Burlington free press. [volume] (Burlington, Vt.) 1827-1865, 1843-05-26

cables, and the construction of suspension or
chain bridges, the first Of which n grand
scale was finished by MIR. Teford in 1925 This
bridge, which crosses the straight of Menai,
connects the island Of m lesea to the mainland,
and is 800 IN length between its points Of
pension, and 100 above the water, thus allowing
! large vessels to pass under it. 1t is composed Of
Tour IRON ropes, each consisting of four chain
strands, with road way between each pair of
ropes The ends of the chains pass over rollers
on towers of considerable height, and are secu r.
ed to iron bars buried under an immense mass
| OF masonry. As chains Of such weight could
| not be stretched level, they hang in an inverted
arch, and the roadway is suspended to them by
IRON rods shortest at the centre, and increasing
in length towards the ends, so that the passage
is perfectly level Another quite recent use Of
wrought iron is for the construction of ships
| having their hus entirely of rolled iron plates.
| The iron steam ship building at Bristol in Eng.
land, and now nearly ready for will be the
largest vessel atloat her clear burthcn exceeding
3OG0 tons. She has been often described in
the public papers, that it would be super1uous
to enter into the details of her construction
! Several vessels of iron have been some years in
use, but their qualities can hardly be considered
as fully tested. Their supposed advantages are
greater strength, durability, incombustbility,
freedom from vcrmin, increased space for stow
| age, uniformity Of temperature and lightncss,
the actual weight of largo iron ship being hum
drcds Of tons less than that of wooden one Of
the same dimensions. With regard to the
parative strength of iron and wooden ships,
some recent occurrences seem to have shewn
that the supposed superiority of the former in
this respect, upon the present plan of construc.
ton, is at least doubtful.
The extended use Of quicksilver in the mod.
ern arts is so important, that it ought not to pass
unnoticcd Its employment in the form of an
amagam for sverng mirrors is familiar, but
its most important uses in gliding, and IN the
extraction Of the precious metals The most re-
markable property of this metal is its power of
uniting with other metals in the form called
amalgan, and then separating from them by
heat, which drives off the mercury in vapour, at
a temperature of between six and seven hum
| drcd degrees. In gliding metals, the amalgam
of gold and quicksilver is applied, and adheres
to the surface of the object, which is then ex-
posed to the proper heat, and the quicksilver
vapourizes, leaving the gold in the form of
I thin film firmly attached to the metal. The ex-
! traction Of the precious metal from their ores
by quicksilver depends upon the same property.
The levigatcd ore is mingled with quicksilver,
which amalgamatcs with the metal leaving the
various mineral substances, with which it is nat.
| urally combined, and the metal is separated from
the quicksilver by heat,or sometimes by pressure
in leathern bag, the quicksilver escaping
through the pores of the leather. This property
| of mercury, and its resemblance to melted silver,
| from which its name is derived, quicksilver sig.
nfyny living silver early attracted the attention
of the alchemists, and sanguine hopes were
| long entertained of discovering process for
| lidiying the fluid metal or fixing it it was
termed, and thus producing true silver. But
the alchemis,s did not limit their aspirations to
the fixing of mercury. They believed gold to
be the true base of all metals, and expected to
be able to recover it by means of an universal
solvent, and this was for very long period the
principal object of chemical research. These
| dreams a n m Of E,urODe IN.
ny centuries, and the hope of accomplishing the
trnnsmutation of metals was not abandoned I'M
til about the close of the seventeenth century,
To the misguided abonrs of the alchemlsts
modern chemistry owes much, but it was mere
cropping emprlcsm, until higher aims guided
It's researches, and raised it to the rank Of lib.
cral science.
Chemistry has revealed the existence of nu-
mcrous metals unknown to former ages, and
they are found to enter largely into the compo-
sltion of almost every known substance. Most
otthesc metals assume visible existence only in
in the laboratory of the chemist, but one of them
is already Of considerable use in the arts, and
promises to become yet more valuable. alude
| to platinum, first found only in South America,
but lately more abundantly in Siberia, which
now furnish the principal supply to COM
merce, Platinum is nearly as heavy as gold, but
harder and much more difficult OF fusion. 1t
forms an excellent material for crucibles and boil
already noticed, for rejecting specula. The
loss of the precious metals in coin by abrasion
or wear has led 70 the employment OF platinum
| in coinage hy the Russ an Government. If this
metal could be obtained in sufficient quantity, It
rht be advantagcousiy substituted for other
me ais a circulating medium, but while gold
silver, and copper continue to be coined, the adj
dtIon of platinum money, by making the stand
| ard of value Quldruplicate, must increase the
serious Inconvenience already resulting from
the iluctuating value of gold aud silver.
The wastage of the precious metals by abra-
son, and their consumption and loss IN the va
rious purposes to which they are applied in a
STAG of minute division, have lately been the
Slhicct of much investigation. What processes
may be going on in natures vast laboratory to
repair this loss, we are Ignorant but the known
sources of supply are by no means sufficient for
! the increasing demand, which of course Is atten-
dfd with Increasing wastage and consumption.
Considerable quantities of gold silver and pla-
tinnm are consumed in various chemical opera
tons, and large quantities of the two former
metals rrecovcrably lost in gliding and sill
vc5ug But the principal source of loss is from
abrasion Every one must have observed that
old coin are lighter than new, and that by long
circulation the Impression becomes first worn,
and finally ohtera,cd The loss upon gold com
is much less than that upon silver, and the diff
ference, which is in the ratio of one 10 four, Is
I chiefly owing to the greater care taken ot the
former, ana the more RAPID circulation OF the lat
! ter especially in small coin, which wear much
! faster than larger ones. Jacobs estimates the an
nual average loss of gold and silver coin by abra
sion at the rate of one part in four hundred
andtwenty and III, total amount of less he.
tween 1909 and lS2i at about ninety millions
of dollars. Gold and silver are very largely used
also for watch cases. personal ornaments, and va
rous small articles of convenience, aud the use of
silver for spoons forks, and other table furniture
has been lately much augmented. The same au-
thor supposcs that gold and silver were with
drawn from circulation, and converted into uten-
sils and ornaments, to the amount of about twen-
ty eight millions of dollars during the same Pc
Rod All these articles, and especially those of
silver, are exposed to greater degree of wear
than even coin, and of course the loss by abrasion
is greater in proportion.
[Concuded next week,
| Wa ronfess that Mr. CLAW is mora Of , ma,