so as to give the proportions desired for any crop. We have then the
possibility of getting the three essential plant foods altogether in
one compound with the elimination of most of the extraneous elements
such as lime and magnesia, chlorids and sulfates.
For the last three hundred years the American people have been living on
the unearned increment of the unoccupied land. But now that all our land
has been staked out in homesteads and we cannot turn to new soil when we
have used up the old, we must learn, as the older races have learned,
how to keep up the supply of plant food. Only in this way can our
population increase and prosper. As we have seen, the phosphate question
need not bother us and we can see our way clear toward solving the
nitrate question. We gave the Government $20,000,000 to experiment on
the production of nitrates from the air and the results will serve for
fields as well as firearms. But the question of an independent supply of
cheap potash is still unsolved.
IV
COAL-TAR COLORS
If you put a bit of soft coal into a test tube (or, if you haven't a
test tube, into a clay tobacco pipe and lute it over with clay) and heat
it you will find a gas coming out of the end of the tube that will burn
with a yellow smoky flame.
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