172 



MEASUREMENT OF PRESSURES 



as to permit the use of thinner crystals without the wasted area of the 

 faces resulting from undercutting. Electrodes exhibiting much greater 

 adhesion to the crystal than is provided by chemical silvering and cop- 

 per plating can be formed by baking on silver-spray solutions. It was 

 found, however, that much subsequent soldering to the electrodes set up 

 stresses and weakened the adhesion considerably, thus resulting in elec- 

 trodes which frequently loosened or otherwise made poor contact. 



CURED 

 LATEX 



EDGE SCE 



Fig. 5.11 Construction of Type B tourmaline gauge. 



Gauges constructed by simply attaching electrical leads by local solder- 

 ing were found to give unreliable and erratic results, and the Type B 

 construction was devised to prevent local stresses and minimize han- 

 dling of the electrodes. The construction is shown schematically in 

 Fig. 5.11, and consists basically in sweating two or four circular disks to 

 a central steel tab, to which a copper-tubing shielded cable (see section 

 5.8) is attached. Small leads are soldered to the other (ungrounded) 

 faces of the crystals in the sweating operation, thus eliminating the need 

 for subsequent local heating of the crystal by soldering. These leads 

 are then connected to the insulated central conductor of the copper- 

 tubing cable. The design also readily lends itself to balanced, or push- 

 pull, gauge constructions. Either 2- or 4-pile gauges with a total thick- 



