“It is obvious, therefore, that conditions of activation must be so chosen and regulated as to oxidize the hydrocarbons rapidly and the primary carbon slowly. Such a differential oxidation is not easy to secure since the hydrocarbons involved have a very low hydrogen content, and are not much more easily oxidized than the primary carbon itself. Furthermore, most of the hydrocarbons to be removed are shut up in the interior of the granule. On the one hand, a high enough temperature must be maintained to oxidize the hydrocarbons with reasonable speed; on the other hand, too high a temperature must not be employed, else the primary carbon will be unduly consumed. The permissible range is a relatively narrow one, only about 50 to 75°. The location of the optimum activating temperature depends upon the oxidizing agent employed and upon other variables as well; for air, it has been found to lie somewhere between 350 and 450°, and for steam between 800 and 1000°. “The air activation process has the advantage of operating at a conveniently low temperature. It has the disadvantage, that local heating and an excessive consumption of primary carbon occur, so that a drop in volume activity results from that cause before the hydrocarbons have been completely eliminated. As a consequence, charcoal of the highest activity cannot be obtained by the air activation process.” The steam activation process has the disadvantage that it operates at so high a temperature that the regulation of temperature becomes difficult and other technical difficulties are introduced. It has the advantage that local heating is eliminated. The hydrocarbons can, therefore, be largely removed without a disproportionate consumption of primary carbon. This permits the production of a very active charcoal. It has the further advantage that it worked well with all kinds of charcoal. Inferior material, when treated with steam, gave charcoal nearly as good as the best steam-treated cocoanut charcoal. Because of the shortage of cocoanut, this was a very important consideration. [Illustration: FIG. 68.—Section of Raw Cocoanut Shell. Magnified 146½ diameters.] The air, steam and also carbon dioxide-steam activation processes have all been employed on a large scale by the Chemical Warfare Service for the manufacture of gas mask carbon. [Illustration: FIG. 69.—Section of Carbonized Cocoanut Charcoal. Magnified 146½ Diameters.] [Illustration: FIG. 70.—Two-Minute Charcoal not Activated. Magnified 732 Diameters.]