606 



Popular Science Monthly 



A New Type of Acid-Proof Brush for 

 Soldering Flux 



THE use of non-corroding paste in 

 soldering has, in many cases, done 

 away with the disagree- 

 able and dangerous acid 

 brush. There are still a 

 few jobs, however, which 

 require an acid flux for 

 soldering. To those who 

 have occasion to use sol- 

 dering acid of any kind, 

 the non - corrosive acid 

 brushes shown in the il- 

 lustration should prove 

 serviceable. 



Both of the brushes 

 shown employ a small 

 piece of rubber sponge 

 for the brush proper, 

 while the handles are 

 made as illustrated, one 

 from an old rubber pen 

 barrel and the other from 

 a section of tubular porcelain insulator. 



The piece of sponge mentioned is forced 

 into one end of the rubber or porcelain 

 handle, as shown. — R. U. Clark. 



A discarded fountain pen case 

 and a section of tubular por- 

 celain insulator for brush handles 



good insulation from the motor shaft with 

 extreme lightness. 



To make an arm embodying these fea- 

 tures, proceed as follows: From a piece 

 of fiber or bakelite of suitable length and }4 

 in. thick, cut a strip to 

 the shape shown at A. 

 The widest part should 

 equal the diameter of the 

 shaft-bushing, so as to fit 

 flush. The dimensions 

 will, of course, vary with 

 the size of your ring; but 

 in any event the length of 

 this piece should be }/i in. 

 less than the distance be- 

 tween faces of opposite 

 studs. Holes B and C 

 are for fastening to the 

 hub on the motor-shaft. 

 Holes D and E, tap 2-56, 

 are for screwing on the 

 aluminum strip shown at 



a point 



Construction of a Rotating Arm 

 for a Rotary Gap 



TO those amateurs employing a rotary 

 spark-gap of the type having the 

 studs arranged in a ring about a revolving 



F. This piece is 1% in. 

 longer than the fiber. At 

 from each end bend the 

 aluminum at right angles. This forms the 

 sparking surface. Now, about }4 i n - W 

 from the bend on both ends, curve the 

 strip as at G. Screw it down, as shown, 

 to the fiber arm. After screwing on the 

 hub, mount it as shown at H. 



The proper adjustment of distance be- 

 tween electrodes is accomplished by chang- 

 ing the stationary studs. This type of 

 rotating arm is not only extremely light, 

 allowing a quick start, but also has the 

 advantage of cooling rapidly, owing to 

 the exposed surface curving away from 

 the fiber strip. This curve should be at 

 least 1 in. from the center for good 

 insulation. 



,HUB & SHAFT 



A light rotating arm constructed so that it 

 is well insulated from the motor shaft 



arm, the construction of this arm often 

 presents difficulty; for it must combine 



Using Resistance in Field Wiring on 

 an Automobile Dynamo 



MANY times the car owner is not en- 

 tirely familiarwith the lighting system 

 and does the wrong thing when trouble 

 occurs. Cars are equipped with a gener- 

 ator that will carry about six 12 c. p., 8-volt, 

 tungsten filament bulbs. Each bulb takes 

 about 1 x /l amperes. If it is desired to use 

 only a part of the bulbs at a time it is 

 necessary to connect in the line a resistance 

 equal to that used by the bulbs cut out 

 of the circuit. This resistance should be 

 put in the shunt field wiring to prevent 

 the voltage from running too high. 



