any of its parts at any time. It is not enough to argue that a mixture,
even if it exists, cannot be exploded unless kindled. It is necessary to
demand that a dangerous mixture can at no time be formed, even if the
machine is tampered with by an ignorant person. The perfect machine must be
so constructed that it shall be impossible at any time, under any
circumstances, to blow it up.

It must insure cool generation. Since this is a relative term, all machines
being heated somewhat during the generation of gas, this amounts to saying
that a machine must heat but little. A pound of carbide decomposed by water
develops the same amount of heat under all circumstances, but that heat
can be allowed to increase locally to a high point, or it can be equalized
by water so that no part of the material becomes heated enough to do
damage.

It must be well constructed. A good generator does not need, perhaps, to be
"built like a watch," but it should be solid, substantial and of good
material. It should be built for service, to last and not simply to sell;
anything short of this is to be avoided as unsafe and unreliable.

It must be simple. The more complicated the machine the sooner it will get
out of order. Understand your generator. Know what is inside of it and
beware of an apparatus, however attractive its exterior, whose interior is
filled with pipes and tubes, valves and diaphragms whose functions you do
not perfectly understand.

It should be capable of being cleaned and recharged and of receiving all
other necessary attention without loss of gas, both for economy's sake, and
more particularly to avoid danger of fire.