13/8 The Cornell Reading-Courses 



(See 4, Fig. 20.) The six-bar thennostat is merely two three-bar ther- 

 mostats riveted together. (See i, Fig. 20.) Each of these styles is 

 very satisfactory. The wafer or disc thermostats (see 2 and 3, Fig. 20) 

 are usually made of copper and filled with a very sensitive fluid. They 

 are very susceptible of a slight change in temperature. 



In addition to the types shown in Fig. 20, there is a four-bar thermostat 

 that is both sensitive and powerful. (See Fig. 21.) 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 connect- 

 ing rod is fastened. 



Regulator bar. — The regulator bar should be placed so that the pivot 

 casting rests squarely on the base casting, as indicated in Fig. ig, with the 

 disc, when attached, hanging directly over the exhaust in the top of the 

 heater. The disc should cover the exhaust evenly, entirely closing the 

 exhaust hole when down; otherwise some heat will be lost and the effec- 

 tiveness of the thermostat's action lessened. 



Placing the connecting rod. — The connecting rod is passed down through 

 the connecting tube and into the hole in the top of the thermostat. In 

 some incubators the connecting rod passes through the thermostat and 

 is fastened by screwing a nut to the bottom of the rod; in others, the rod 

 simply screws into the thermostat; either way is satisfactory. 



Counterpoise rod and weight. — The counterpoise weight is usually ad- 

 justed on the rod before leaving the factory and should not be moved 

 unless it has been pushed back so that it overbalances the bar, preventing 

 an easy action of the bar when lightly pressed down from the wire connect- 

 ing rod. In the latter case, the weight may be moved until the bar works 

 freely when the thumb screw on the connecting rod is loose above the bar. 



The counterpoise weight should never be moved to regulate the heat. 



The heater. — The heater comes already attached to the incubator, and 

 no changes should be made unless it has been damaged. The heater 

 should be gas-tight, fireproof, strong, and constructed of a material that 

 will hold all the heat given off by the lamp, thereby making it necessary 

 to run only an ordinary flame, with an economical use of oil. The heater 

 should be cleaned very carefully and thoroughly, especially if the lamp 

 has smoked. A wire with a cloth fastened to one end should be used 

 and the cleaning done by inserting the cloth into the opening and twisting it 

 until all the soot is removed. The isinglass should be cleaned thoroughly 

 after the soot is removed, otherwise it will be difficult to see the flame. 

 An oily cloth should never be used in cleaning incubator heaters. In 

 case the isinglass is broken, it should be replaced in order to prevent 

 fumes from getting into the machine and to protect the flame from 

 draughts. Fig. 22 shows the different parts of the heater. 



