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Dr. F. Ewing Roach, of Chicago, has designed
Dr. bomb's Device. a device for making models under pressure (Fig.
85), which simpHfies their construction and assists
m obtaining more accurate models The impression is invested in the
base, which is filled with moldine (Fig. 86). The cement is mixed to a
puttv-like mass and packed in the impression, then the cylinder, which is

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Fig. 85. Fig. 86.

filled with moldine, is screwed to the base and the plunger forced toward
the base by screwing it in the cylinder. This makes constant and uniform
pressure on the model while it is setting, thereby giving a sharper im-
print than can be made by packing the material into the impression with-
out constant pressure.
When the model is to be constructed of the
inlay metal or of a low fusing alloy, the impressions
Che flinhor'S
DePice. should be oiled and invested in moldine, imbedding
all except the impression of the cavity and the walls
adjacent to it. The ring of a swaging device (Fig. 87), which acts as
a matrix for the molten metal, should be placed over the impression with
its larger opening downward, and with the center of the ring over the
center of the impression. Care should be exercised to prevent the inlay
metal from becoming overheated, and in case it ignites the flame should

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