815 
ps 
back to the end of the cable, and the unit now appears to be fixed ‘to the 
apex of a wax cone, with the base of this cone moulded to the catile end. 
The wax is reheated to 130°C and the unit dipped to give a smooth finished 
surface thereby finally leaving also a very thin wax film on the orystals, 
9. The gauge is lightly washed in petrol, and approximately 1" of the 
outer rubber covering of the cable measured from the base of the wax cone, 
is also thoroughly cleaned with petrol or benzene prior to rubberising. 
The resistance of the gauge and cable is rechecked. The gauge and cable 
end is now dipped in 60% concentrated natural latex (North British Rubber Co.) 
and rotated by hand in order to obtain a uniform thickness. The rubber 
covering is allowed to dry until it changes from the milky white to the 
transparent state. The next step is to apply a ridge of latex to the sharp 
edge of the crystal faces to counteract the dilation of the rubber due to 
surface tension. When the ridge is dry this alternate process is repeated 
three times. It is important that each coat be allowed to dry before the 
next is added; failure to observe this condition may result in a gauge of 
low resistance. The gauge and about 6" of cable enters the oven through 
a modified vent=hole, and the rubber is cured by baking at a constant 
temperature of 47°C for a minimum period of 15 hours. 
The total time taken for the construotion and attachment to the cable 
of a miniature piezo-electric gauge is approximately 36 hours. 
410. A photograph of the jig details is shown in Plate 14, and of the 
gauge before application of the special wax and natural latex, and after 
completion in Plate 15. 
