argentic nitrate formed is run
off from the subsided gold. The finely divided gold is washed in a
filter several times. I t still contains silver, in order to remove which
it is boiled with concentrated sulphuric acid, two pounds of acid being
added for every pound of gold. The sulphate of silver is removed, and
the gold, after repeated washing, is dried. The solutions of nitrate of
silver are precipitated with common salt, and the argentic chloride
formed is reduced with zinc. The purity of the resulting metal is
about 991 per 1000 for the gold, and 998 per 1000 for the silver. In
England the nitric acid parting method has almost entirely been superseded
by the chlorine process, which, there is no doubt, is more economical
and more effective than any other acid methods, whether sulphuric
or nitric acids. Parting by acids is never complete ; the gold always
contains traces of silver, and the silver always traces of gold; more
complete separation is undoubtedly obtained by the chlorine process.
Only one firm in England still uses the nitric acid process. In
America the process is used by a few firms which have a ready market
for the gold in the finely divided state furnished by the nitric acid,
method, and it is for this reason, of course, that it is employed.
YII.
On a Thursday night (March 3rd, 1881), two years
to the day prior to receiving the telegraphic news of
his death, I sat in the midst of a great throng of
scientific men in the theatre of the Chemical Society at
Burlington House, to hear Frank read two papers before
the Society, under the presidency of Professor H. E.
Roscoe. The subjects were*: (1) “ On the Action of
Bacteria on Yarious Oases,” and (2) “ On the Influence
of Intermittent Filtration through Sand and Spongy