CURRENT TOPICS.

Activation of Carbon. (F rom Proceedings of the Thirty-ninth General Meeting of the American Electra-Chewaical Society, Sep- tember 23-26, IgIg.)-In the paper presented by N. K. Chane!~ some very interesting data have been brought forward concern- ing the conditions under which charcoal acquires and retains its absorptive and adsorptive powers. Investigation into this field was mainly stimulated by the exigencies of the late war, in which, as is well known, charcoal was used as the main ingredient of the gas-mask, but the facts thus brought forth are being rapidly applied to industrial requirements. The development of a specifi- cally activated carbon is not based solely on mere improvements of the well-known forms of charcoal, but represents a new view- point as to the general nature of the coal and the conditions of the surface. In addition to the work of Chaney, that of A. B. Lamb has contributed to the elucidation of new data. The National Carbon (‘ompany operated in conjunction with the Chemical Wal-- fare Service in perfecting the gas-mask material for the United States Army.

The main results set forth in the present paper are as follows : Elementary carbon, except diamond and graphite, exhibits

one of two forms, “ active ” or “ inactive.” All primary amorphous carbon consists essentially of a stabil-

ized complex of hydrocarbons, adsorbed on a base of active carbon. The active modification is characterized by a high specific

adsorptive capacity for gases. The inactive form exhibits no specific capacity of that type. The two forms also differ in tem- perature of formation and susceptibility to chemical action. The active modification is formed whenever carbon is deposited at 10~ temperatures, either by chemical or thermal methods, in general below 6oo* C., the inactive form from similar decompositions at higher temperatures. Tl le active form is rapidly attacked by oxi- dizing agents, even slow oxidation occurring at room tempera- ture. Hydrocarbons that decompose above 700” C. do not yield active carbon; acetylene that may be cracked at a temperature of 300” C:. does yield it. In the ordinary processes of destructive distillation at relatively low temperatures, active carbon is first formed, which, by virtue of its adsorptive capacity, takes up a certain amount of the hydrocarbons in contact with and stabilizes them so that they are retained under conditions of temperature and pressure at which they would otherwise be quickly elimi- nated. For example, quantities of a hydrocarbon resembling anthracene, the boiling point of which is 360” C., have been iso-

417

418 CURRENT TOPICS. [J. F. I.

lated from cedar charcoal which had been calcined at 850” C., and chlorine substitutions of hydrocarbons may be obtained in notable quantity by passing chlorine over coconut or other char- coals which have been calcined at similar temperatures. An in- teresting corollary of these investigations is that anthracite may be regarded as a native primary carbon, since it has been shown to possess an active carbon base saturated with adsorbed hydro- carbons. Bituminous coal and ordinary coke are of the same type.

Primary carbon is essentially an adsorption complex of hydro- carbons, adsorbed by a base of active carbon with or without asso- ciated non-adsorbed hydrocarbons.

Secondary carbon is primary carbon partially or completely broken up with formation or introduction of inactive carbon by the high temperature decomposition of its hydrocarbons.

According to the theory, carbon deposited at low temperature and absolutely free from hydrocarbons should be the purest form of active carbon and require no activating process. This was con- firmed by preparing carbon at 300~ C. by transforming carbon monoxide into carbon and carbon dioxide with the aid of ferric oxide as a catalyst. This carbon proved to be very active.

The discovery of the availability of anthracite and other natural coals and of the possibility of making synthetic primary carbon from pulverized materials by the use of the usual binders saved the country from a critical shortage of materials near the close of the war. The special forms obtained were known as Dorsite (from coconut), Bachite (from anthracite), and Car- bonite (from lampblack, powdered coal, or similar material). German carbon was made by impregnating wood with metallic salts, carbonizing and then extracting with acid. This process gives but a small amount of active carbon, but leaves an extremely fine capillary mass. These observations led to the distinction be- tween “ capillary capacity ” and “ specific capacity.” The former is distinguished by large capacity at high gas concentrations and by rapid equilibrium between the adsorbent and gas-phase in either direction, the gas being removed as easily as it is adsorbed. “ Specific capacity ” is characterized by very considerable capacity at low gas concentrations and by an extremely low rate of loss during reversal of the adsorption process.

Through these researches it has been made possible to pre- pare intelligently such active carbon on the large scale from what- ever source may be the cheapest or most desirable. The unique properties of the material both as a catalyst and adsorbent sug- gest that it will find many applications in the industries.

H. L.

Earth-current Telegraphy. CAPT. L. C. CARUS-WILSON. (The Royal Engineers’ Journal, January, rgzo.)-If an electric current is sent into the earth at one point and leaves it at another, it