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51 
of the quartz crystal and mica.* Before the shellac has dried, the mica is 
cemented to the pan; similarly, the crystal is attached centrally to the 
cover. The slight depression in the cover serves a dual purpose: It helps 
in aligning the crystal, and later when the gage is finally assembled, the 
wall of the depression prevents the crystal from slipping sidewise off the 
electrode; this ensures that the full area of the crystal is utilized. 
Before the wire is connected to the electrode, the copper cable is 
pushed into the brass tube farther than it will be in the completed gage, so 
that the wire emerging from it protrudes beyond the pan. A bakelite bushing 
is then slipped over this wire. The end of the wire is bared and attached 
to the electrode at the slit with a peening hammer, seo Figure 29. A tight 
friction joint results; the short length of wire in the slit becomes virtually 
a part of the electrode. Then, while the bakelite bushing is inserted into the 
brass tube, the cable is pulled back until the copper electrode lies concen- 
trically over the mica. The cover with the attached crystal is forced into 
the pan with a small C-clamp, and presure is maintained by this clamp while 
the cover is soft-soldered to the pan. During the soldering the shellac 
films remelt; thus, upon cooling, the various components are bound firmly to- 
gether. Finally, the copper cable is soldered to the brass tube. The C-clamp 
is removed only after the metal has cooled. In both soldering operations 
great care is taken to keep the surfaces clean, so that the joints will be 
impervious to water under explosion pressures. If all the work has been done 
properly, the gage is now complete and ready for testing. 
STATIC TESTING OF THE GAGE ° 
At this stage the impedance of the gage is measured. For calibra- 
tion with the microcoulometer described elsewhere in this report, the imped- 
ance should be at least 30,000 megohms. Next, to make sure that the gage is 
watertight, it is sealed in a pressure chamber and subjected to hydrostatic 
pressures up to 3000 pounds per square inch. Once more the impedance is meas- 
ured. If the latter has dropped below its pre-immersion value, then the sol- 
dered joints may be leaky. If, on the other hand, the impedance is still 
high, the gage is ready for calibration. 
SURFACE-PRESSURE MODIFICATION OF THE QUARTZ GAGE 
The housing of the quartz gage has been successfully adapted to the 
measurement of explosion pressures on the surface of an underwater structure. 
* When the crystal is subjected to a change in pressure the opposite charges developed on its two 
faces are transmitted by induction to the central electrode and the grounded cover, respectively, 
through the layers of shellac. 
