246 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1926 
compounds has enabled chemists to determine the structural arrange- 
ment of a large proportion of them and even, in very many cases, 
to build up or synthesize the compounds themselves from simpler 
substances or even from their elements. Among such notable tri- 
umphs are the synthesis of the vegetable coloring matters, indigo 
and alizarin; the long list of coal-tar compounds, including hundreds 
of brilliant dyes and many powerful drugs; high explosives; and the 
remarkable product known as bakelite. 
Fortunately for the student, organic chemistry is characterized by 
the frequency with which the carbon compounds occur in series of 
closely related members and in groups or families exhibiting marked 
resemblances in structure and more or less alike in properties. 
Among such series, for example, are the paraffin and olefin hydro- 
carbons, and among such groups we find the cyclic hydrocarbons as 
benzene; the alcohols, ethers, and acids; the carbohydrates, like 
starch, cellulose, and the sugars; and so on. The student is assisted 
also by the frequency with which groups of carbon and associated 
atoms enter into combination as entities, called radicals, and so 
become familiar to him as structural units. Those who insist upon 
a speaking acquaintance with each of the carbon compounds are re- 
ferred to the 4,700 pages of Richter’s Lexicon, the Who’s Who of 
carbon chemistry. 
Some faint conception of the industrial importance of the carbon 
compounds may be gained by casual reference to a few of the indus- 
tries that are directly based upon them. They will be found to 
comprehend the major portion of the invested capital, the annual 
turnover, and the workers of the nation. First of all is agriculture 
with its ramifications into prepared foods, canning, and packing. 
Closely related thereto are lumbering, naval stores, paper and tex- 
tiles, and the special industries based on individual agricultural 
products as rubber and sugar. Of lesser importance, though only 
by comparison, are explosives, celluloid, artificial silk, solvents, 
dyes, and the thousands of other synthetic products of the labora- 
tory. Of supreme significance are, of course, the fuels, coal and 
coke, natural and artificial gas, and finally, petroleum, which not 
only provides light and heat and flexible power, but supplies the 
lubricants without which the wheels of industry could not turn. 
Upon the reducing power of carbon fuels are based the steel and 
other metallurgical industries, and without the energy of their com- 
bustion we should have no steam-power plants, locomotives, motor 
cars, or ocean liners. Even the internal-combustion engines of the 
ox team and the jinrikisha would be stalled. 
