RAW QUARTZ, ITS DEFECTS AND INSPECTION 361 



in trial manufacture, to select for jirocessing stones which have the desired 

 type of defect in large (to maximum) cjuantitics per-unit-volume. Due to 

 the many variables involved in l)()th selection of material and in manu- 

 facture, a large quantity of stones must be processed for a fair trial. The 

 criterion of usability of the defective material will then be related to number 

 of usable finished plates (satisfying the required electrical and physical 

 specifications on the finished })late) that can be obtained from a given quan- 

 tity of raw quartz (and thus to the relative costs of producing satisfactory 

 finished plates from defective and from non-defective quartz). 



If and when a type of defect lias been shown to be harmful by the above 

 method, steps may then be taken to ascertain if some method of selection or 

 measurement can be made on the defective raw quartz to separate the eco- 

 nomically usable from the economically unusable material during inspection. 



