O^'LAHOMA ACADEMY OF SCIENCE 139 



arc rectifier enjoyed quite a popularity commercially but in recent 

 year- it has for the most part been replaced by the motor-generator. 

 Recent experiments, however, show that the mercury arc is particul- 

 arly fitted for high-tension rectification, and here in turn the large 

 currbersome and expensive rotary converters may be replaced by 

 tlie light and comparatively inexpensive arc rectifiers. This very 

 thing, is being done today successfully on some of the Swiss and 

 German electric railways. 



The use of the tungar rectifier in the laboratory is also limited 

 since it operates best at sma.l currents ; it can be made to operate 

 on a few milliamperes. The prevailing type that is being put on the 

 market makes use of only one half of the cycle; this pulsating 

 effect makes the current h,ard to measure with direct current instru- 

 ments unless considerable reactance is put into the circuit. This, 

 of course, cuts down the out-put. A type that would deliver suf- 

 ficient current smoothed out with a reactance so that the currenr 

 could be read with a fair degree of accuracy would cost approxi- 

 mately as rruch as a motor-generator. For simplic'ty of operation, 

 however, it is almost ideal and it is particularly suitaVe for charg- 

 ing secondary batteries. In the laboratory it can be used for small 

 currents, and for larger currents when the pulsating effect is no: 

 objectionable. The fact that it is a lamp .'pocket device, compara- 

 tively lieht and portab'e, one that can be hooked up anywhere, and 

 one that is free from any care v/hen not in use, is one not to be 

 over-looked. 



The romrron comm.ercial electrolytic rectifier, although requir- 

 ing considerable care and attention, uses both pulsations. W'th 

 Eon-e reactance in the circuit it gives a farily constant current, the 

 pulsating- effect being almost negligible except for currents near 

 eipht or ten amperes. On account of its wider steady-current range 

 suitable for laboratory use, and especially on acrount of its cheao- 

 ness, it ■'.s recommended for use in the small high school. While 

 it is not as convenient to move about as the Tungar, it is neverthe- 

 -less portable and can be m.oved from laboratory to lecture room 

 as occasion demands. 



For the larger high school the motor-generator is much more 

 desirable. Although it is not portable the connecting wires can be 

 led to any desired point. The current produced is practically con- 

 stant since it i.s subject only to the slight fluctuations of the A. C. 

 voltaee. 



The question then resolves itself into one of expense. If an 

 amount from $303.00 to $50000 is avai'able, install a motor-genera- 

 tor set; if little or nothing is available, invest a dollar cr tvvo in 

 material and construct an electrolytic rectifier. 



