rimarily by affecting the the tautomeric quilibrium between two or more unequally ctive forms of the reducing agent. The more polar, the formation of which is avoured by a high hydroxyl ion concenration, will be preferentially adsorbed by he silver halide and then may reduce the atter to metallic silver by direct electron transfer or, by the inner shift of an electron, may furnish atomic hydrogen which reduces silver ion, a reaction which may conceivably De catalysed by the metallic silver nuclei. This last theory accounts satisfactorily for the low reduction potential and long induction periods of such developers as hydroquinone and p-phenylene diamine which are highly symmetrical in their polar forms and are hence less vigorously adsorbed than are developers into which an unbalancing substituent has been introduced.

Secondary or physical development may be considered as taking place through the formation of an addition compound between the complex silver ion radical and the reduced, which breaks down in the presence of silver nuclei. The process is not fundamentally different from the adsorption process outlines above.

ELECTRIC PRECIPITATION APPLIED

TO GAS STREAMS.
By H. R. HANLEY.
(Missouri School of Mines.)
January, 1926.

The smoke, dust and fume arising from metallurgical, cement, chemical and other industries, present a problem to be considered both from the standpoint of civic nuisance and from that of economic conservation.

The removal of suspended particles from gases by means of electric discharges was first suggested in 1824 by Hohlfeld, a teacher in the Thomas school at Leipzig, Germany. He found that if he electrified a wire hung in a bottle filled with smoke, the smoke cleared rapidly and a deposit formed on the sides and bottom of the bottle. About twenty-five years later this phenomenon was again called to public notice by Buitard of London. Sir Oliver Lodge brought up the subject of electric precipitation in a series of articles in 1884, 1885 and 1886. Karl Moeller, of Germany, experimented with electric precipitation of

dust and fume and obtained a patent in Germany in 1884. No commercial application was made of his method. In 1906, Dr. F. G. Cottrell, when Professor of Physical Chemistry at the University of California, had occasion to repeat the experiments of Lodge while studying the removal of acid mists in the contact H2SO, process. He became convinced of the possibilities of commercial application of electric precipitation and tests made at the Hercules Powder Works of the De Pont de Nemours Company at Pinole, California, 1906, demonstrated this fact conclusively. First commercial installation was made at the Selby San Smelting and Lead Company on Francisco Bay for the collection of H,SO, fumes from parting kettles.

The Western Precipitation Company and the International Precipitation Company were organised for the purpose of administering the patent rights of the Cottrell process in domestic and foreign fields, respectively. In 1912 certain precipitation rights in the United States not controlled by the Western Precipitation Company were offered to the Smithsonian Institution. A separate organisation was incorporated for this purpose (inasmuch as the Smithsonian Institution could not conduct business activities), and was known as the Research Corporation of New York.

The electric precipitation of solids from gas streams when applied on a commercial scale is known as the "Cottrell Process," as it is due to Dr. Cottrell that this method, although previously known, was brought to bear upon the problem.

BRIEF DESCRIPTION.

The Cottrell Process as it exists to-day consists of passing the "smoke" or other gas stream to be cleared of its solids (or liquids) between electrodes whose difference in electric potential is very great. It has been found more economic to use a rectified alternating current rather than the usual alternating current. The conditioning of the electric energy may consist of sending an A.C. current through a step-up transformer, which delivers it at a very high potential to a revolving rectifier. This rectifier in turn delivers the electric energy in the form of an intermittent direct current at approximately the same potential as it was received. The " laboratory of the Cottrell process, wherein the gases are treated, consists of a series of pipes with a wire in the centre of each, or a system of

plates in a flue with wires at suitable distance. The pipes or plates, depending upon which type is used, constitute the positive pole and the wires the negative pole. The rectified current at say 50,000 volts or more is now passed between these electrodes while the gas stream flows parallel with the length of pipe of flue whch is at right angles to the path of the electric field. The velocity of the gases is controlled to the end that there will be provided sufficient time for the precipitation action to be fully effective before these gases are discharged. The successful precipitation of the solids is accomplished providing these deposits are conductive, or by virtue of some conductive gas in the stream condensing on the surface of the particles, they are rendered superficially conductive. A gas stream containing an excess of sulphuric acid over that required to combine with the oxides affords the most desirable conditions. If there is a deficiency of SO, in the stream this compound may be introduced artificially. If this method of causing conductivity is not found economical, the stream must otherwise be conditioned, as for example, the introduction of water vapour or steam. There are many other factors of importance which are inherent in the process, such as temperature of stream, percentage of solids, character of solids, i.e., whether a fume or a physical solid is to be treated, etc. The knowledge of these factors and the proper regulation of the variables result in clearing the gas streams of the solids which may be recovered, and the valuable constituents subsequently reclaimed therefrom. The operation of the process then presents a twofold purpose, viz., the prevention of a nuisance which the dissemination of these solids might cause and the recovering of the valuable constituents present in the solids.

The discussion which follows will be principally confined to the fundamentals of the process in order to develop reasons for certain plant procedures.

charged body it is influenced by this field and receives positive and negative charges of electricity. The pith ball will move in one way or another, depending upon the polarity of the charged body. This movement occasioned by attraction or repulsion of unlike or like charges respectively takes place in an electrostatic field where the flow of electric current is practically zero.

There is more or less freedom with which these charges may be detached from the pith ball.

The laboratory of the Cottrell process is an atmosphere of intense electrification due to a great difference in potential between the electrodes. The particles of smoke, fume and dust are extremely minute relative to the size of the pith ball mentioned, and are very numerous. These particles receive charges in a different manner than do the large pith ball. The large difference in potential between the electrodes causes a corona current to flow in the field. are certain essential phenomena characteristic of this colona current which causes the charging of the particles in the gas stream. In this we are concerned with the surge of electrons emanating from the negative electrode.

There

The polarisation of the pith ball is a manifestation of the phenomena which occur in the splitting up of the atoms into their electronic components.

This analogy is helpful in getting a perspective of events occurring in the electric field; but the cause of the charge, the structure of matter, the electronic migration and ionisation agents should be given due consideration at the start.

The suspended particles in a gaseous medium when subjected to the action of intense electric field, become charged by the action of the travelling electrons and consequently tend to travel with these electronic streams.

ATOMIC STRUCTURE.

The atomic theory of matter is useful but is for the classification of elements. The concept of definite and indivisible atoms, of different weights could not be the ultimate solution of the problem of material structure. It provides no answer to a variety of problems. The difference in chemical properties between two atoms, say hydrogen and oxygen, can never be explained by the simple difference in weight. The varying valence of the different elements and also the varying valences of a single element

remain entirely unexplained on the basis of the simple atomic theory. The spectral differences among the elements are likewise unexplainable.

The similarity and periodicity of properties, both physical and chemical, is strong evidence that similar elements must possess similarities of architecture not shown by a theory of indivisible atoms.

THE ELECTRON.

Faraday's experiments on the conduction of salt solutions are the first experiments indicative of accurate units of electricity. Faraday's law may be expressed as follows:

"For every chemical bond which is ruptured within an electrolyte a certain quantity of electricity traverses the electrolyte which is the same in all cases.'

The most startling result of Faraday's law is this, if we accept the hypothesis that elementary substances are composed of atoms, we cannot avoid concluding that electricity also, positive as well as negative, is divided into definite elementary portions, which behave like atoms of electricity.

to

Faraday's law was not sufficient establish the atomic concept of electricity. It applied to solutions of electrolytes. The proof of atomic electricity did not come until mechanism of gaseous conduction had been studied and the properties of gases acted upon by X-radiation and radio active materials had become familiar. Gases treated with X-rays were found to be conducting. The conductivity thus induced in a gas was caused by an agency which could be removed by:

1. Filtration through glass wool.
2. By passage through metal tubes

or

between plates maintained at sufficiently large potential differences. The conductivity was therefore due to electrically charged particles.

More detailed knowledge of the nature of charged particles was obtained by the study of the conduction of electricity through gases at low partial pressures. When currents at high potentials are discharged through gases about 0.01 mm. or lower, charged particles or corpuscles are shot off from the cathode. These particles were first investigated by Sir William Crookes, and called by him the "fourth state of matter" (Chemical News, XLI., 275). They have properties, the sudy of which led to an appreciation of their significance in atomic structure.

The cathode particles were shown to have the following properties;

1. "They travel in straight lines normal to the cathode and cast shadows on opaque object placed in their paths.

an

2. They are capable of producing mechanical motion.

3. They produce phosphoresence in many objects exposed to their action (exampleblue phosphoresence in lead glass).

4. They produce rise in temperature in objects they strike.

5. They may be deflected, by electromagnetic and electrostatic fields from their normal rectilinear paths.

6. The charge carried by the particle is negative since they electrify negatively insulated metallic electrodes upon which they fall.

7. They may penetrate thin sheets of metal, the stopping power of the metal varying directly with the thickness of the metal and with its density.

8. They act as nuclei for condensation of supersaturated vapours. The fogs thus formed are useful as a means of rendering the particles visible.

9. The particles are identical in nature and in the ratio of charge carried to the mass of the particles, independent of the nature of the residual gas in the discharge tube, and of the electrodes used. This represented the first definite indication. that the cathode particles were a common constituent of all atoms.

Our modern theory, therefore, includes the statement that charges of electricity are. composed of the so-called electrical atoms, each one of which is made up of the same quantity of electricity. The molecules of all material substances, whether gases or liquids, when in their neutral state, obviously possess equal quantities of positive and negative electricity. There is no evidence of the existence in atoms of any particles other than these two.

To be Continued Next Week.)

Nem Patents.

These particulars of New Patents of interest to Readers have been selected from the Official Journal of Patents, and are published by special permission of the Controller of His Majesty's Stationery Office.

Latest Patent Applications. 22,655.-O. G. Farbenindustrie Akt-Ges. -Manufacture of azo-dyestuffs, September 14th.

22,56.-Ermen, W. F. A.-Manufacture

of vat dyes. September 13th .

23,003. Hayhurst, W.-Pumps for acids etc. September 17th.

23,061. Higgins, E. B.-Processes for carrying out chemical reactions at high temperatures. September

18th.

22,985.-I. G. Farbenindustrie Akt-Ges. Dyeing cellulose esters, etc. September 17th.

Specifications Published.

257,689. Blackburn, H. W., & Thomas, W. Manufacture of ammonia. Manufacture of

257,968.-Dreyfus, H.

acetic anhydride.

257,991. Soc. of Chemical Industry in Basle. Preparations of dyestuffs. 235,588.-Buchner,M.-Process of producing hydroxides and carbonates. 258,020. Mallabar, H. J. Manufacture of cellulose acetate.

Printed Copies of the full Published Specification may be obtained from the Patent Office, 25,Southampton Buildings, London, W.C.2., at the uniform price of 1s. each.

Abstract Published.

255,925.-Photographic developers.

Schestakoff, P., and Merejkovsky, B., 4, Passage Jean-Nicot, Paris. To rectify errors in exposure ordinary developing compositions have added thereto hydroxylamine sulphonic acids or nitrilosulphonic acid, or salts thereof. As an example hydroxylamine isodisulphonate of soda (5 grms.) is added to a developer comprising hydroquinone (5 grms.), sulphite of soda (20 grms.), carbonate of soda (40) grms.), bromide of potassum (1 grm.), and water (1000 grms.).

255,434. Synthetic drugs. Chemische Fabrik Auf Actien, Vorm. E. Schering, 170, Mullerstrasse, Berlin. Pyrazolone-barbituric acid compounds. Double compounds of dialkylbarbituric acids and dimethylaminophenyldimethylpyrazolone are prepared by melting the components together and cooling them, both operations being effected in an atmosphere of an inert gas, such as carbon dioxide, hydrogen, and nitrogen. By the exclusion of air, colourless products are obtained. An example is given of the preparation of the pyrazolone compound of diethylbarbituric acid in a vessel through which carbon dioxide is passed before and during the melting operations.