Lead oxide melted or incompletely vitrified is still in common use in
the manufacture of inferior earthenware, and sometimes leads to
serious results. To detect lead in a glaze, M. Herbelin moistens a
slip of white linen or cotton, free from starch, with nitric acid at
10 per cent. and rubs it for ten to fifteen seconds on the side of the
utensil under examination, and then deposits a drop of a solution of
potassium iodide, at 5 per cent. on the part which has been in
contact. A lead glaze simply fused gives a very highly colored yellow
spot of potassium iodide; a lead glaze incompletely vitrified gives
spots the more decided, the less perfect the vitrification; and a
glaze of good quality gives no sensible color at all.--_M. Herbelin._
* * * * *
ON THE ELECTRICAL FURNACE AND THE REDUCTION OF THE OXIDES OF BORON,
SILICON, ALUMINUM, AND OTHER METALS BY CARBON.[1]
[Footnote 1: Read at the recent meeting of the American
Association, Ann Arbor, Mich.]
By EUGENE H. COWLES, ALFRED H. COWLES, AND CHARLES F. MABERY.
The application of electricity to metallurgical processes has hitherto
been confined to the reduction of metals from solutions, and few
attempts have been made to effect dry reductions by means of an
electric current. Sir W. Siemens attempted to utilize the intense heat
of an electric arc for this purpose, but accomplished little beyond
fusing several pounds of steel. A short time since, Eugene H. Cowles
and Alfred H. Cowles of Cleveland conceived the idea of obtaining a
continuous high temperature on an extended scale by introducing into
the path of an electric current some material that would afford the
requisite resistance, thereby producing a corresponding increase in
the temperature. After numerous experiments that need not be described
in detail, coarsely pulverized carbon was selected as the best means
for maintaining a variable resistance and at the same time as the most
available substance for the reduction of oxides. When this material,
mixed with the oxide to be reduced, was made a part of the electric
circuit in a fire clay retort, and submitted to the action of a
current from a powerful dynamo machine, not only was the oxide
reduced, but the temperature increased to such an extent that the
whole interior of the retort fused completely. In other experiments
lumps of lime, sand, and corundum were fused, with indications of a
reduction of the corresponding metal; on cooling, the lime formed
large, well-defined crystals, the corundum beautiful red, green, and
blue hexagonal crystals.
Following up these results with the assistance of Charles F. Mabery,
professor of chemistry in the Case School of Applied Science, who
became interested at this stage of the experiments, it was soon found
that the intense heat thus produced could be utilized for the
reduction of oxides in large quantities, and experiments were next
tried on a large scale with a current from two dynamos driven by an
equivalent of fifty horse power. For the protection of the walls of
the furnace, which were made of fire brick, a mixture of the ore and
coarsely pulverized gas carbon was made a central core, and it was
surrounded on the sides and bottom by fine charcoal, the current
following the lesser resistance of the central core from carbon
electrodes which were inserted at the ends of the furnace in contact
with the core. In order to protect the machines from the variable
resistance within the furnace, a resistance box consisting of a coil
of German silver wire placed in a large tank of water was introduced
into the main circuit, and a Brush ammeter was also attached by means
of a shunt circuit, to indicate the quantity of current that was being
absorbed in the furnace. The latter was charged by first filling it
with charcoal, making a trough in the center, and filling this central
space with the ore mixture, which was covered with a layer of coarse
charcoal. The furnace was closed at the top with fire brick slabs
containing two or three holes for the escape of the gaseous products
of the reduction, and the entire furnace made air-tight by luting with
fire clay. Within a few minutes after starting the dynamo, a stream of
carbonic oxide issued through the openings, burning usually with a
flame eighteen inches in height. The time required for complete
reduction was ordinarily about an hour.
The furnace at present in use is charged in substantially the same
manner, and the current is supplied by a Brush machine of variable
electromotive force driven by an equivalent of forty horse power. A
Brush machine capable of utilizing 125 horse power, or two and
one-half times as large as any hitherto constructed by the Brush
Electric Company, is being made for the Cowles Electric Smelting and
Aluminum Company, and this machine will soon be in operation.
Experiments already made so that aluminum, silicon, boron, manganese,
magnesium, sodium and potassium can be reduced from their oxides with
ease. In fact, there is no oxide that can withstand temperatures
attainable in this electrical furnace. Charcoal is changed to
graphite. Does this indicate fusion or solution of carbon? As to what
can be accomplished by converting enormous electrical energy into heat
within a limited space, it can only be said that it opens the way into
an extensive field for both pure and applied chemistry. It is not
difficult to conceive of temperatures limited only by the capability
of carbon to resist fusion. The results to be obtained with the large
Brush machine above mentioned will be of some importance in this
direction.
Since the cost of the motive power is the chief expense in
accomplishing reductions by this method, its commercial success is
closely connected with the cheapest form of power to be obtained.
Realizing the importance of this point, the Cowles Electric Smelting
and Aluminum Company has purchased an extensive and reliable water
power, and works are soon to be erected for the utilization of 1,200
horse power. An important feature in the use of these furnaces, from a
commercial standpoint, is the slight technical skill required in their
manipulation. The four furnaces in operation in the experimental
laboratory at Cleveland are in charge of two young men twenty years of
age, who, six months ago, knew absolutely nothing of electricity. The
products at present manufactured are the various grades of aluminum
bronze made from a rich furnace product that is obtained by adding
copper to the charge of ore, silicon bronze prepared in the same
manner, and aluminum silver, an alloy of aluminum with several other
metals. A boron bronze may be prepared by the reduction of boracic
acid in contact with copper.
As commercial results may be mentioned the production in the
experimental laboratory, which averages fifty pounds of 10 per cent.
aluminum bronze daily, and it can be supplied to the trade in large
quantities at prices based on $5 per pound for the aluminum contained,
the lowest market quotation of this metal being at present $15 per
pound. Silicon bronze can be furnished at prices far below those of
the French manufacturers.
The alloys which the metals obtained by the methods above described
form with copper have been made the subject of careful study. An alloy
containing 10 per cent. of aluminum and 90 per cent. of copper forms
the so-called aluminum bronze with a fine golden color, which it
retains for a long time. The tensile strength of this alloy is usually
given as 100,000 pounds to the square inch; but castings of our ten
per cent. bronze have stood a strain of 109,000 pounds. It is a very
hard, tough alloy, with a capacity to withstand wear far in excess of
any other alloy in use. All grades of aluminum bronze make fine
castings, taking very exact impressions, and there is no loss in
remelting, as in the case of alloys containing zinc. The 5 per cent.
aluminum alloy is a close approximation in color to 18 carat gold, and
does not tarnish readily. Its tensile strength in the form of castings
is equivalent to a strain of 68,000 pounds to the square inch. An
alloy containing 2 or 3 per cent. aluminum is stronger than brass,
possesses greater permanency of color, and would make an excellent
substitute for that metal. When the percentage of aluminum reaches 13,
an exceedingly hard, brittle alloy of a reddish color is obtained, and
higher percentages increase the brittleness, and the color becomes
grayish-black. Above 25 per cent. the strength again increases.
The effect of silicon in small proportions upon copper is to greatly
increase its tensile strength. When more than 5 per cent. is present,
the product is exceedingly brittle and grayish-black in color. It is
probable that silicon acts to a certain extent as a fluxing material
upon the oxides present in the copper, thereby making the metal more
homogeneous. On account of its superior strength and high conductivity
for electrical currents, silicon bronze is the best material known for
telegraph and telephone wire.
The element boron seems to have almost as marked an effect upon copper
as carbon does upon iron. A small percentage in copper increases its
strength to 50,000 or 60,000 pounds per square inch without
diminishing to any large extent its conductivity.
Aluminum increases very considerably the strength of all metals with
which it is alloyed. An alloy of copper and nickel containing a small
percentage of aluminum, called Hercules metal, withstood a strain of
105,000 pounds, and broke without elongation. Another grade of this
metal broke under a strain of 111,000 pounds, with an elongation
equivalent to 33 per cent. It must be remembered that these tests were
all made upon castings of the alloys. The strength of common brass is
doubled by the addition of 2 or 3 per cent. of aluminum. Alloys of
aluminum and iron are obtained without difficulty; one product was
analyzed, containing 40 per cent. of aluminum. In the furnace iron
does not seem to be absorbed readily by the reduced aluminum when
copper is present; but in one experiment a mixture composed of old
files, 60 per cent.; nickel, 5 per cent.; and of 10 per cent. aluminum
bronze 35 per cent., was melted together, and it gave a malleable
product that stood a strain of 69,000 pounds.
When the reduction of aluminic oxide by carbon is conducted without
the addition of copper, a brittle product is obtained that behaves in
many respects like pig iron as it comes from the blast furnace. The
same product is formed in considerable quantities, even when copper is
present, and frequently the copper alloy is found embedded in it.
Graphite is always found associated with it, even when charcoal is the
reducing material, and analysis invariably shows a very high
percentage of metallic aluminum. This extremely interesting substance
is at present under examination.
* * * * *