Hall marks on gold & silver plate

ASSAY. : WASTE AND SWEEP. 137
ASSAY BY MEANS OF THE SPECTROSCOPE.
Before concluding our account of the Assay Offices of the
United Kingdom, we may here briefly notice the new system of
assay of the precious metals by means of the spectroscope, recently
proposed by Mr. J. Norman Lockyer, F.R.S. Experiments have
been conducted at the Mint to ascertain the practicability of the
scheme and determine whether it would be possible to it. adopt Mr.
the aid
Roberts, Chemist of the Mint, expresses an opinion that by
of the spectroscope differences of composition more minute than the
Tooou^h part might be readily distinguished.
The Deputy Master of the Mint (Mr. C. W. Fremantle), in his
Mr. Roberts
report for the year 1873, states that he had requested
to render every assistance to Mr. Lockyer in developing a process
of quantitative spectrum analysis, which might with advantage re-
place the methods of assay, or at any rate of verification, in use at
the Mint. Experiments conducted by Mr. Lockyer and Mr. Roberts
were continued throughout the early part of the year, and the results
were communicated in a paper to the Royal Society, who have directed
their publication in the "
Philosophical Transactions." As,
however, these researches were of the nature of laboratory experiments
merely, it became necessary to conduct a series under conditions
more nearly approaching those which would occur in actual
practice, and instructions were given that such experiments should
be conducted in the Mint itself. Instruments have been obtained,
and arrangements have now been completed for this branch of the
work.
WASTE AND SWEEP.
The sweep is composed of cinders or dust from the forge, the
sweepings of the workshop, broken crucibles, the dross which adheres
to the ingots of metal after fusion, and of every waste which
can possibly contain minute particles of gold and silver, which had
escaped the notice of the workman, or had become dispersed and
lost in the manipulation of the metals.
This sweep is washed over a fine hair sieve, and the more per-
ceptible portions of metal separated and refined ;
but the remainder
is called by the French les regrets, yet contain impalpable particles,
and is usually sold to persons who have the necessary utensils and
appliances, and who, by means of mercury mills, about the size of a
coffee mill, burning it in the crucible, and by the employment of
fluxes of saltpetre, etc., are able to extract whatever metal may remain.
It is then cupelled to determine the proportions of gold and
silver eliminated in the process.
In large establishments the waste and sweep form a considerable
item. We may especially notice the coinage operations at the
London Mint. The large gold coinage which commenced in 1871,
and was finished in June, 1873, amounted to ,^24,500,000 sterling.
The value of the metal actually deficient during the operation was