rain off the forgings,
and they were stacked on curved-end loops or racks and charged into
the furnace for the second or hardening heat. The temperature of
the furnace was raised in 1-1/2 hr. to 1,550 deg.F., the rods soaked
for 15 min. at this degree of heat and quenched in the same manner
as above.

They were again drained while yet warm, placed on loops and charged
into the furnace for the third or tempering heat. The temperature of
the furnace was brought to 1,100 deg.F. in 1 hr., and the rods soaked at
this degree of heat for 1 hr. They were then removed from the furnace
the same as for quenching, but were dumped onto steel platforms
instead of into the quenching oil, and allowed to cool on these
steel platforms down to the room temperature.

PICKLING THE FORGINGS

The forgings were then pickled in a hot solution of either niter
cake or sulphuric acid and water at a temperature of 170 deg.F., and
using a solution of about 25 per cent. The solution was maintained
at a constant point by taking hydrometer readings two or three
times a day, maintaining a reading of about 1.175. Sixty forked or
one hundred single rods were placed in wooden racks and immersed
in a lead-lined vat 30 by 30 by 5 ft. long. The rack was lowered
or lifted by means of an air hoist and the rods were allowed to
stay in solution from 1/2 to 1 hr., depending on the amount of
scale. The rods were then swung and lowered in the rack into running
hot water until all trace of the acid was removed.

The rod was finally subjected to Brinell test. This shows whether
or not the rod has been heat-treated to the proper hardness. If
the rods did not read between 241 and 277, they were re-treated
until the proper hardness is obtained.

CHAPTER IV

APPLICATION OF LIBERTY ENGINE MATERIALS TO THE AUTOMOTIVE INDUSTRY[1]

[Footnote 1: Paper presented at the summer meeting of the S. A.
E. at Ottawa Beach in June, 1919.]

The success of the Liberty engine program was an engineering achievement
in which the science of metallurgy played an important part. The
reasons for the use of certain materials and certain treatments
for each part are given with recommendations for their application
to the problems of automotive industry.

The most important items to be taken into consideration in the
selection of material for parts of this type are uniformity and
machineability. It has been demonstrated many times that the ordinary
grades of bessemer screw stock