302 
IOWA ACADEMY OF SCIENCE 
/} TB-mPERATUREr COA/TROL 
Pig. 11. — Apparatus for temperature control. 
Thus, in the apparatus shown in figure 11, in which the base is 
made of soft iron, and the flexible part of brass, for each de- 
gree rise in temperature for each centimeter of length, there is 
a difference in expansion of .000007 centimeters. By making the 
length of the metal between rivets to be 10 centimeters, the half 
length which forms the triangle is five centimeters, and for 400 
degrees rise in temperature, 
the brass is 6 -f .000019 x 400 x 5 = 5.038 cm. in length, and the 
iron is 5 -p .000012 x 400 x 5 = 5.024 cm. in length. This gives a 
rise of V (5.038)^ - (5.024)^ = VT14 = .375 cm. or 
3.75 mm., which is equivalent to the expansion of 50 centimeters 
of brass. The device operates on one-fourth ampere of current, 
and regulates to one degree. Its action is clearly shown in the 
diagram, figure 12. 
Fig. 12. — Diagram of apparatus installed. 
