XII.] PROBLEMS. 347 



purchaser) ; (2) its apparent novelty, including points which differ- 

 entiate this invention from other methods or apparatus for securing 

 similar ends; (3) its operativeness without further invention. (To be 

 valid, a patent must be new, useful and operative.) 



17. Determine the insulation resistance of a machine or line by 

 means of a voltmeter. 



18. Make a study of a Tirrell or other voltage regulator. 



19. Study the electrolytic or " pail forge " method of heating rods 

 for welding. The following solution may be used: 10 gal. water; f Ib. 

 borax; 3^ Ib, sal soda; Ib. salt. A D.C. dynamo of 200 to 300 volts 

 has one terminal connected to a submerged lead plate in the solution. 

 The other terminal is connected to the rod or to a horizontal piece of 

 copper upon which the rod rests when contact is desired. The rod 

 becomes heated when submerged, if the current flows in the proper 

 direction. 



20. Determine the torque of a machine by the electrical method of 

 McAllister, using a shunt motor as load ; see Standard Handbook and 

 McAllister's Alternating Current Motors. 



21. Investigate various methods for obtaining a neutral on a 

 3-wire D.C. system. 



22. Operate two alternators in parallel and study the conditions 

 that determine the division of the load between the two machines. 



23. Determine the characteristics of a high frequency alternator 

 and note the effect of lagging and leading currents upon the terminal 

 voltage. With condensers in parallel with the load, no field excitation 

 may be necessary. Care is necessary in this test as there is danger of 

 excessive voltage. 



24. Select and use one or more methods for determining induc- 

 tance and capacity with a fair degree of accuracy. 



25. Connect in series two electromotive forces, one alternating 

 and the other direct (or alternating of a different frequency). Meas- 

 ure the combined voltage and determine the relation between it and 

 the separate voltages. 



26. Superpose in a conductor with resistance R an alternating cur- 

 rent /! and a direct current /, (or an alternating current of different 

 frequency). Determine the relative values of the copper loss (RI* 

 and RI*) for each current alone and (#/*) for the total current, I. 

 Determine the relation between the effective values of ./, 7 t and /,. 



