n, and the physician's sedative dose represent only
a few of the devices that are derived from petroleum.

=Natural Gas.=--A natural inflammable gas occurs in or near several of the
petroleum horizons. One important belt extends through western
Pennsylvania and New York, and another through northwestern Ohio and
northeastern Indiana. It is conveyed through pipe-lines and used both as
fuel and for lighting. Natural gas occurs in a great many localities,
but is used commercially only in the regions noted. It is better adapted
for making glass than any other fuel, and on this account extensive
glass-making establishments have concentrated in the natural-gas belt of
western Pennsylvania.

QUESTIONS FOR DISCUSSION

The statement is sometimes made to the effect that coal is "condensed
sunlight"; is it true, or untrue; and why?

Why are the coal areas of Europe and America also areas of various
manufactures?

A recent cartoon had for its title--"John Bull and his coal piles
(_i.e._, coaling stations) rule the world"; show why this statement
contains a great deal of truth.

What are some of the advantages of steam-vessels over sailing-vessels?

Whale oil, crude turpentine, kerosene, and gas have been used each in
turn for illuminants; what is the advantage of each over the preceding?

Describe the structure of an ordinary kerosene lamp-burner, an argand
burner, a Welsbach burner.

For what are aniline, paraffine, naphtha, and carbolic acid used?

FOR STUDY AND REFERENCE

Obtain specimens of anthracite, bituminous, and cannel coal, and coke
for comparison and study.

Obtain specimens of crude petroleum, naphtha, refined oil, aniline dye,
paraffine, and carbolic acid; note the properties of each. Throw away
the naphtha after using.

Read Mineral Resources of the United States on the foregoing subjects.

CHAPTER XIII

METALS OF THE ARTS AND SCIENCES

The development of modern civilization is directly connected with the
mining and manufacture of the useful metals. Their effect on the affairs
of mankind can be rightly understood only when they are studied in their
relations to one another, as well as to the people who used them. Next
to the discovery of the use of fire, an appreciation of the use of
metals has been the chief thing to develop the intellect of mankind.
When human beings discarded natural caves for artificially constructed
dwellings--when they began to cook their food and clothe their bo