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The gasolin furnace is preferable to the gas furnace because it makes
less noise, requires no special compressed air outfit and yields a more
intense heat. The temperature obtainable in them is sufficient to fuse
any of the foundation bodies. The muffles of gas and gasolin furnaces
need careful watching, and just as soon as the continuity of the muffle
is broken, it is absolutely necessary that a new one be inserted to prevent
"gassing" of the porcelain. The two gasolin furnaces which deserve
the most consideration are the Brophy (Fig. 116A) and the Turner (Fig.
ii6r.). One of the principal disadvantages of the gasolin furnaces is the
lack of convenient means of regulating the heat. Unless the muffle is
kept at a high temperature it is hard to fuse high-fusing porcelains, and
unless the porcelain is placed slowly into the muffle, its texture will be
afifefted.

Fig. 117.

Since the introduction of the electric furnaces the fusing of por-
celain has been much simplified. This style of furnace has the advantage
in that the heat is not a product of direct combustion and precludes any
possibility of "gassing" the porcelain. The heat is radiated from all
sides within the oven. The porcelain can be placed directly into the
muffle without previous heating. The current can be turned on gradu-
ally until enough heat units required to fire the porcelain have been
obtained. The ease and accuracy with which the heat can be controlled
is also a great advantage. The furnace is small and its operation is clean
and noiseless, and it can be conveniently used in the operating room.
The fusing of porcelain is as exacting as any step in the construc-
tion of the inlay. It is difficult to fuse porcelain definitely without some
means of measuring the heat and many otherwise good inlays are spoiled
in the furnace. Fairly accurate results may be obtained by placing a
pellet of pure gold on the slab in the muffle of the furnace, increasing
the resistance until the pellet melts, and maintaining the heat on a given
button for the desired period.

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