APPARATUS 



13 



ing the four pieces together for about 7 inches, begin to bend all four 

 pieces, fastening them together as the bending continues, so that 

 finally there will be a horseshoe shape with the parallel sides about 1| 

 inches apart. One end of the horseshoe is fastened to a block of trans- 

 ite or other non-conductor, while the other end moves freely. On this 

 free end is fastened a good platinum contact, which can be bought at 

 any automobile supply store. This contact should be on a screw, so 

 that it may be adjusted. A similar contact is fastened to a post, so 

 that the two contacts are about i inch apart. Anyone familiar with 



Fig. 9. — Paraffin bath 



electricity can make the connections. Various temperatures are se- 

 cured by changing the distance between the platinum points. To pre- 

 vent sparking, there must be a condenser in the circuit leading to the 

 thermostat. A telephone condenser (0.500MF) is satisfactory. Pos- 

 sibly, some of the cheap radio condensers would do. 



Anyone can make a bath which, if carefully watched, gives excellent 

 results (Fig. '9). It is simply cut from brass, 2 or 3 mm. in thickness, 

 with three legs screwed into it. There should be brass boxes, 10 or 

 12 cm. long, to contain the paraffin. It is neither necessary nor de- 

 sirable that the boxes have covers. Boxes are easily made from square 



