170 



MEASUREMENT OF PRESSURES 



gauges to a number of laboratories carrying out research programs. 

 Further improvements were carried out in a later design, which will be 

 called the Type B gauge, and was developed at the Reeves-Ely Labora- 

 tories under the direction of A. B. Arons and Clifford Frondel (38). 

 In addition to these two basic designs, a number of special-purpose 

 gauges have been evolved, some of which are described in part (C). It 

 is beyond the scope of this section to give even a reasonably complete 



Ki-H 



h 



OURMALINE CRYSTALS 



COPPER PLATED 

 ELECTRODES 



CENTRAL CONDUCTOR 



COPPER TUBING 



SECTION SIDE VIEW 



Fig. 5.10 Construction of hourglass crj^stal tourmaline gauge. 



list of gauge developments, and reference should be made to more ex- 

 haustive discussions for further information. ^^ 



A. The hourglass gauge. This gauge design is based on the use of 

 one or more circular tourmaline disks, the faces of which are chemically 

 silvered and then electrolytically copper-plated for greater strength. 

 It was found that the electrodes frequently peeled from the crystal if 

 they made contact only with the faces. To remedy this, the edges were 

 undercut to give the crystal a "waist" or hourglass appearance, which 

 gave rise to the name. Electrodes are then applied by silvering and 

 plating the entire crystal after which the metal in the undercut is 

 ground away, as shown in Fig. 5.10, thus leaving electrodes plated over 

 the edges to provide better mechanical adhesion. The crystal element 



^2 See, for example, the reports by Greenfield and Shapiro (42), and by Arons and 

 Cole (3). 



