at the present time engaged in the study of just how the change from the resonance radiation (which is scattered in all directions) to the regular reflection takes place, a matter of great interest in connection with the theory of absorption and reflection. As a matter of fact, I expect it to turn out that the mercury light does not absorb the light at all, for experiments indicate that the lateral emission of the ultra-violet light is about as bright as when white paper is used to scatter the light.

Another interesting line of investigation which I have recently carried out illustrates how new discoveries may be made by the aid of ultra-violet photography. It occurred to me that the air surrounding an electric spark might possibly be rendered fluorescent by the absorption of the very short ultra-violet waves discovered by Schumann, but that the flourescence might be made up wholly of ultra-violet light and consequently invisible. I therefore photographed the region surrounding a powerful spark discharge with a quartz lens, shielded from the direct light of the spark by a circular disk. The photograph, when developed, showed a highly luminous aureole surrounding the spark and extending out in all directions to a distance of nearly 2 centimeters. It was now necessary to prove that this was not light scattered by the dust particles in the air. To do this we have only to protograph the spectrum of the aureole. If it is similar to the spectrum of the spark we are safe in attributing it to scattered light. It it differs we know that it must be fluorescence, or the genesis of waves of different wave length from any present in the light of the spark. A photograph of the region surrounding the spark was made with a quartz spectrograph, and it was at once found that the spectrum was wholly different from that of the spark; in fact, it was almost identical with that of the oxy-hydrogen flame. For the further study of the phenomenon, a piece of apparatus was devised by which the light of the spark could be more effectually shut off. A small hole was bored through a plate of aluminum fastened to the end of a short vertical brass tube. This plate formed one electrode, the spark passing between an aluminum rod lying along the axis of the tube and the underside of the plate at the point perforated by the hole.

In a perfectly dark room, if the eye was held a little below the plane of the plate, no luminosity could be seen in the air above the hole, if it was reasonably free from dust, yet a photograph taken with a quartz lens showed a bright beam, or squirt, of light issuing from the hole. A photograph of the phenomenon is here shown, and you will notice the strong resemblance which it bears to a comet (pl. 6, g). Many weeks have been spent in an attempt to determine the exact origin of this radiation, and the question has proved to be the most baffling one which I have ever attempted to solve. The work

is still in progress, and many remarkable observations have been made, each one leaving us more in the dark than before. As an illustration I may mention a circumstance discovered by Dr. Hemsalech and myself last winter in Paris. We found that if a jet of air was blown through the squirt of light, the luminosity was destroyed in the region traversed by the moving current of air, but was of undiminished intensity both above and below this region. This makes it seem as if the emanation which comes from the spark, and which causes the luminosity of the air, must act for a brief time upon the air in order to cause the luminosity. It also shows that the emanation, whatever may be its nature, is not swept aside by the air current. We have also found that other gases become luminous when subjected to the spark emanations, the spectrum in each case being different and peculiar to the gas used, electrolytic hydrogen, for example, giving a strong luminosity.

It is thus apparent that by employing this "photographic eye" of quartz many new phenomena may be brought to light which have previously hidden themselves behind the limitations of the human eye. A study of the absorption by the candle-flame of ultra-violet has also been made. In this case the light emitted by the candle falls out of the problem, for its flame emits little or no ultra-violet. I can show you a photograph of the shadow cast by a flame of this description, and you will observe that the shadow is blackest at the point where the flame is brightest, that is, at the point where the minute carbon particles, which, by their incandescence, cause the luminosity, are being set free from the hydrocarbon vapor.

There are other questions which can doubtless be investigated to advantage by means of ultra-violet photography. It is well known, for example, that the amount of ultra-violet light emitted by a body increases with the temperature. By photographing groups of stars through the quartz silver filter, and comparing the photometric intensities of the images obtained in this way with the intensities as shown on a plate made by means of yellow light, valuable data might be obtained. This method is merely an extension of one already in use at the Harvard Observatory.

WHAT ELECTROCHEMISTRY IS ACCOMPLISHING.1

By JOSEPH W. RICHARDS,

Professor of Metallurgy, Lehigh University.

My theme is to depict for you, as clearly as I may be able, the part which electrochemistry is playing in modern industrial processes. I have no exhaustive catalogue of electrochemical processes to present, nor columns of statistics of these industries; but my object will be to classify the various activities of electrochemists and to analyze the scope of the electrochemical industries.

SCOPE OF ELECTROCHEMISTRY AND ELECTROMETALLURGY.

Chemistry is the science which investigates the composition of substances and studies changes of composition and reactions of substances upon each other. As an applied science, it deals chiefly with the working over of crude natural material, and its conversion into more valuable and more useful substances.

Some common examples, to illustrate this statement, are the conversion of native sulphur into sulphuric acid, the manufacture of soda and hydrochloric acid from common salt, the conversion of phosphate rock into superphosphate fertilizer, etc. Several pages would not suffice to merely catalogue the great variety of chemical industries; immense amounts of capital are invested in them and they are some of the most fundamental industries in their relation to supplying the needs of a rapidly advancing civilization.

Metallurgy is the art of extracting metals from their ores, and of purifying or refining them to the quality required by the metalworking industries. It is a branch of applied chemistry. The metallurgical industries form a highly important part of our national resources; on them we depend for iron, steel, copper, brass, gold, silver, lead, zinc, aluminum, etc., in fact for all the supply of metals used in arts and industry.

Electrochemistry is the art of applying electrical energy to facilitating the work of the chemist. It is chemistry helped by electricity. It is the use of a new agency in accomplishing chemical operations, and it has not only succeeded in facilitating many of the most difficult

1 An address delivered at the seventeenth general meeting of the American Electrochemical Society, in Pittsburgh, Pa., May 7, 1910, President L. H. Baekeland in the chair. Reprinted by permission from the Transactions of the American Electrochemical Society, vol. 17, 1910, being the transactions of the seventeenth general meeting, at Pittsburgh, Pa., May 4-7, 1910. In the presentation of this paper Prof. Richards showed a large number of lantern slides illustrating electrochemical works in operation.

and costly of chemical reactions, but it has in many cases supplanted them by quick, simple, and direct methods; it has even, in many cases, developed new reactions and produced new materials which are not otherwise capable of being made. A few examples will illustrate these points: Caustic soda and bleaching powder are made from common salt by a series of operations, but the electrical method does this neatly and cheaply in practically one operation; lime and carbon do not react by ordinary chemical processes, but in the electric furnace they react at once to form the valuable and familiar calcium carbide; carbon stays carbon except when the intense heat of the electric furnace converts it into artificial graphite. The list of such operations is a long one, and it may be said that the chemist has become a much more highly efficient and accomplished chemist since he became an electrochemist, and he is becoming more of an electrochemist daily. Electrometallurgy applies electric energy to facilitating the solution of the problems confronting the metallurgist. Its birth is but recent, yet it has rendered invaluable service; it has made easy some of the most difficult extractions, has produced several of the metals at a small fraction of their former cost, and has put at our disposal in commercial quantities and at practicable prices metals which were formerly unknown or else mere chemical curiosities. It has, further, refined many metals to a degree of purity not previously known. The metallurgist is rapidly appreciating the possibilities of electrometallurgical methods and they already form a considerable proportion of present metallurgical practice.

Applied electrochemistry, covering in general all of the field just described, is therefore an important part of chemistry and metallurgy, and is rapidly increasing in importance. It is a new art, people are really only beginning to understand its principles and to appreciate its possibilities; it is an art pursued by the most energetic and enterprising chemists, with the assistance of the most skilled electricians. Some of its most prominent exponents are electrical engineers who have been attracted by the vast possibilities opened up by these applications of electricity. The chemists have worked with electricity like children with a new toy, or a boy with a new machine; they have had the novel experience of seeing what wonders their newly applied agency could accomplish, and it is no exaggeration to say that they have astonished the world-and themselves.

THE AGENTS OF ELECTROCHEMISTRY.

The operating agent in electrochemistry is, of course, electric energy, which may be used in three classes of apparatus, viz:

I. Electrolytic apparatus.

II. Electric arcs and discharges in gases.

III. Electric furnaces.