+--------+---------------+-------+--------+----------+--------+
| Metal. |Denomination of|Length.|Breadth.|Thickness.|Average |
| |intended coin. | | | |Weight. |
+--------+---------------+-------+--------+----------+--------+
| | |Inches.|Inches. | Inches. |Troy oz.|
|Gold | Sovereign | 24 | 1·375 | 1·000 | 320 |
| | Half-Sovereign| 24 | 1·125 | 1·000 | 250 |
+--------+-----------------------+--------+----------+--------+
| | Crown | 22 | 2·750 | 1·000 | 300 |
| | Half-Crown | 22 | 2·500 | 1·000 | 240 |
| | Florin | 21 | 2·125 | 1·000 | 220 |
|Silver | Shilling | 21 | 1·437 | 1·000 | 150 |
| | Sixpence | 21 | 1·125 | 1·000 | 120 |
| | Fourpence | 21 | 0·875 | 1·000 | 96 |
| | Threepence | 21 | 0·875 | 1·000 | 96 |
+--------+-----------------------+--------+----------+--------+
| | Penny | 24 | 2·500 | 0·375 | 100 |
|Bronze | Halfpenny | 24 | 3·000 | 0·375 | 117 |
| | Farthing | 24 | 3·000 | 0·375 | 117 |
+--------+---------------+-------+--------+----------+--------+
It is to be regretted that crowns, half-crowns, and fourpences are no
longer coined. It has been represented to me by many manufacturers and
others who employ vast numbers of men, that the disuse of the fourpenny
piece has caused considerable inconvenience in the weekly payments to
their workpeople. The objection to this coin would appear to be that it
is so nearly the diameter of the threepenny piece; but this is obviated
by the fact that the edge of the latter is plain, while that of the
fourpenny is crenated or “milled.”
The assay pieces,[14] when cut from the bars, are placed in the
divisions of a tray going from left to right, so that there can be
no mistake as to the number of the pot from which the metal comes;
each assay piece is then placed in a small envelope, marked with a
distinctive mark, to characterise the pot from which it came. The assay
pieces are sent in equal numbers to the two non-resident assayers,
who determine, irrespectively of each other, the amount of gold found
in each piece. Suppose we trace one assay piece, and imagine that 120
are undergoing the same process at the same time. The assay piece is
flattened out into a kind of ribbon, and from it three pieces are cut,
each weighing half a gramme. Each piece of this weight takes the name
of a _thousand_, and is represented by the figures 1,000; but of course
it may be called a pound, a ton, or by any other denomination. Each
piece is wrapped in paper, with three times its weight of silver in two
pieces, both metals being of the same thickness. The parcels, as they
may now be called, are ready for the next process, and are arranged
in their proper places from left to right in the divisions of a tray,
and taken to the assaying furnace. In the assaying furnace is placed a
Payen[15] muffle, or kind of oven, perforated at places so as to allow
a limited amount of atmospheric air to pass from the interior through
its sides into the furnace. The muffle is surrounded with fuel, so that
it is kept at a good—almost white—heat. On the floor of the muffle is
sprinkled some bone ash—obtained by burning bones to whiteness—and on
this bone ash is placed a set of 40 cupels, or little cups, made of
compressed bone ash, and about as big as a florin, and so deep as to
hold about half a teaspoonful of water. When the cupels have been in
the muffle long enough to become red hot, a piece of lead of about nine
times the weight of the gold to be assayed is put into each cupel,
taking care not to let any lead fall over, or it would destroy the
muffle. So soon as the lead has melted, the paper parcels containing
the gold and the silver are placed one in each cupel of melted lead.
In a short time the gold and silver melt together, and, as it were,
dissolve in the lead; then a kind of circulation of the fluid metallic
mixture is observed to take place; and during this circulation, the
lead, as it is presented to the surface, meets with the oxygen of the
atmosphere, and combining with it, forms oxide of lead, which at that
temperature is fluid, and drains into the substance of the cupel,
carrying with it the copper and other impurities contained originally
in the gold, leaving in the cupel a button which contains all the pure
gold and the silver. The cupellation occupies about ten minutes, and
at the end of that time the little mass of fused metal is observed to
brighten up, the signal by which the assayer knows that the process is
finished, and he withdraws the cupels one by one, tilting the fluid
globule on one side, that it may incorporate with it any small globule
which may chance to be upon the side of the cupel. Some assayers
close the doorway of their muffles as the time of the brightening up
of the assay approaches, to avoid the access of the atmosphere till
the buttons have become solid, because the button of metal—by its
silver—absorbs oxygen; and giving off this oxygen at the moment of
solidification, spurts or opens, leaving the button hollow or ragged.
This precaution is not thought necessary by all assayers, nor, indeed,
is this system invariably followed, for some prefer to wrap the gold
and silver in the lead foil which is to be used, and do not care to
have the precious metals of identical thickness; these assayers use a
smaller proportion of silver, viz., 15 parts to 6 of standard gold,
or 17·50 to that which they judge to be _fine_, with a view to avoid
the danger of “spurting;” they also save time by withdrawing the whole
batch of cupels on a tray by means of a peel. The button is taken from
the cupel as soon as it has been detached, either by dropping a little
water on to it, or by allowing it to cool spontaneously, and it is
then hammered out into a strip and annealed. It is next rolled into
a ribbon or fillet, and again annealed, after which it is curled up
into the form of a letter S. Some prefer to roll the piece into a kind
of cushion, but in such a case it is more difficult to remove all the
silver; the proper plan is to expose as large a surface as possible to
the action of the acid in the next operation.
[Footnote 14: See pages 9, 53.]
[Footnote 15: That is, made by Payen, of Paris.]
The S-shaped fillet is put into a flask of nitric acid of specific
gravity 1·23, and the flask is placed in a little cup of brass,
which stands over a small gas-burner, while the neck of the flask
enters a kind of flue, through which a current of air is continually
passing into the chimney of the furnace. The flask being placed in
its position, the gas is lighted, and a gentle heat applied, when the
nitric acid dissolves out the silver from the S-shaped fillet, and is
known to have done its work when red fumes cease to be evolved. The
acid is then poured off, and the remaining sponge of metal is washed
with distilled water, and boiled with concentrated nitric acid, which
removes the remainder of the silver. The sponge of gold is now washed
with water, to remove the nitrate of silver, and is then heated to
redness in a capsule to render it tough, for in its spongy state it is
so rotten that it will not bear to be touched; and although it remains
spongy, it is toughened by being heated to redness. It is now called
a _cornet_. This spongy state is a consequence of the addition of
silver, the presence of which, and its subsequent removal, produce a
separation of the particles of the gold. The gold is thus formed into
a kind of network or sponge, so that the acid can get at every part of
it, and remove any metal which is soluble in the acid. Diluted acid
is used first, because if there be any lead left it is dissolved out,
and because the action of the strong acid is so violent, that part of
it would probably be carried out from the flask. Nitric acid, when
boiling, is liable to form bubbles of gas, which expanding, give rise
to what is called _bumping_; hence it is usual to put a charred pea
into the flask, and this, floating on the surface, causes a more even
flow of vapour and gases, and so prevents bumping. It is probable that
the charred pea determines the boiling at one particular temperature,
for it is found that water, if it be floated in a fluid of a higher
boiling point than itself, may be raised considerably above its
ordinary boiling point, although remaining quiescent till disturbed
by a rod or point. The cornet is next weighed, and as it has been
begun under the idea that it was a _thousand_—1,000—all that it weighs
short of 1,000 is the alloy which has been removed, the object having
been to determine how much pure gold was present in the alloy. There
is, however, a source of error in the process which requires to be
explained.
It is found to be practically impossible to remove every trace of
silver from the cornet; it is therefore necessary to make an allowance,
the amount of which is determined by a _proof_. The proof consists of
a mixture of gold and silver of known proportions, so that if all the
silver be removed from a thousand—1,000—the remaining cornet should
weigh exactly 916·6. Four of these proofs are worked with each batch of
assays—a batch being 120 assays—under precisely similar circumstances,
every precaution being taken that the four shall be equally distributed
over different parts of the furnace, &c. Now suppose that the proofs,
instead of weighing 916·6, as they would weigh if the whole of the
silver were removed, were found each to weigh 916·9; it would be known
that 000·3 of silver had been retained, and must be deducted from each
of the whole batch of assays. If the assays of coins exceed the limits
of from 917·6 to 915·6, they are repeated, as it is assumed that an
error has arisen. The convenience of considering the ½ gramme as 1,000
consists in the fact that 1,000 parts of standard gold contain 916·67
of gold and 83·33 of alloy; so that the result having been arrived at
without any calculation, one source of error is avoided and time is
saved.
Messrs. Johnson, Matthey, and Co. have invented a tray of platinum
capsules or thimbles, into which the assay pieces are placed for
treatment with acid, instead of into the ordinary glass vessels over
gas-burners. The advantages of this invention are too manifest to
require elaboration; but saving of acid, gas, labour, and risk of
error are amongst the chief of them; and besides, the plan has been in
successful operation in their own assay offices in Hatton Garden, as
well as in other important assay offices, for several years past. The
first cost would seem to be the principal objection to this plan of
Messrs. Johnson, Matthey, and Co.; but this is really a small matter,
for the apparatus becomes stock in trade, and its cost should be
viewed simply as so much capital, whose interest is paid by the saving
effected in glass, but more especially by the smaller amount of acid
actually employed, while the platinum can at all times be sold for
nearly its original cost as old metal.
The mode of operation is as follows:—A stand of slate is so arranged
that a means of heating is made to rest on its base. For this purpose
a jet of gas is preferred; where, however, gas cannot be obtained,
an ordinary oil lamp or a charcoal fire may be used. On a shelf over
the source of heat are placed two or three receptacles of platinum,
each communicating with a vessel made of porcelain, provided with
three necks and an overflow pipe. There is a kind of sieve or tray of
platinum, so arranged as to carry from 16 to 100 thimbles of platinum,
and provided with a handle, so that this tray, with its charge, can be
manipulated at pleasure. The thimbles vary in size according to taste,
but each one is cut or slit at the bottom, so that the solution of
silver as it is formed may by its density fall out, and allow the clean
acid to take its place.
When an operation is to be performed, the tray filled with the charged
thimbles—that is, containing the assay pieces—is placed in one of the
platinum receptacles or boilers, and heated to a fitting temperature;
when the desired effect is produced, the tray is lifted into another
receptacle, and again heated; this may be carried to three times if
necessary. The products of decomposition of the acid go, with the acid
which evaporates, into the porcelain vessel, where the free acid falls
through the overflow pipe into a proper chamber, while the acid fumes
pass into the flue through the third neck before spoken of. The parted
assays having been washed by several immersions in boiling distilled
water, without removal from their thimbles, have now to be dried and
annealed in a platinum muffle, so formed as to fit into an ordinary
muffle, and, after annealing, to be weighed in the usual manner, having
saved at least 75 per cent. of the usual trouble.
It is almost needless to add that the system of _proofs_ above
described must be also used with this process.
The assay for silver is not so tedious, as it is finished at the point
where it leaves the muffle on the cupel; but up to this point it passes
through precisely the same process as the gold.
It will have been observed that the event of the process of assaying is
to exhibit the proportion of _bullion_ which may be present in a given
weight of mixed metals, but that it does not demonstrate the character
of the substance which forms the alloy, because this is assumed to
be copper or silver. In practice it is found that the alloy may be
a mixture of copper or silver with lead, mercury, antimony, arsenic,
tin, or zinc, in varying proportions, but whose sum does not exceed the
rate per centum in relation to the bullion which is allowed by law. The
existence of minute proportions of lead, mercury, antimony, arsenic,
tin, or zinc is a matter of great concern, for these, when present, add
indefinitely to the difficulties of the coining departments.
Under the present system, complete analyses of bullion imported for
coining are a practical impossibility. I would therefore propose to
abolish the office of non-resident assayer, and then to appoint two
resident assayers, who should conduct their operations in independent
laboratories—already existent—and a condition of whose appointment
should be an agreement to conduct, when so directed by the Master
of the Mint, complete analyses of the bullion submitted for assay.
The information thus obtained would enable the melter, by processes
subsequently explained,[16] to remove all those substances which
are _now_ found to be fatal to the coining of certain bullion. The
appointment of officers possessing such ability would be an equal
guarantee with the present for the faithful preservation of the
integrity of the coinage. This suggestion has been adopted and
recommended—so far as regards the resident assayers—by Messrs. C. W.
Fremantle and C. Rivers Wilson, in their “Reports on the Mint,” 1870.
Indeed two assistant assayers have been recently appointed.
When the assay reports arrive, the Master determines whether the metal
has been found within the limits, and if he be satisfied he writes on
the assay reports “Passed,” and signs the reports. The Deputy-Master
retains the reports as his warrant, and then issues his order for the
delivery of the bars by the melter to the rolling room, as recommended
in my report dated 29th January, 1859; but, as the accounts are kept by
weight, every set of bars is weighed by the officer who receives them
into that room before he gives them to his men to work into fillets.
When, in 1856, I took charge of some departments in the Royal Mint,
I found that the system of weighing was extremely loose. Officers
were plainly told that if they ventured to satisfy themselves as to
the weight of bullion they had received—in fact, to determine whether
they received what was charged to them—“they would be paid out.” This
state of things led men to accept _any_ weight. But I objected and
resisted; for I found that the average on each day’s work as received
amounted to an habitual minus of five ounces on the weight charged
on silver, while on gold it was seldom so little as one ounce. In
illustration I will state one case which occurred. I delivered 7920·00
ounces of gold to the Mint Office. When that gold was received,
the official weigher gave me credit for 7918·15 ounces, which was
a deduction of no less than 1·85 ounces. I appealed to the Master,
who by written order directed the gold, the weight of which was thus
disputed, to be weighed by Mr. Pilcher, the officer of the weighing
room, in the presence of witnesses whom the Master nominated. Mr.
Pilcher complied with this order, and gave a certificate, signed by
the deputed witnesses, in which he stated that the gold under dispute
weighed 7919·98 ounces—that is, that it differed in weight as charged
by me to the Mint Office 9·60 grains instead of 888·00 grains, the
difference which the official weigher had deducted from the bullion
I had delivered to him. The custom had been to weigh silver to 0·50
ounce, and gold to a pennyweight; but I introduced the system of
weighing silver to 0·10 ounce, and gold to 0·01 ounce, and at the same
time induced the Master to order new balances of superior construction
for the coining department, and one specially devised by Mr. James M.
Napier for use in the Mint Office. Of this balance, received after
having been ordered for some years, it will be sufficient to say that
it appears to be extremely accurate when properly used, and is then
capable of great results; but, unfortunately, the system is such that
those who are admittedly unfit may be promoted to important posts, just
because they are senior, and not because of superior fitness for the
work. This fine balance, therefore, becomes equal to a good rifle in
the hands of a bad marksman. Great accuracy having been enforced, the
weighing is now improved, but is still far from perfect, because the
officers are compelled to abide by the decision of the weigher at the
Mint Office, who, as beforesaid, may be unfit for his office, while
the officers themselves are debarred from all checks, by the removal
from the coining department of the set of standard weights, which were
bought on purpose that those gentlemen might check their own weights as
to accuracy. The Master’s order for the removal of these weights was in
the following terms:—
[Footnote 16: See pages 81-82.]
“The standard weights hitherto kept in the weighing room
are permanently transferred to the Mint Office. A new set
of standard weights to be made for the Mint Office. The
coining department weights to be examined by Mr. ——
——, and compared with those in the Mint Office (after
these have been corrected), and reported on by him. Such
examinations to be repeated every six weeks.”
It should be observed that this order was preceded by one written on
the 2nd February, 1865, which directed that the Mint Office weigher
should be the final judge, but that any officer might demand the
re-weighing of any bullion, while the second weighing was to be final.
All appeals to pass through Mr. John Graham, the order proceeding to
direct that—
“The final decision is not to be called in question by any
other officer of the coining department.”
The latter determination, I was informed, was intended to apply to me
personally. Its immediate effect was a deduction of 0·25 ounce from the
first gold I delivered, and a consequent alteration of my book to that
extent by Mr. John Graham, who made a note in writing as follows:—
“This difference (error) may be accounted for by the
acknowledged error of three grains heavy of the Mint Office
500 oz. weight. See Œrtling’s Report.
(Signed) “J. G.”
Such being the circumstances, I submitted; but the result could be in
one direction only, for it had long been maintained that the reported
losses were but “an hallucination,” and were, in fact, a “mere
difference of weighing.”
It is true that the weights are periodically adjusted, but there is
adjusting and adjusting. These facts have been dwelt upon because
they have a most important bearing on the subject of loss and gain by
coining, to be afterwards treated of.
Between 1856 and 1866 the old scales were removed, to make room for
the superior balances of Messrs. De Grave, Short, and Fanner, the
eminent scale-makers of St. Martin’s-le-Grand, of whose balances it
is impossible to speak too highly, and of whom it is but fair to
state that the Prize Medal was awarded to them at the International
Exhibition, 1862, for their superior workmanship in balances.
Since it is necessary for the officer in charge of any department to
ascertain the exact amount he gives to his workmen, and to satisfy
the Master that they have returned—to within the limit of the weight
of one blank of whatever denomination of coin he may be working—the
bullion which they received, it became imperative to select the best
balance; and in practice that made by Mr. S. R. Short, of the firm
above named, was found to be the most serviceable. Mr. Short has
introduced minor improvements from time to time, as experience has
dictated, but the balance about to be described, after years of wear,
determines to within one grain when charged with 1,200 ounces troy. The
mode of proving the accuracy of a balance is to weigh as usual, and
having arrived at a just determination of the weight of the matter to
be weighed, to change the weights to the pan in which the matter has
been weighed, and to place the matter in the pan previously occupied by
the weights, so that both are now made dependent from the reverse ends
of the beam; if the results be identical with the former results there
can be no doubt as to the accuracy of the beam; should there be any
variation, the balance must be adjusted by minute alterations of the
knife-edges at its ends.
Mr. Napier has made his balance after the principle of Mr. Cotton’s
balance, so that it requires no adjusting screws, but I have no
personal experience of the benefits of this omission.
[Illustration: IMPROVED BALANCE (TO WEIGH 2000 OUNCES.)