626 



Popular Science ^Monthly 



ductor for the magnetic lines of force, 

 the air-gap can be very short, thus el^ect- 

 ing a large saving in the magnetizing 

 current. At the same time, unipolar 

 dynamos can be very much overloaded 

 without danger of burning the insula- 

 tion, as the magnetizing coil, the only 

 piece that need be insulated, can be 

 wound with asbestos-covered wire. Con- 

 sequently, the temperature can rise as 

 high as necessary to carry a big over- 

 load for a long time, this overload being 

 limited only by 

 the capacity o f 

 the prime-mover, 

 in the case of a 

 shunt-wound gen- 

 erator. This is a 

 great advantage 

 over multipolar 

 d y n a m o s, as in 

 these, cotton-and- 

 shellac insulation 

 is so profusely 

 used, that a com- 

 paratively slight 

 overheating i s 

 sure to injure the 

 windings. 



The table on page 625 furnishes some 

 idea of the relations of size, voltage and 

 output of the most efficient types of uni- 

 polar dynamos. 



The only serious drawback of the uni- 

 polar dynamo is the low voltage that it 

 supplies, but 

 on account of 

 the simplicity 

 of the c o n- 

 struction, sev- 

 eral machines 

 c a n be con- 

 nected in se- 

 ries, or a ma- 

 chine with 

 several disks 

 can be used, 

 and then the 

 voltage deliv- 

 ered is large. 

 The uni- 



Fig. 4. Unipolar 

 dynamo with two 

 disks revolved in op- 

 posite directions 



Fig. 5. Unipolar dynamo 



with two disks revolving 



in the same direction in 



opposite magnetic fields 



polar turbo-generator presents, as a 

 whole, the most compact and efficient 

 equipment known. The turbine is econ- 

 omical, and the unipolar requires no 

 gears to be coupled to the turbine, and 

 so receives the whole turbine power. 



An. Electric Soldering Iron 



AN electric flatiron may be used 

 in making an electric soldering 

 copper by removing the coil and fit- 

 ting over it a piece of brass tubing, 1" 

 by 5''. Cut a slot in one end to receive 

 the plug contacts, and into the same end 

 fit a handle in a bushing; into the other 

 end fit a bushing holding a copper point. 

 The plug from the flatiron may also be 

 used, and can be quickly separated from 

 the soldering tool — S. Bernstein. 



A COPPER POIMT i'oiA E BPASS BUSH.U'DIA fiTHICK 



B BRASS BUSH ^'DiA 3ZTHICK r IRON HOD i'DIA 



C CO/L FROM OLD FLAT IRON G HANDLE 



D A' BRASS TUBING I VIA 



\ The coil from an old electric flatiron is used 

 in making the heating element of this elec- 

 tric soldering iron 



Storage Battery Hints 



SINCE the introduction of the electric 

 starting and lighting for automo- 

 biles, hundreds of thousands of people 

 have becomiC acquainted with storage 

 batteries, while the expansion of the field 

 of electric passenger automobiles and 

 trucks has brought thousands of storage 

 batteries to garages for charging and 

 overhauling. Charging a storage battery 

 is not the simple thing it may seem, and 

 much damage is done to batteries by 

 careless handling. A few simple instru- 

 ments, designed to remove all guesswork 

 from charging, have just been brought 

 out by a Philadelphia concern. They 

 are as follows: 



A rubber bulb-syringe for filling and 

 equalizing the acid in the batteries. 



A pocket thermometer, graduated from 

 20 to 220 degrees Fahr., especially de- 

 signed for use in batteries while charg- 

 ing. The temperature of a storage bat- 

 tery should never be permitted to rise 

 too high. 



A hydrometer syringe, containing a 

 hydrometer graduated especially for such 

 work. The sharp point of the syringe 

 is inserted in the storage cell opening, 

 and the central portion of the syringe 

 filled with the liquid. The hydrometer 

 inside the glass cylinder will indicate the 

 state of the battery: 1300 stands for fullv 

 charged; 1275 for 75%; 1250 for 50%: 

 1225 for 25% and 1200 for exhausted. 



