oubled when the wire
is cooled to the temperature of liquid air, and all other metals are
largely strengthened, though none other to quite the same degree.
He found that a spiral spring of fusible metal, which at ordinary
temperature was quickly drawn out into a straight wire by a weight
of one ounce, would, when cooled to -182 deg, support a weight of two
pounds, and would vibrate like a steel spring so long as it was cool.
A bell of fusible metal has a distinct metallic ring at this low
temperature; and balls of iron, tin, lead, or ivory cooled to -182
deg and dropped from a height, "in all cases have the rebound greatly
increased. The flattened surface of the lead is only one-third what it
would be at ordinary temperature." "These conditions are due solely to
the cooling, and persist only while the low temperature lasts."

If this increased strength and hardness of a contracted metal are
what one would expect on molecular principles, the decreased chemical
activity at low temperatures is no less natural-seeming, when one
reflects how generally chemical phenomena are facilitated by the
application of heat. In point of fact, it has been found that at the
temperature of liquid hydrogen practically all chemical activity
is abolished, the unruly fluorine making the only exception. The
explanation hinges on the fact that every atom, of any kind, has
power to unite with only a limited number of other atoms. When the
"affinities" of an atom are satisfied, no more atoms can enter into the
union unless some atoms already there be displaced. Such displacement
takes place constantly, under ordinary conditions of temperature,
because the vibrating atoms tend to throw themselves apart, and other
atoms may spring in to take the places just vacated--such interchange,
in fact, constituting the essence of chemical activity. But when the
temperature is reduced the heat-vibration becomes insufficient to
throw the atoms apart, hence any unions they chance to have made are
permanent, so long as the low temperature is maintained. Thus it is that
substances which attack one another eagerly at ordinary temperatures
will lie side by side, utterly inert, at the temperature of liquid air.

Under certain conditions, however, most interesting chemical experiments
have been made in which the liquefied gases, particularly oxygen, are
utilized. Thus Olzewski found that a bit of wood lighted and thrust into
liquid oxygen burns as it would in gaseous