g them.

The most suitable material in most cases is steel boiler plate 3/8
or 1/2 in. thick, which can be made with welded joints and will
last well.

The sizes of the boxes employed depend to a great extent on the
nature of the work being done, but care should be exercised to
avoid putting too much in one box, as smaller ones permit the heat
to penetrate more quickly, and one test piece is sufficient to
give a good indication of what has taken place. If it should be
necessary to use larger boxes it is advisable to put in three or four
test pieces in different positions to ascertain if the penetration
of carbon has been satisfactory in all parts of the box, as it
is quite possible that the temperature of the muffle is not the
same at all points, and a record shown by one test piece would
not then be applicable to all the parts contained in the box. It
has been found that the rate of carbon penetration increases with
the gas pressure around the articles being carburized, and it is
therefore necessary to be careful in sealing up the boxes after
packing. When the articles are placed within and each entirely
surrounded by compound so that the compound reaches to within 1
in. of the top of the box a layer of clay should be run around the
inside of the box on top of the compound. The lid, which should
be a good fit in the box, is then to be pressed on top of this,
and another layer of clay run just below the rim of the box on
top of the cover.

A SATISFACTORY LUTING MIXTURE

A mixture of fireclay and sand will be found very satisfactory
for closing up the boxes, and by observing the appearance of the
work when taken out we can gage the suitability of the methods
employed, for unless the boxes are carefully sealed the work is
generally covered with dark scales, while if properly done the
articles will be of a light gray.

By observing the above recommendations reliable results can be obtained,
and we can expect uniform results after quenching.

GAS CONSUMPTION FOR CARBURIZING

Although the advantages offered by the gas-fired furnace for carburizing
have been generally recognized in the past from points of view as
close temperature regulation, decreased attendance, and greater
convenience, very little information has been published regarding
the consumption of gas for this process. It has therefore been a
matter of great difficulty to obtain authentic information upon
this point, either from makers or users of such