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. After all the gas comes off you will find in
the bottom of the test tube a chunk of dry, porous coke. These, then,
are the two main products of the destructive distillation of coal. But
if you are an unusually observant person, that is, if you are a born
chemist with an eye to by-products, you will notice along in the middle
of the tube where it is neither too hot nor too cold some dirty drops of
water and some black sticky stuff. If you are just an ordinary person,
you won't pay any attention to this because there is only a little of it