The thermostat G consists of a long glass tube bent into a flat rec- 

 tangular coil and fastened to a perforated brass plate resting on short 

 legs on the bottom of the bath. It is filled with mercury and closed 

 at one end. To the open end is sealed a device shown in detail in fig- 

 ure 2. Electric connection is made with the mercury in the thermostat 

 through the platinum wire A, figure 2, which passes through the glass 

 wall near the double seal. The low tension current which is made and 

 broken in the thermostat at B and which operates the relay R, figure 1, 

 is taken as a shunt from the 110-volt direct-lighting current by con- 

 necting the low-tension circuit across adjacent taps on the 1,000-ohm 

 resistance coil H. There are seven such taps 

 along the coil and the potential difference between 

 two adjacent ones is about 14 volts when the coil 

 is in the 110-volt circuit. The current which 

 actuates the sounder is made and broken by the 

 relay. It passes from the relay through the 

 32-candlepower lamp I, then through the electro- 

 magnets of the sounder, and back to the line, 

 using the 110-volt direct current. The sounder 

 is of the usual form, rated at 5 ohms, and heats 

 but very slightly when the current passes through 

 continuously. Except for the simple device 

 shown for supporting the rubber tube, no other 

 change in the sounder is necessary except that, if 

 desired, the edges of the lever may be beveled so 

 that the rubber tube is closed more easily. Small 

 condensers, not shown, situated in the bases of the 

 sounder and relay are used in lessening sparking 

 when the currents are opened and closed in 

 the thermostat and the relay respectively. 



If cooling water is added at a rate very slightly 

 more rapid than is necessary, the temperature is 

 controlled with great exactness. Under these 

 conditions, however, not enough cool water would 

 be supplied should the room temperature rise considerably. On the 

 other hand, if cold water is added too rapidly the bath becomes much 

 undercooled at each addition. It has been found well so to regulate 

 the supply that water is added to the bath about half the time. The 

 temperature is then controlled within 0.1 C. irrespective of changes 

 in room temperature. 

 Approved. 



JAMES WILSON, 



Secretary of Agriculture. 



FIG. 2. Detail of thermo- 

 stat. 



o 





