CARBON—LITTLE 237 
coal became scarce by the sixteenth century, and in 1740 coke, an- 
other form of carbon, was introduced and saved the declining iron 
industry. It is curious, however, to note how long it took to make 
the simple change. In 1619 Dudley, an English ironmaster, first 
substituted coal or coke, it is not certainly known which, for char- 
coal and continued his efforts through many vicissitudes for more 
than 40 years, only to end in commercial failure. Not until Abraham 
Darby, about 1730, renewed the attempt was success achieved and 
the modern iron industry initiated. Twenty-six years later Darby 
declared his furnace to be “at the top pinnacle of prosperity, 
making 22 tons [of iron] a week.” Prosperity, like other things, 
is relative. The United States, in 1925, had an estimated produc- 
tion of over 50,000,000 tons of coke, most of which was consumed 
in smelting iron ore. 
It was between two charcoal points that Sir Humphrey Davy, in 
1821, first produced the electric arc, and carbon in denser form has 
since played a conspicuous and essential part in the development of 
the electrical industries. It still serves as the terminals in the arc 
lamp and, until displaced by the tungsten filament, was for many 
years the source of light in the incandescent lamp. Of it are com- 
posed the electrodes of batteries and of the great electric furnaces 
employed in the production of brass, aluminum, electric steel, and 
ferrous alloys. Grains of carbon form the variable resistance 
through which speech is transmitted in the telephone, and back of 
all the bewildering opulence of word and sound that comes to us 
by radio are similar grains of carbon in the microphone. In the 
photophone, which marvelously transmits speech along a beam of 
light, such refinement of delicacy was required in the contacts that 
they were made of carbonized dandelion down. 
Charcoal, by reason of its porous structure, presents an enormous 
internal area, which may, in case of specially prepared or activated 
charcoal, be as great as 20,000 square yards, or about four acres, for 
a cubic inch of the material. As a result, it exhibits in very high 
degree the phenomena of surface attraction or adsorption, by which 
it is able to condense gases and vapors within its pores or to remove 
and hold coloring matters from liquids filtered through it. It has 
consequently long been employed as a decolorizing agent and in the 
form of bone black for refining sugar, while the more intimate 
knowledge of its properties forced upon us by the exigencies of the 
war has extended its use into far more important fields. The dire 
necessity of devising means for the protection of troops against 
attack by poison gas forced the chemists of the Allies to an intensive 
study of the factors conditioning the adsorptive power of charcoal 
for use in the canisters of gas masks. It was presently determined 
