APPARATUS 
13 
The third bulb, which should be capable of raising the tempera¬ 
ture 15° or 20° C., should be connected with a thermostat. An ef¬ 
ficient thermostat, capable of keeping the variation in temperature 
within about 1° can be made in a short time. Take a piece of 
soft steel f inch wide and T V inch thick, and 17 inches long; lay upon 
it three strips of aluminium of the same width and length, but only 
-fa inch thick. These four pieces are fastened together by drilling 
numerous holes, not more than fa inch in diameter and riveting with 
pieces of brass wire. After fastening 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 1J inches apart. One end of 
the horseshoe is fastened to a block of transite 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 | inch apart. Anyone familiar with electricity can make the 
connections. Various temperatures are secured by changing the 
distance between the platinum points. To prevent sparking, there 
must be a condenser in the circuit leading to the thermostat. A 
telephone condenser (0.500MF) is satisfactory. Possibly, some of the 
cheap radio condensers would do. 
A bath which, if carefully watched, gives the very best results, 
can be made by any tinner (Fig. 11). It is simply a triangular piece 
