chloride of aluminum a reduction was effected; the chlorine taking
up the sodium, forming chloride of sodium (common salt), while the
aluminum was left free in the metallic state. It is hardly necessary
to go into the particulars of the process; but a metal well known to
exist, had, for the first time, been brought to the world in such a
condition of structure that its qualities could be tested, not only
chemically, but mechanically. This was the direct result of Deville’s
metallurgic process of obtaining the reducing agent--sodium.
Aluminum in itself would be of but little use, so that a brief
description will be all that is necessary. It is about the color of
silver, but susceptible of a higher polish, especially on a fresh-cut
surface; it is much less susceptible of oxidization than silver; its
specific gravity is but little more than pine wood, and its tenacity,
ductility, and laminating qualities are nearly equal to silver. Its use
in the mechanical arts is limited, notwithstanding all these qualities,
from the fact of its low point of fusibility, and at the heat of
the fusible point being easily oxidized, so much so as to prevent
soldering, except by an autogenous process. But aluminum does possess
a property peculiar to itself--that of forming a purely and strictly
_chemical alloy_ with copper. It unites with it in any proportion;
the compound formed by the addition of 10 per cent. of aluminum to 90
per cent. of copper has been found to possess all the properties of
an entirely new metal, with qualities that render it a very valuable
material in all fine work, such as astronomical instruments; and very
fine machinery, such as watch-lathes, etc.
The French reports on the alloy are somewhat voluminous, but we give
the following.
The color of this bronze so closely resembles that of 18 carat gold,
such as is used for the best jewelry and watch-cases, that it is
capable of receiving the highest polish, and is far superior in beauty
to any gilding.
Samples taken from different parts of the largest castings, when
analyzed, show the most complete uniformity of composition, provided
only that the two metals have originally been properly mixed while in
a state of fusion. These experiments have been made upon cylinders
weighing many hundreds of pounds, and are entirely conclusive.
This valuable quality is not found in any of the more ordinary alloys
of copper. The alloy of copper with tin, for example, known as _gun
metal_, is notoriously subject to a phenomenon known as _liquation_;
in consequence of which a great difference is found in the composition
of the same casting, both in the top as compared with the bottom, and
in the centre as compared with the circumference.
This phenomenon often causes great inconvenience, as the different
parts of large objects will in consequence vary greatly in hardness
as well as in strength. In casting artillery the difficulty becomes a
serious one, and no means have yet been discovered by which it can be
entirely removed.
This homogeneousness of aluminum bronze is a natural consequence of the
great affinity existing between the two metals of which it is composed;
and that there is such an affinity is clearly proved by the phenomenon
attending the manufacture of the alloy. The copper is first melted in
a crucible and the aluminum is then added to it _in ingots_. At first
there is, of course, a reduction of temperature, because the aluminum
in melting absorbs the heat from the melted copper; and this absorption
is so great, in consequence of the great capacity for heat of aluminum,
that a part of the copper may even become solid. But let the mixture
be stirred a moment with an iron bar, and the two metals immediately
unite; and in an instant, although the crucible may have been removed
from the furnace, the temperature of the metals rises to incandescence,
while the mass becomes as fluid as water.
This enormous disengagement of heat, not seen in the preparation of
any other ordinary alloy, indicates, not a simple mixture, but a real
chemical combination of the two metals. The 10 per cent. bronze may
therefore be properly compared to a salt, the more so as it is found by
calculation to contain, within a very minute fraction, four equivalents
of copper to one equivalent of aluminum.
The 10 per cent. bronze may be forged cold, and becomes extremely dense
under the action of the hammer. The blades of dessert-knives are thus
treated in order to give them the requisite hardness and elasticity.
But it has another valuable quality which is found in no other kind
of brass or bronze: it may be forged hot, as well as, if not better
than the very best iron. It thus becomes harder and more rigid, and
its fracture shows a grain similar to that of cast steel. On account
of the hardness of the aluminum bronze, rolling it into sheets would
be a tedious and expensive process, were it not for this property of
being malleable at a red heat. But it may in this manner be rolled into
sheets of any thickness or drawn into wire of any size. It may also be
drawn into tubes of any dimension.
From several experiments made at different times at Paris, it appears
that the breaking weight of the cast bronze varies from 65 to 70
kilogrammes the square millimetre. The same bronze drawn into wire
supported a weight of 90 kilogrammes the square millimetre. The iron
used for suspension bridges, tested in the same manner, did not show an
average of more than 30 kilogrammes. Some experiments were also made by
Mr. Anderson, at the Royal Arsenal at Woolwich, in England, who tested
at the same time the aluminum bronze, the brass used for artillery
and commonly called _gun metal_, and the cast steel made by Krupp in
Prussia. Taking for the maximum strength of the bronze the lowest of
the numbers found as above, we are thus enabled to form the following
table of comparative tenacities:
Aluminum bronze 10 per cent. 65
Crupp’s Cast Steel 53
Refined Iron 30
Brass for cannon 28
The comparative toughness of these same four metals was also tested in
the following manner: A bar of each was prepared of the same size, and
each bar was then notched with a chisel to precisely the same depth.
The bars were broken separately, upon an anvil, by blows from a hammer.
The last three metals in the table broke each at the first blow, with
a clean and square fracture. The aluminum bronze only began to crack
at the eighth blow, and required a number of additional blows before
the two pieces were entirely separated. And the irregular, torn surface
of the fracture showed the peculiarly tough and fibrous nature of the
metal.
The elasticity of the aluminum bronze was tested by M. Tresca,
Professor at the _Conservatoire des Arts et Métiers_. The experiment
was made upon a bar of simple cast metal, and the following is his
report: “The coefficient of elasticity of the aluminum bronze, the
cast metal, is half that of the best wrought-iron. This coefficient is
double that of brass and four times that of gun metal, under the same
conditions.”
The specific gravity is 7.7, about the same as iron. Another very
valuable quality is presented in the fact that it is acted on by
atmospheric influences less than are silver, brass, or bronze. This
places it in the same rank with gold, platinum and aluminum.
Very stiff and very elastic, tougher than iron, very little acted upon
chemically, and in certain cases not at all, capable of being cast like
ordinary bronze or brass, forged like iron and steel, of being worked
in every way like the most malleable metals or alloys, having, added
to these properties, a color analogous to that of the most precious
metal, this bronze proves itself adapted to uses almost innumerable.
At first sight, it seems difficult to admit that the relatively small
proportions of aluminum which enters into the composition of this
bronze can be sufficient to modify so extraordinarily the properties
of the copper which constitutes so large a portion of its weight. But
we must remember that the specific gravity of aluminum is very low,
and that a given weight of this metal possesses a bulk four times as
large as the same weight in silver. It follows from this that the ten
per cent. of aluminum contained in the bronze equals in bulk forty per
cent. in silver.
The specimens of the ware we have seen, such as spoons, forks, cups,
watch-cases, etc., are certainly very beautiful, having the color and
high polish of gold, while dilute acids do not affect the surface.
On the Reduction of Silver in the Wet Way.
Every chemist is familiar with the reduction of chloride of silver
in the form of powder by means of metallic zinc in the presence of a
little free acid. It is not easy to bring two such substances as the
silver salt and the metal into close contact, and after the work is
accomplished the removal of the excess of zinc has its difficulties.
Dr. Grager suggests a modification of the old method that ought to
be more generally made known. The chloride of silver is dissolved
in ammonia and poured into a well-stopped bottle, and into this is
introduced an excess of metallic zinc, in not too small fragments, so
that any reduced metal adhering to it may be readily washed off.
The decomposition begins immediately, and is rapidly accomplished,
especially if the contents of the flask be well shaken up. Three hours
will suffice to reduce one-quarter of a pound of chloride of silver.
It is easy to ascertain when the reduction is ended, by testing a
portion of the ammoniacal solution with hydrochloric acid. As soon as
no cloudiness or curdy precipitate is formed, the work may be regarded
as completed.
A slight excess of ammonia is said to be favorable. The reduced silver
must be washed with water until all odor of ammonia has disappeared.
The pieces of zinc are removed by pouring the contents of the flask
through a funnel, the opening of which is too narrow for the passage
of the zinc fragments, while the reduced silver can be easily washed
through. The finely divided silver can be digested in hydrochloric
acid to restore it to a pure white color, and it is then ready for
solution or fusion, and will be found to be perfectly pure. In dealing
with large quantities it would be economical to recover a portion of
the ammonia by distillation. In the same way an ammoniacal solution
of nitrate of silver can also be reduced by zinc, and the silver
obtained pure, even when the original solution of the nitrate contains
copper--provided a small quantity of silver be kept in the bath.
It is better where copper is present not to take all of the zinc that
may be requisite for the reduction of the silver. It will prove a
great convenience to be spared the necessity of converting the silver
into the chloride, as it is no easy task to wash out this salt on
filters--and it will be found to be applicable to alloys which do not
contain more than 25 per cent. of silver.--_From Prof. Joy in the
Journal of Applied Chemistry._
Transcriber’s Notes
Obvious errors in punctuation have been fixed.
Page 7: “Mechanique Celeste” changed to “Méchanique Céleste”
Page 12: “ou rexperience” changed to “our experience”
Page 18: “head-quarters far astronomical observations” changed to
“head-quarters for astronomical observations”
Page 22: “it accomodates” changed to “it accommodates”
The Table of Contents lists “Equation of the Time Table” as the article
on page 28. The actual article is named “On the Reduction of Silver in
the Wet Way.” This has intentionally been left as per the original.
Similarly, there is no actual section titled “Notices of New Tools”
despite its inclusion in the Table of Contents, and this has been left
as per the original.