CARBON—LITTLE 247 
SOURCE OF ENERGY 
The economic position of a nation is determined in large measure 
by the supples of energy available to its people, and their social 
progress is similarly conditioned by the extent to which the price of 
energy permits its broad and general utilization and so increases 
manifold the effectiveness of the human factor in production. Cheap 
enerey, efficiently used, is the formula for high wages and low prices. 
Most of the energy upon which civilization depends to-day is 
derived from carbon and the compounds of carbon and hydrogen. 
In use, their potential energy is always first transformed into heat 
energy. The burning of 12 grams of carbon to carbon dioxide lber- 
ates 97,000 calories, and the combustion of 4 grams of hydrogen sets 
free 136,600. Since coal consists essentially of carbon with variable 
amounts of volatile hydrocarbons, while petroleum is a complex 
mixture of hydrocarbons, our reserves of coal and oil constitute vast 
reservoirs of potential energy. One pound of coal burned delivers 
heat sufficient to raise the temperature of 7 tons of water 1° F., an 
amount of energy that would lift a ton more than 1,500 feet. ‘The 
same amount of petroleum burned would develop nearly 30 per 
cent more heat. Cheap coal and abundant petroleum must, there- 
fore, be counted among the greatest material assets of a nation, and 
the United States has been bounteously supplied with both. It 
contains about 50 per cent of the world’s reserves of coal, and despite 
the long drain upon our petroleum resources, we are still supplying 
70 per cent of the world’s production. 
COAL 
All the vast quantity of coal contained in the world and the 
still more vast amount of lignite originally came from carbon 
dioxide once present in the atmosphere. Long years ago, under 
the influence of sunlight, the plants constituting the rank and exuber- 
ant vegetation of the Carboniferous Period withdrew carbon dioxide 
from the air and built the carbon into their structure just as plants 
everywhere are doing to-day. A spruce tree weighing 1,000 pounds 
when dry has derived less than 3 pounds of mineral matter from 
the soil, but it contains more than 500 pounds of carbon combined 
with oxygen and hydrogen, the elements of water. In the warmth 
and humidity of the Coal Period, when the proportion of carbon 
dioxide in the atmosphere was perhaps greater than at present, trees 
unlike living conifers, but more resembling the ginkgo, grew lux- 
uriantly with great ferns, giant club mosses, and gigantic horsetails. 
Ferns with fronds 10 to 20 feet long so deluged their surroundings 
with their spores that some coals seem to be almost wholly made of 
