n. Here the blending is done by mixing the proper
amount of various grades of material together. After blending the
compound, it is ready to be stored in labeled containers and delivered
to the packing room.

It will be seen that by this simple system there is the least possible
loss of energy from the compound. The saving commences the moment
the cooling cart is covered and preserves the valuable dust which is
saved by the oiling and the settling basin of the blending machine.

Then, too, there is the added convenience of the packers who have
a thoroughly cleaned, dustless, and standardized product to work
with. Of course, this also tends to insure uniformity in the
case-hardening operation.

With this outfit, one man cleans and blends as much compound in
one hour as he formerly did in ten.

CHAPTER VII

HEAT TREATMENT OF STEEL

Heat treatment consists in heating and cooling metal at definite
rates in order to change its physical condition. Many objects may
be attained by correct heat treatment, but nothing much can be
expected unless the man who directs the operations knows what is
the essential difference in a piece of steel at room temperature
and at a red heat, other than the obvious fact that it is hot. The
science of metallography has been developed in the past 25 years,
and aided by precise methods of measuring temperature, has done
much to systematize the information which we possess on metallic
alloys, and steel in particular.

CRITICAL POINTS

One of the most important means of investigating the properties of
pure metals and their alloys is by an examination of their heating
and cooling curves. Such curves are constructed by taking a small
piece and observing and recording the temperature of the mass at
uniform intervals of time during a _uniform_ heating or cooling.
These observations, when plotted in the form of a curve will show
whether the temperature of the mass rises or falls uniformly.

The heat which a body absorbs serves either to raise the temperature
of the mass or change its physical condition. That portion of the
heat which results in an increase in temperature of the body is
called "sensible heat," inasmuch as such a gain in heat is apparent
to the physical senses of the observer. If heat were supplied to the
body at a uniform rate, the temperature would rise continuously,
and if the temperature were plotted against time, a smooth rising
curve would result. Or, if sensible hea