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required in order to separate these plates throngh a given
distance was inversely proportional to the force that was ap-
plied. It increased nearly as the inverse square of the original
distance between the plates, and as the fourth power of the
radius of the plates; and in whatever liquid he immersed his
plates, the times were proportional to those required by equal
volumes of these liquids to flow through capillary tubes.-
19 C, VIII., 60.

I

TIE DISSIPATION OF ENERGY,
In some remarks on the dissipation of energy, Lord Ray.
leigh states that the chemical bearings of this subject are
very important. A chemical transformation is impossible if
its occurrence involves the opposite of dissipation; but it is
not true that a transformation which involves dissipation
must necessarily take place; otherwise the existence of ex-
plosives, like gunpowder, would be impossible. The possi-
bility of chemical action must often depend upon the density
of the reacting substances. Thus, in the case of a mixture
of oxygen and hydrogen in proper proportions at a certain
density, the mixture may be exploded by an electric spark,
and energy be dissipated; but beyond a certain point of
rarity the explosion can not be made, as it could not then
involve any dissipation. It may probably be found that
many mixtures which show no tendency to explode under
ordinary conditions, will become explosive when sufficiently
condensed.

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THE TRANSMISSION OF MECHANICAL POWER BY MEANS OF

ELECTRICITY.
Magneto-electric machines have not yet attained that
point of perfection which permits them to be placed among
the industrial apparatus; but they at least offer a method
of producing electricity very economically. The principal
machines are those of Siemens and Halske, of the French
Society of L'Alliance, and of Gramme. The currents pro-
duced in the last-named machines are analogous to those
furnished by the galvanic battery, thus permitting its ap-
plication to all works where voltaic electricity is useful.
The Gramme, as adapted for electro-plating in the silver-
works of Christoffle, of Paris, has a height of four feet and a

length of two and a half feet, and the resulting electric current deposits eight hundred grammes of silver per hour, requiring a motive force of one horse-power. The experiments made at London by this machine give it the first rank among apparatus for producing electric light. A curious experiment was performed with one of these machines at the Exposition of Vienna. The principal magneto-electric machine being driven by an air-engine on the Lenoir system, the electricity thus produced was carried to the electro magnets of two Gramme machines of more feeble dimensions, whicb, acting as an electric motor, kept a small centrifugal pump in action. Thus the mechanical effect of the electricity was by the connecting wires carried to a great distance from the motor. The principal advantage of the transmission of force by electricity is found in the possibility of overcoming vertical spaces which are inaccessible to the cables or belts in use in manufacturing works. Bulletin Hebdomadaire, XVI., 8.

THE MICROSCOPIC

CRYSTALLIZATION ILLUSTRATED BY

PIIOTOGRAPH.

It is often very important in chemistry or in crystallography to be able to seize exactly the delicate forms of crystals, as examined by the microscope ; but the most conscientious draughtsman can not always reproduce the fineness of these crystallizations. According to Girard, many crystals can be photographed. As a preliminary, it is necessary generally to dilute the solution to different degrees, and to allow one specimen of each kind of crystal to be formed by itself. We thus acquire the faculty of choosing that degree of concentration where the crystallographic characters are most appropriate to the methods of photography, either by reason of the delicate grouping of the forms, or by their transparency to the penetration of light. The most simple method of photographing the crystals consists in the use of an ordinary microscope, the body of which is placed in a horizontal position. In a dark room upon a table near a window the microscope is placed, and the object is illuminated by a beam of light coming through the window from a heliostat without. The luminous rays pass through the thin film of water containing the crystallized salt, traverse

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the objective of the microscope, and form a magnified image upon a distant screen. At the proper moment we substitute for the screen a sensitized photographic plate, and obtain a photograph by the ordinary processes. A number of pictures should be taken of the same object, in order to choose among them that which presents the nature of the crystalline system under the best conditions. This precaution is especially necessary in certain products, where the solution gives results distinct from each other, according to the degree of saturation.-13 B, III., 171.

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EBULLITION PHENOMENA. Dr. Phipson states that water strongly acidified with hydrochloric acid, and containing a small quantity of benzol, when placed over a spirit - lamp enters into a violent ebullition every sixty seconds. After a while

After a while the boiling ceases completely, and then recommences suddenly every thirty seconds, for a considerable period. The flask still being kept over the spirit - lamp, the periods between quiescence and violent ebullition dropped to twenty, ten, and finally to eight seconds, at which intervals the phenomena continued for a considerable time.

When methyl alcohol was added to the above mixture of water, hydrochloric acid, and benzol, and the flask placed over a spirit - lamp, no ebullition at all occurred for a long period of time, and then it took place suddenly and continued. -1 A, April 23, 177.

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ON THE RELATION BETWEEN SPECIFIC GRAVITY AND MAG

NETISM OF IRON. From a number of experiments on the magnetism of iron and steel, IIoltz concludes that galvano-plastic iron receives when made to glow by a galvanic current a greater specific gravity. The molecules are brought closer together, the intervals between them become smaller, and the permanent magnetic moment is diminished by one half. On the other hand, steel bars by being heated red-hot, and tempered, acquire a smaller specific gravity, the molecules are farther from each other than before, the intervals being greater, and the magnetic moment is notably increased. Again, Wiedeman has shown that permanent magnetism is diminished by

torsion, but temporary magnetism increases by detorsion. These effects can be explained by the same relation above found between density and the magnetic force of iron. The torsion increases the density of the iron, and the magnetism must therefore diminish. By detorsion, the molecules of the magnets are separated from each other, and the magnetism itself increases. It can, then, be assumed as probable that the magnetic forces in general are functions of the spaces between the molecules, and dependent upon the dimensions of these spaces.—19 C, VIII., 15).

RELATIONS BETWEEN CHEMISTRY AND THERMOTICS. The study of the evolution of heat in chemical combinations is a new branch of science, belonging partly to physics and partly to chemistry, and the number of facts already observed is sufficiently numerous to indicate certain laws which are set forth by Berthelot. He premises that in the act of producing any chemical change, the molecules hit sharply against one another, and give off heat, just as when a hammer strikes a bar of iron. From the study of the relations between the amount of heat and the amount of work done, it is possible to establish some theorems of thermochemistry.-12 A, X., 473.

RELATIONS OF HEAT AND ELECTRICITY. In a very suggestive article of Kohlrausch on thermoelectricity, he develops the hypothesis that currents of heat and of electricity are connected together in every conductor of heat, the heat being moved by an electric current whose heat-moving force is proportional to the electro-motive force of the heat current in the same body.-12 A, X., 278.

CONTINUITY OF THE LIQUID AND GASEOUS STATES OF

MATTER.

Professor Andrews, of Belfast, at the meeting of the British Association in 1874, made a further communication on the continuity of the liquid and gaseous states of matter. As the result of some of his more recent investigations, he stated that the compressibility of sulphurous liquids, unlike that of water, diminishes as the pressure increases. A mixture of three volumes of carbonic acid and four of nitrogen was sub

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jected to a pressure of 300 atmospheres at various tempera-
tures, from 2° to 48° C., with the very important result that,
even at 2°, the carbonic acid of such a mixture could not be
liquefied under any pressure. Indeed, the “critical point” of
carbonic acid proves to be lowered many degrees when that
gas is mixed with a non-liquefiable gas, such as nitrogen.-
15 A, Aug. 29, 1874, 277.

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THE FORCES DEVELOPED BY EVAPORATION AND CONDEN

SATION.
Professor Osborne Reynolds, in a careful review of the re.
markable observations recently made by Mr. Crookes, shows
that, according to the kinetic theory of gases, whenever a
molecule of liquid is evaporated, and becomes a molecule of
gas, it must leave the liquid surface with a velocity equal to
that with which the other particles of the gas are rebounding
among themselves; that is to say, instead of being first de-
tached, it must be shot off with a velocity greater than that
of a cannon-ball, and there must be an equal reaction on the
surface of the remaining liquid ; the contrary effect takes
place in the case of condensation. Applying the necessary
mathematical formulae, he finds that, at a temperature of
60°, the evaporation of one pound of water from a surface
is sufficient to maintain a force of 65 foot-pounds for one
second, the force being proportional to the square root of
the absolute temperature. In the case of mercury the force
is only 6 foot pounds instead of 65. And again, whenever
heat is communicated from a hot solid surface to a gas, an
effect similar to that of evaporation is produced, while for
every English unit of heat communicated to steam, at a
temperature of 60°, the reaction on the surface is equivalent
to 0.38 of a pound acting for one second ; but is, for air, 0.55
of a pound.-12 A, X., 175.

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THE HEAT PRODUCED BY GALVANIC CURRENTS.
Since the galvanic effect upon metal wires, by means of
which they are made to glow, has acquired a practical im-
portance in galvano-caustics, it appears desirable to present,
in the clearest manner, the connection between the power of
the battery, the dimensions of the wire, and the resulting
phenomenon; and the first attempt at a partial solution of

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