ourse shut
off. That which was produced in Germany by the distillation of beech
wood was not even enough for the high explosives needed at the front. So
the Germans resorted to rotting potatoes--or rather let us say, since it
sounds better--to the cultivation of _Bacillus macerans_. This
particular bacillus converts the starch of the potato into two-thirds
alcohol and one-third acetone. But soon potatoes got too scarce to be
used up in this fashion, so the Germans turned to calcium carbide as a
source of acetone and before the war ended they had a factory capable of
manufacturing 2000 tons of methyl rubber a year. This shows the
advantage of having several strings to a bow.

The reason why acetylene is such an active and acquisitive thing the
chemist explains, or rather expresses, by picturing its structure in
this shape:

H-C[triple bond]C-H

Now the carbon atoms are holding each other's hands because they have
nothing else to do. There are no other elements around to hitch on to.
But the two carbons of acetylene readily loosen up and keeping the
connection between them by a single bond reach out in this fashion with
their two disengaged arms and grab whatever alien atoms happen to be in
the vicinity:

| |
H-C-C-H
| |

Carbon atoms belong to the quadrumani like the monkeys, so they are
peculiarly fitted to forming chains and rings. This accounts for the
variety and complexity of the carbon compounds.

So when acetylene gas mixed with other gases is passed over a catalyst,
such as a heated mass of iron ore or clay (hydrates or silicates of iron
or aluminum), it forms all sorts of curious combinations. In the
presence of steam we may get such simple compounds as acetic acid,
acetone and the like. But when three acetylene molecules join to form a
ring of six carbon atoms we get compounds of the benzene series such as
were described in the chapter on the coal-tar colors. If ammonia is
mixed with acetylene we may get rings with the nitrogen atom in place of
one of the carbons, like the pyridins and quinolins, pungent bases such
as are found in opium and tobacco. Or if hydrogen sulfide is mixed with
the acetylene we may get thiophenes, which have sulfur in the ring. So,
starting with the simple combination of two atoms of carbon with two of
hydrogen, we can get directly by this single process some of the most
complicated compounds of the organic world, as well as many others not
found in nature.

In t