EMISSION HISTOSPECTROSCOPY 



111 



conditions conceivable in which the needle electrode assembly 

 might have advantages. In any case the Scott and Williams appara- 

 tus has a nmnber of significant improvements, as will be apparent 

 from the following description of it. 



The spark generator construction is shown diagrammatically in 

 Figure 6. Oscillations are produced in the primary circuit by a 

 spark passing between two thick brass discs rotated by a small 

 motor to prevent erosion and local heating. The space between the 

 discs is supplied with photoelectrons by focusing ultraviolet radia- 

 tion on it from a quartz mercury lamp. The analyzer spark in the 

 secondary circuit has an improved continuity and steadiness as a 



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Fig. 6. Wiring diagram of spark 

 generator assembly. The ionizing beam 

 of ultraviolet radiation is shown 

 focused between the rotating discs of 

 the spark gap. From Scott and Wil- 

 liams (1935) 



Fig. 7. View of box enclosing ana- 

 lyzer spark gap and electrode screen. 

 Portion of spectrograph seen at right. 

 From Scott and Williams (1935) 



result. A large open type oscillation transformer is employed having 

 two heavy primary, and twenty smaller secondary, turns wound 

 on a wooden frame as close to the edge of a 36 in. square as possible. 

 A clearance of 0.5 in. allowed between the secondary turns. The 

 condenser is composed of a stack of glass plates (8 X 8 X % in.) 

 separating eight sheets of aluminum foil (6 X 6 in.) connected alter- 

 nately. The current passing over the analyzer spark gap is about 

 0.45 ampere. 



The electrodes of the analyzer spark gap are steel balls (0.25 in. 

 diameter) placed 1.4 cm. apart which are supported through the 

 bakelite back of a metal box housing fitted with quartz and glass 



