All the metals, which precipitate gold from aqua-regia, have been
already shewn to precipitate platina also. As gold is thrown down
by some metallic solutions, as well as by the metals in substance,
particularly those of mercury and iron, it remains to apply these
liquors as precipitants for platina.
1. A saturated solution of mercury in aqua-fortis, which readily and
totally threw down gold in its metallic form, being added to a solution
of platina, the liquor became immediately turbid, and, on standing for
a little time, nearly the whole of the platina fell to the bottom. A
solution of mercury in the marine acid, or of corrosive sublimate,
likewise precipitated platina, but less perfectly, and with this
difference, that the former precipitate was of a greyish brown colour,
the latter of a sparkling red.
2. Solutions of iron in the vitriolic acid, or of common green vitriol
in water, which totally throw down gold, happily made no change in
solutions of platina. Compositions of platina and gold being dissolved
in aqua-regis, the solutions diluted with about twice their quantity
of water, and a filtered solution of the vitriol gradually added; the
mixtures instantly grew turbid, and, on standing, deposited the gold
in form of a purplish grey calx, the whole of the platina remaining
dissolved. It appeared, on numerous repetitions of this experiment,
that no part of the platina was precipitated along with the gold, nor
any of the gold kept suspended with the platina. Where the quantity of
the mixt to be assayed was very small, the precipitation was usually
performed in a filter, that the gold, which separates in very minute
moleculæ, some of which might possibly remain unobserved in the bottom
of a glass, might be detained on the paper. The colourless sorts of
filtering-paper are preferable for this use to the coloured; as these
last may be impregnated with astringent matter, which would extricate
some of the ferrugineous part of the vitriol. The vitriol was dissolved
in about six times its quantity of water, and a few drops of oil of
vitriol added, to prevent the separation of any of its iron in the
filter. This solution was put into the filter first, the solution of
gold and platina immediately poured into it, the whole stirred together
with a clean glass rod, and such part of the liquor, as had run thro’
before they had been duly mixed, poured back to the rest. The gold
remaining in the filter was washed with fresh parcels of water, the
paper cautiously rolled up, and burnt in a crucible, as mentioned in a
former experiment.
3. Solutions of the vitriol, recommended by Kunckel and others for
precipitating gold of an uncommonly high colour, made no change in
the solutions either of gold or platina. The bluish green did indeed
precipitate the gold; not as blue vitriols, but by virtue of the
ferrugineous matter, of which these kinds largely participate. White
vitriol was likewise made trial of, but without producing any sensible
effect in either solution.
4. The experiments with green vitriol were repeated on the solutions of
platina and gold made in spirit of salt. The event was the same as with
those made in aqua-regis; the gold being constantly precipitated, and
the platina remaining dissolved.
+REMARKS+.
It may be proper to observe, that by the processes here pointed out,
the gold is purified from other metallic admixtures at the same time
that it is separated from platina; the inflammable spirits reviving,
essential oils and æther imbibing, and green vitriol precipitating,
gold alone. Care should be had, that the piece of the mixt, taken for
examination, be totally dissolved before any trials are made with
the solution; the menstruum not acting with equal facility on the
two metals, but dissolving the gold more readily than the platina.
Where the acid has been dilute, and only a gentle heat applied, great
part of the gold has appeared to be taken up before the platina was
considerably acted on. Where the filter, with the gold in it, is
burnt in the crucible, borax is the most commodious flux: but as
this salt gives a sensible paleness to gold, a little nitre may be
injected, after the metal has come into fusion, to restore its colour.
If the nitre was added at first, whilst the gold continues subtilely
divided, some particles of the metal would be dissipated during the
deflagration, which that salt produces with the coaly remains of the
paper.
As the foregoing experiments exhibit platina and gold dissolved in
a mineral fluid, which by simple mechanic agitation rejects the one
and retains the other, and which discovers this different appetite of
union so much the more remarkably, as the two metals have been the more
intimately combined:--as they further exhibit platina dissolved in
liquors incapable of holding gold suspended,--gold dissolved in liquors
incapable of holding platina suspended,--gold totally precipitated by
substances, which precipitate no particle of platina,--and gold, when
mixed _per minima_ with platina, perfectly recovered from it by these
means, without increase as well as without diminution:--it follows,
that platina is not, as some believe, gold naturally debased by the
admixture of some other metallic body, but a metal of a peculiar kind,
essentially different from all the others. Before the discriminating
characters of platina were discovered, such a notion was highly
plausible, and direct experiment seemed to confirm it: a portion of
the platina might be separated in the process; a quantity of gold
mixed with the remainder, in order to collect the gold supposed to be
contained in it; the mixture submitted to operations, which gold alone
was supposed capable of withstanding; and the augmentation, which
the noble metal still retained, held to be true gold gained from the
platina.
The methods of trial above related will, it is presumed, be sufficient
to undeceive those, who may have been imposed upon by such appearances,
and betrayed into the practice of unintended frauds: to convince them,
that all they have gained from platina, after the most laborious
attempts to divest it of its imaginary coat, is no other than platina
still: and, which is of more extensive utility, to distinguish all the
abuses, that may be made with this metal, and restore the gold, so
debased, to its original purity and value.
XXI. _An Account of the Temple of_ Serapis _at_ Pozzuoli _in the
Kingdom of_ Naples: _In a Letter to_ John Ward, _LL.D. and R.S.
Vice-Præs. by the Rev._ John Nixon, _M.A. F.R.S._
[Read Mar. 17, 1757.]
+SIR+,
BEFORE we enter upon a more particular consideration of this noble
piece of antiquity, it may not be improper to premise the general
account (and indeed the only one I have met with yet published), which
is given of it by Mess. Cochin and Bellicard, in a little [57]treatise
printed at Paris in 1755. These gentlemen acquaint us, that in 1749
there were only three pillars of this building visible, and that they
were buried half way within the ground: but that soon after, workmen
being employed by order of the King of the Two Sicilies to dig at the
place, they came to the pedestals of those pillars: and at length
discovered the building to have been a temple, which (as it was judged
by the principal[58] idol found there, and some other circumstances)
was dedicated to Serapis. They tell us further, that many statues and
vases of excellent workmanship had been taken out of the ruins; and
that the whole temple was extremely magnificent, being built, or cased
throughout, with marble, even to the parts appropriated to the meanest
offices.
This account, tho’ short, is yet sufficient to excite in the curious
a desire to be more fully informed, both as to the ancient and modern
state of this place. To gratify in some measure that desire is the
purpose of the present letter.
In order to form any conjecture concerning the antiquity of the
building before us, we must know, that the worship of Serapis, to whom
it is supposed to have been consecrated, was not introduced at Rome
till towards the end of the republic; and then tolerated in the suburbs
only[59]. However, at length he was allowed to have temples erected
to him within the precincts of the city; chiefly by the authority of
Vespasian, who was thought to have restored a blind man[60] to his
sight at Alexandria by the aid and direction of this deity. And upon
this account he continued to be held in high veneration by Titus and
Domitian, the sons of that Emperor, as appears by their [61]stamping
his image on the reverse of their coins. Now as it is reasonable
to suppose, that the other cities of Italy followed the example of
the metropolis in this instance, as we find, they did in others of a
similar nature; we may with some probability place the foundation of
this temple at Pozzuoli somewhere within the period assigned above.
As for the particular state of this building, it is situated on the
west side of the town, near to, and upon a level with, the beach (_See_
TAB. II.). Its grand entrance is towards the south, and seems to have
been a vestibule supported by four columns. This introduces you into a
spacious portico, or corridor[62], which was designed to defend such
as assembled here to worship from the injuries of the weather; as also
to afford a commodious passage into a range of rooms of different
dimensions, disposed on all the four sides of the court.
These chambers seem designed for preparing the sacrifices, lodging
the priests, and keeping their vestments; as also the fuel, stores,
and other things requisite for the service of the temple: not to omit
the convenience of purifying both the priests and the worshippers by
bathing or washing. This last destination is countenanced, with regard
to the chamber on the north-west and that on the north-east corner, by
the row of stone seats, which still remains on each of the sides of
the former. These seats have a gutter, or channel running along at the
foot of them on the floor; and are likewise perforated with holes of
a proper size, with funnels passing from them below. On these benches
probably the persons to be purified placed themselves, that the water
might be let out upon them from pipes; or administred in vases or
ewers by the attendants, and afterwards be carried off by the passages
mentioned above[63].
[Illustration: _Philos. Trans Vol. L._ TAB. II. _p. 168._