448 



Popular Science Monthly 



A New Variable Condenser 



MOST experimenters find difficulty 

 in constructing \'ariiible condensers 

 such as sold on the market, in which 

 the effectiw area of the plates varies. 

 In the condenser here described, the 

 distance between the plates is varied. 



The instrument is mounted on a 

 circular base 5K ins. in diameter; A and 

 B are brass disks 2}4 ins. in diameter; 

 B is soldered to screw E and fastened to 

 the base as in the drawing. A wire from 

 E connects B with a binding-post; C 

 and C are rubber pillars upon which the 

 brass rod D is mounted. The rod is 

 threaded so that A will remain parallel 

 to B. Between the two disks, insert a 

 sheet of mica F, about .005 of an in. in 

 thickness. The capacity is varied by 

 turning the knob G. The maximum 

 capacity will be .00176 mfds. with the 

 best grade of mica. — Matt Jarosz. 



r-\. 





■7^ — r 



^K 



'B 



The Distance Between the Plates in This 

 Condenser is Variable 



The Quenched Gap 



AMOX(i (ither things the close coup- 

 L ling, and consequently the increased 

 etiicieiicy of radiation, possible with 

 this type of gap, make its use \ery 

 desirable. Unfortunately it does not 

 prove very satisf.utory for amateur use, 

 as the 60-cycle current usually sui)plie(l 

 on lighting circuits to which amateurs 

 have access, used with ordinary trans- 

 formers, often gives a very mushy note 

 to the spark. This renders it unsuitable 

 for working through static or other 

 interference. The difhcully ma\' be 

 avoidi-d to some e.xlent 1)>' using (he 

 i|Uenched ga[) in si-rie^ with a rotary 

 gap, thus raising and regulating the 

 frequency of the discharges. The 



quenched gap can al.so be u.sed with a 

 spark-coil, but the resulting note is not 

 always very satisfactory. 



With regard to the adjustment of the 

 gap, it should be noted that the plates 

 must be kept clean and air-tight. 



THE 

 one 



A Kickback Preventer 



apparatus described herein is 

 )ne of the simplest forms of kick- 

 back preventer, and will take care of all 

 high frequenc>- surges on the primary 

 leads of a wireless transformer. 



It consists of three plates of aluminum, 

 immersed in a saturated solution of 

 sodium phosphate or bi-carbonate of 

 soda. 



In the drawing is shown a method for 

 suspending the plates in a common 

 quart mason-jar. The instrument is to 

 be connected to the apparatus as shown 

 in the wiring diagram. 



Its action is not unlike that of a 

 condenser, due 

 to the thin in- 

 sulating film 

 that forms on 

 the plates when 

 current tries to 

 pass from one 

 plate to the 

 other. Any ex- 

 treme In* high 

 voltage surges 

 will puncture 

 this film and 

 thus be d i s - 

 charged to earth. 

 The fuses will 

 prevent the flow 

 of too much live current. The film is 

 replaced .lutomatically when the voltage 

 is reduced. It ma\' be noteil that two 

 small alinninuni plates immersed in the 

 aboN'e solution placed in a test tulu', will 

 form .1 good renewing condenser ol 

 fairly high capacity.— Roukkt Kicn.nkuv. 



JVoodSfnp 



^Aluminum 

 PJaks 



Method of Suspend- 

 ing the Plates in a 

 Quart Mason Jar 



Diagram of the WirinR by Which 

 Instruments are Connected 



the 



