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The Cornell Reading-Courses 



Fig. 56. — Several styles of thermostats 



regulator, and this is used because it happens to be the one at hand. How- 

 ever, the principles followed are very similar in all incubators. 



The thermostat. — 

 The thermostat is a 

 most important part 

 of an incubator. 

 The ability of an in- 

 cubator to hatch eggs 

 depends largely on 

 the sensitiveness and 

 the power of the 

 thermostat. As the 

 heat expands the 

 thermostat, the latter, if it is properly connected, pulls down on the connect- 

 ing rod that is fastened to the regulator bar by the thumbscrew, raising 

 the disk that is hooked to the end of the regulator bar over the heater, and 

 thus allowing the surplus heat to escape. As the amount of heat de- 

 creases, the thermostat contracts, allowing the disk to drop down on the 

 heater. The thermostat is usually in place when the incubator comes 

 from the factory, but if it is found loose or detached, little difficulty should 

 be found in screwing it into place. 



There are several styles of thermostats now on the market, as seen in 

 Fig. 56. This illustration shows (i) the six-bar type, (2) the double-disk 

 type, (3) the single-disk type, (4) the three-bar type. The style most com- 

 monly used is composed of three metal bars, usually a bar of steel between 

 two bars of zinc. These bars are riveted together at both ends and ex- 

 pand in the center when heated; therefore the connecting rod is passed 

 through the bars at this point and is fastened to the lowest bar (Fig. 56, 4). 

 The six-bar thermostat is merely two three-bar thermostats riveted to- 

 gether (Fig. 56, i). Both these types are very satisfactory. The disk, or 

 wafer, thermostats (Fig. 56, 2 and 3) are usually made of copper and are 

 filled with a very sensitive fluid. They are very susceptible to a slight 

 change in temperature. 



In addition to the types shown in .Fig. 56, there is a four-bar thermostat 

 that is both sensitive 

 and powerful (Fig. 57). 

 It is composed of two 

 bars of steel and two 

 bars of zinc, which are 

 riveted together in 

 such a way that the expansion is greatest at one end. To this end 

 the connecting rod is fastened. 



Fig. 57. — Four-bar thermostat 



