Scientific American Supplement, No. 433, April 19, 1884

V >> Various >> Scientific American Supplement, No. 433, April 19, 1884

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Let us now compare these figures with some actual cases, taking as
an example a system of incandescent lighting. In these systems the
difference of potential between any two points of the circuit outside of
the lamps does not exceed 150 volts. Taking this figure, therefore, it
will be seen that under no circumstances can the shock received from
touching these wires become dangerous--not even by touching the
terminals of the dynamo itself; because in neither case can a current be
driven through the body, sufficient to cause an excessive contraction of
the muscles.

In a system of arc lighting, however, we have to deal with entirely
different conditions; for, while in the incandescent system the adding
of a lamp, which diminishes the resistance, requires no increase of
electromotive force, the contrary is the case in the arc light system.
Here every additional lamp added to the circuit means an increase in
resistance, and consequent increase in electromotive force or potential.
Taking for example a well known system of arc lighting, we find that the
lamps require individually an electromotive force of 40 volts with a
current of 10 amperes. In other words, the difference in potential at
the two terminals of every such lamp is 40 volts. Consequently, if the
circuit were touched in two places, including between them only one
lamp, no injurious effects would ensue. If we touch the circuit so as
to include two lamps between us, the effect would be greater, since the
potential between those two points is 2 x 40 volts. We might continue
in this manner touching the circuit until we had included about 7 or
8 lamps, when the shock would become fatal, since the point would be
reached at which the difference of potential is great enough to send a
dangerous current through the body.

Up to this point we have assumed that, while touching two points in the
wire, the rest of the circuit is perfectly insulated, so that no current
can leak, in other words, that the circuit is nowhere "grounded." If
this is not the case we may, under suitable conditions, receive a
shock by touching only _one_ point of the wire. This becomes clear
by considering the current to leak from another spot of different
potential, to pass through the ground and into the body; thus, on
touching the wire the body virtually makes a connection between the
two points of the circuit. In clear dry weather such leaks are
insignificant; but in damp and rainy weather, and with poor insulation,
they may rise to such a point at which it would be dangerous to touch
the circuit even with one hand, the leaks being sometimes so great as
to cause the lamps to burn in a fitful, desultory manner, and to go out
entirely.

There is still another factor which enters into the discussion of the
danger of electric light wires. This must be looked for in the fact that
the physiological effects are greatest at the moment of the opening or
the closing of the circuit; or in a closed circuit they are the more
marked when the flow of current stops and starts, or diminishes and
increases. In dynamo electric machines the current is not absolutely
continuous or uniform, since the coils on the armature being separated a
distance cause a slight break or diminution of the current between each.
This break is so short that it does not interfere with the practical
work for lighting; in some constructions, nevertheless, the distances
apart is so great that, while not interfering with light, its effects
upon the muscles are greatly increased over those of other constructions
which give a more uniform current.

All these statements might lead to the conclusion that arc light wires
are dangerous under any circumstances; but this is not the case. The
first and only requisite is, that they be perfectly insulated. When thus
protected accidents from them are impossible, and all mishaps that have
occurred through them can be traced directly to the lack of insulation.
Nevertheless, we would warn our readers against experimenting upon arc
wires by actual trial, because unforeseen conditions might lead to
disagreeable results.

* * * * *

ROBERT CAUER'S STATUE OF LORELEI.

The statue of Lorelei, the mythical siren of the Rhine, represented in
the annexed cut, which is taken from the _Illustrirte Zeitung_, was
modeled by Robert Cauer, of Kreuglach on the Rhine. He was born at
Dresden in 1831, and is the son of the well-known sculptor Emil Cauer,
and a brother of the sculptor Karl Cauer.

[Illustration: LORELEI STATUE BY ROBERT CAUER.]

* * * * *

REDUCING AND ENLARGING PLASTER CASTS.

Ordinary casts taken in plaster vary somewhat, owing to the shrinkage of
the plaster; but it has hitherto not been possible to regulate this
so as to produce any desired change and yet preserve the proportions.
Hoeger, of Gmuend, has, however, recently devised an ingenious method
for making copies in any material, either reduced or enlarged, without
distortion.

The original is first surrounded with a case or frame of sheet metal or
other suitable material, and a negative cast is taken with some elastic
material, if there are undercuts; the inventor uses agar-agar. The usual
negative or mould having been obtained as usual, he prepares a gelatine
mass resembling the hektograph mass, by soaking the gelatine first, then
melting it and adding enough of any inorganic powdered substance to give
it some stability. This is poured into the mould, which is previously
moistened with glycerine to prevent adhesion. When cold, the gelatine
cast is taken from the mould, and is, of course, the same size as the
original. If the copy is to be reduced, this gelatine cast is put in
strong alcohol and left entirely covered with it. It then begins to
shrink and contract with the greatest uniformity. When the desired
reduction has taken place, the cast is removed from its bath. From
this reduced copy a cast is taken as usual. As there is a limit to the
shrinkage of the gelatine cast, when a considerable reduction is desired
the operation is repeated by making a plaster mould from the reduced
copy, and from this a second gelatine cast is taken and likewise
immersed in alcohol and shrunk. It is claimed that even when repeated
there is no sacrifice of the sharpness of the original.

When the copy is to be enlarged instead of reduced, the gelatine cast is
put in a cold water bath, instead of alcohol. After it has swollen as
much as it will, the plaster mould is made as before. For enlarging,
the mould could also be made of some slightly soluble mass, and then by
filling it with water the cavity would grow larger, but it would not
give so sharp a copy.

* * * * *

STRIPPING THE FILM FROM GELATINE NEGATIVES.

We have frequent inquiries as to the best means of removing a
gelatino-bromide negative from its glass support so that it can be used
either as a direct or reversed negative, and it does not appear to be
very generally known that about two years ago Mr. Plener described a
method which answers well under all circumstances, whether a substratum
has been used or not.

If a negative is immersed in extremely dilute hydrofluoric acid
contained in an ebonite dish, say half a teaspoonful to half a pint of
water, the film very soon becomes loosened, and floats off the glass,
this circumstance being due to the solvent action which the acid
exercises upon the surface of the plate as soon as it has penetrated the
film. If the floating film be now caught upon a plate which has been
slightly waxed, and it is allowed to dry on this plate, it will become
quite flat and free from wrinkles. To wax the plate, it should be held
before the fire until it is moderately hot, after which it is rubbed
over with a lump of wax, and the excess is polished off with a piece
of flannel. When the film is dry, it will leave the waxed glass
immediately, if one corner is lifted by means of a penknife. The film
will become somewhat enlarged during the above-described operation; but,
by taking suitable precautions, this enlargement may be avoided. It is
also convenient to prepare the hydrofluoric acid extemporaneously by the
action of sulphuric acid on fluoride of sodium; and, in many cases, it
is advisable to thicken up the film by an additional layer of gelatine.

The following directions embody these points. The negative, which must
be unvarnished, is leveled, and covered with a layer of warm gelatine
solution (one in eight) about as thick as a sixpence. This done, and
the gelatine set, the plate is immersed in alcohol for a few minutes
in order to remove the greater part of the water from the gelatinous
stratum. The next step is to allow the plate to remain for five or six
minutes in a cold mixture of one part of sulphuric acid with twelve
parts of water, and in the mean time two parts of sodium fluoride are
dissolved in one hundred parts of water, an ebonite tray being used. A
volume of the dilute sulphuric acid equal to about one-fourth of the
fluoride solution is next added from the first dish, and the plate
is then transferred to the second dish, when the film soon becomes
liberated. When this is the case, it is placed once more in the dilute
sulphuric acid. After a few seconds it is rinsed in water, and laid on a
sheet of waxed glass, complete contact being established by means of a
squeegee, and the edges are clamped down by means of strips of wood held
in position by American clips or string. All excess of sulphuric acid
may now be removed by soaking the plate in methylated alcohol, after
which it is dried. It is as well to add a few drops of ammonia to the
last quantity of alcohol used.

The plate bearing the film negative is now placed in a warm locality,
under which circumstances a few hours will suffice for the complete
drying of the pellicular negative, after which it may be detached
with the greatest ease by lifting the edges with the point of a
penknife.--_Photo. News_.

* * * * *

NEW ANALOGY BETWEEN SOLIDS, LIQUIDS, AND GASES,

By W. SPRING.

The author asks in the first place, What is the cause of the different
specific gravities of one and the same metal according as it has been
cast, rolled, drawn into wire, or hammered? Does the difference observed
prove a real condensation of the matter under the action of pressure, or
is it merely due to the expulsion by pressure of gases which have been
occluded when the ingot was cast? According to well-known researches,
metals such as platinum, gold, silver, and copper, which have
been proved to occlude gases on fusion, and to let them escape,
_incompletely_, on solidification, are precisely those which are
most increased in their specific gravity by pressure. The author has
submitted to pressures of about 20,000 atmospheres metals which possess
this property, either not at all, or to a very trifling extent, and he
finds that though a first pressure produces a slight permanent increase
of density, its repetition makes little difference. Their density is
found to have reached a maximum. Hence the density of solids, like that
of liquids, is only really modified by temperature. Pressure effects
no permanent condensation of solid bodies, except they are capable of
assuming an allotropic condition of greater density. The author's former
researches tend to show that solid matter, in suitable conditions of
temperature, takes the state corresponding to the volume which it is
compelled to occupy. Hence there is an analogy between the allotropic
states of certain solids and the different states of aggregation of
matter. Possibly the different forms of matter may be due to a single
cause--polymerization. The limit of elasticity of a solid body is the
critical moment when the matter begins to flow under the action of the
pressure to which it is submitted, just as, e.g., ice at or below 0 deg. may
be liquefied by strong pressure. A brittle body is simply one which does
not possess the property of flowing under the action of pressure.

* * * * *

HYDROGEN AMALGAM.

Hydrogen, although a gas, is recognized by chemists as a metal, and when
combined with any solid metal--as in the case known to electricians as
the polarization of a negative element,--the compound may correctly be
termed an alloy; while any compound of hydrogen with the fluid metal
mercury may with equal correctness be termed an amalgam of hydrogen, or
"hydrogen amalgam." The efforts of many chemists and mining engineers
have for many years been devoted to a search for some effective and
economical means for preventing the "sickening" of mercury and its
consequent "flouring" and loss. Some sixteen or more years ago,
Professor Crookes, F.R.S., discovered and, after a series of
experiments, patented the use of an amalgam of the metal sodium for this
purpose. He made the amalgam in a concentrated form, and it was added
in various proportions to the mercury used for gold amalgamation. Water
becoming present, it will readily be understood that the sodium, in
being converted into the hydrate (KHO) of that metal, caused a rapid
evolution of hydrogen. The hydrogen thus evolved was the excess over a
certain proportion which enters into combination with the mercury. While
the mercury retained the charge of hydrogen, the "quickness" of the
fluid metal was preserved; but upon the loss of the hydrogen the
"quickness" ceased, and the mercury was acted upon by the injurious
components contained in the ore.

Since the introduction of the sodium amalgam, many attempts have been
made, more especially in America, to overcome the tendency of mercury to
"sicken" and lose its "quickness." The greater number of these efforts
have been made by the use of electricity as the active agent in
attaining this end; but such efforts have been generally of a crude and
unscientific character. Latterly Mr. Barker, of the Electro-amalgamator
Company, Limited, has introduced a system--already detailed in these
pages--by which the mercury is "quickened." In his method the running
water passing over the tables, or other apparatus of a similar
character, is used as the electrolyte. In this arrangement, the mercury
being the cathode, plates or wires of copper constituting anodes are
brought into contact with the water passing over the mercury in each
"riffle." Both the cathode and the anodes are, of course, maintained in
contact with the poles of a suitable source of electrical supply. The
current then passes from the copper anode through the running water
to the mercury cathode, and so on to the negative pole of the
electro-motor. As a consequence of this arrangement, hydrogen is evolved
from the water, and has the effect of reducing any oxide or other
detrimental compound of the metal; in other words, it "quickens" and
prevents "sickening" of the fluid metal, and consequent "flouring" and
loss. While the hydrogen is evolved at the cathode, oxygen enters into
combination with the copper constituting the anodes. This to some extent
impairs the conductivity of the circuit.

The latest process, however, is that of Mr. Bernard C. Molloy, M.P.,
which we have already characterized as highly scientific and effective,
the production of a suitable amalgam being obtained under the most
economical and simple conditions. This process has the advantage of
producing not only a hydrogen amalgam, but also at will an amalgam of
hydrogen combined with any metal electro-positive to this latter. Thus
hydrogen potassium or hydrogen sodium can be obtained, as will be seen
by the following description.

Mr. Molloy's effort appears to have been, in the first place, directed
to a system which could be adapted to any existing apparatus, and in
certain cases where water was scarce, to avoid altogether the use of
that, in some districts, rare commodity. For the purpose of explanation
we select an ordinary amalgamating table fitted with mercury riffles.
The surface of the table is in no way interfered with or disturbed. The
bed of the riffle, however, is constructed of some porous material, such
as leather, non-resinous wood, or cement, which serves as the diaphragm
upon which the mercury rests, and separates the fluid metal from the
electrolyte beneath. Running the full length of the table is a thin
layer of sand, supported and pressing against the diaphragm, and lying
in this sand is the anode, formed preferably of lead. A peroxide of
that metal is formed by the action of the currents, and may be readily
reduced for use over and over again after working for from one to three
months. The peroxide of lead, as is well known, is a conductor of
electricity, and this fact constitutes an important advantage in the
working of the process. The thin layer of sand is saturated with an
electrolyte, such as dilute sulphuric acid (H_{2}SO_{4} + 20H_{2}O)
to give a simple hydrogen amalgam; (Na_{2}SO_{4} + xH_{2}O) to give a
hydrogen sodium amalgam; or (K_{2}SO_{4} + xH_{2}O) to give a hydrogen
potassium amalgam. Numerous other electrolytes constituted by acids,
alkalies, and salts can be used to form an amalgam permanently
maintained in a condition of "quickness" and freed from all liability
to "sicken," whatever the components of the ore may be. The mercury
is connected with the negative pole of the voltaic battery or other
electro-motor, and the lead made with the positive pole of the same
source. When the current passes there is formed according to the nature
of the electrolyte, a hydrogen amalgam, or an amalgam of hydrogen with a
metal electro-positive to hydrogen. The electrolyte, which, it will be
understood, is distinct and apart from the body of water passing over
the table, will last almost indefinitely, there being no consumption of
any of its constituents, excepting hydrogen and oxygen from the water
of solution. The quantity of acid or saline material contained in the
electrolyte is so very small that there can be no difficulty in finding
a supply in any district. The question of the supply of electricity is
one which in many mining districts involves considerations of practical
importance, since a large supply would necessitate water or steam power.
It has been found that two cells having an electromotive force of about
two volts each will in this process suffice; if preferred, however,
a very small dynamo machine can be used. In connection with the
electro-motive force it is requisite to use, it may be observed that an
amalgam of sodium containing only a small quantity of this metal would,
when constituting a positive element in conjunction with a lead negative
and on an aqueous electrolyte, give an opposing electro-motive force of
less than three volts. Such an amalgam could therefore be obtained under
an electro-motive force of about four volts. The electrical resistance
in the circuit constituted by the apparatus being very small, no
electrical power is wasted. When water constitutes the electrolyte, as
in Barker's system, then the electro-motive force required to obtain a
given current would be very much greater than that above specified.
The conditions assured under this process appear to be all that can
be required, while the amalgams obtained are those most calculated to
preserve the "quickness" and prevent the "sickening" of the mercury.

Mr. Molloy has designed a special form of amalgamating machine to be
used in conjunction with the above process, and with or without the aid
of water. By the employment of this machine, each particle of the ore
is slowly rolled in the quickened mercury for from fifteen to thirty or
more seconds.

When the extent of the gold and silver mining industries is considered,
and when it is borne in mind that a considerable percentage of the
precious metal present in the ore is, in the ordinary process of
extraction, lost through defective amalgamation--due to insufficient
contact with the mercury or to a total absence of contact, as in the
case of float gold--it is obvious that the introduction of any system
obviating such loss is a matter of very great importance to those who
are interested in the above mentioned industries. We expect shortly to
hear of the practical introduction on a large scale of Mr. Molloy's
process, and we look forward with interest to the results which may be
obtained from it.--_The Engineer_.

* * * * *

TREATMENT OF ORES BY ELECTROLYSIS.

By M. KILIANI.

The author lays down general principles for electrolytic metallurgy.
Ores must be distinguished as good and bad conductors; the former
may serve directly as anodes, and are easily oxidized by the
electro-negative radicals formed at their contact, and dissolve readily
in the electrolyte. The bad conductors have to be placed in contact
with a conducting anode, formed of an inoxidizable substance, such as
platinum, manganese peroxide, or coke. In laboratory experiments a good
conducting ore is electrolyzed by suspension from a platinum wire in
connection with the source of electricity, and is then immersed in the
bath. On an industrial scale the ore, coarsely broken up, is placed in
one of the compartments of a trough divided by a diaphragm.

On the fragments of the ore which extend up outside of the electrolytic
bath is laid a plate of copper connected with the positive wire. Care
must be taken that this plate does not plunge into the bath, otherwise
the current would not traverse the ore at all. The cathode is preferably
formed of the same metal which is to be obtained. The bath should
not contain organic acids. In practice the common mineral acids are
employed, or their salts, selecting by preference a salt of the metal
which is to be isolated. It is convenient to pass the current through
the greatest possible number of small decomposition troughs, taking care
that the resistance in each is not too great. With a current of one and
the same intensity we obtain in n troughs n times as much metal as in a
single one. To keep down the resistance of the circuit we employ poles
of a large surface, i.e., plenty of ore and baths which are as good
conductors as possible.

The state in which the metal is deposited at the negative pole depends
on the secondary actions undergone by the electrolyte, and especially of
the escape of gas. This is a function of the _density_, of the current,
i.e., the proportion of its intensity to the surface of the cathode. If
the density is too great there is an escape of hydrogen, and the metal
is deposited in a spongy condition. If the density of the current falls
below a certain minimum, an oxide is deposited in place of metal. The
electrolytic treatment of ores often renders it possible to separate
the different metals which may be present. These are deposited in
succession, and are sharply separated if the electromotive power is not
too great.

1. _Zinc_.--The zinciferous compounds--calamine, blende, and zinc
ash--are all poor conductors. They are first dissolved, and the salts
obtained are electrolyzed, employing anodes of coke. Blende should be
roasted before it is dissolved. The electrolytic bath should be as
concentrated as possible to avoid sponginess of the metal and an escape
of hydrogen. In a saturated solution the formation of hydrogen decreases
as the density of the current augments.

2. _Lead_.--Galena is a good conductor, and may be directly
electrolyzed. The best bath is a solution of lead nitrate. The
arborescent crystallizations extend rapidly, and must be broken from
time to time to prevent the formation of a metallic connection between
the anode and the cathode. The sulphur of the galena falls to the bottom
of the bath, and may be separated from the gangue by solution in carbon
disulphide.

3. _Copper_.--Native copper sulphide, though a good conductor, cannot
be directly electrolyzed en account of the presence of iron sulphide,
whence iron would be deposited along with the copper. The copper pyrites
are roasted, dissolved in dilute sulphuric acid, and the liquid thus
obtained is submitted to electrolysis.

* * * * *

A PEOPLE WITHOUT CONSUMPTION, AND SOME ACCOUNT OF THEIR COUNTRY--THE
CUMBERLAND TABLELAND.

By E. M. WIGHT, M.D., Chattanooga, Tenn., Late Professor of Diseases
of the Chest and State Medicine, Medical Department University of
Tennessee; Late Member of the Tennessee State Board of Health, and
ex-President of the Tennessee State Medical Society.

During the ten years that I have practiced medicine in the neighborhood
of the Cumberland Tablelands, I have often heard it said that the
people on the mountains never had consumption. Occasionally a traveling
newspaper correspondent from the North found his way down through the
Cumberlands, and wrote back filled with admiration for their grandeur,
their climate, their healthfulness, and almost invariably stated that
consumption was never known upon these mountains, excepting brought
there by some person foreign to the soil, who, if he came soon enough,
usually recovered. Similar information came to me in such a variety of
ways and number of instances, that I determined some four years ago,
when the attempt to get a State Board of Health organized was first
discussed by a few medical men of our State, that I would make an
investigation of this matter. These observations have extended over that
whole time, and have been made with great care and as much accuracy
as possible, and to my own astonishment and delight, I have become
convinced that pulmonary consumption does not exist among the people
native and resident to the Tablelands of the Cumberland Mountains.

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