METHODS AND APPARATl S. 



33 



Copper-constantan couples are used, as previously. The slide wire C-D has 

 a resistance of 0.372 ohm, and is divided into 400 divisions, each of which 

 represents 0.02 C. temperature difference; M has a value of about 1200 

 ohms; and R, about 400 ohms. The maximum resistance of V is about 100 

 ohms; this should be variable in steps of about 1 ohm each. The value of 

 W has not been measured, this resistance having been adjusted by trial. 

 0,as before, is 10,000 ohms. For B a dry cell is used, from which a measuring 

 current of about 0.00086 ampere is drawn; N is the Weston Standard cell used 



Fig. 8. Detachable thermometer lor use inside the calorimeter, with connections. A and E are of 



constantan; B and F of copper. 



previously. The potentiometer C-D consists of a 0.6 millimeter manganin 

 wire, arranged in the form of a circle, the sliding contact P being operated by a 

 knob at the center. The resistances M, R, V, and O are of manganin. 



The constantan wire from the constant-temperature flask to the inside of 

 the calorimeter is 2.05 millimeters in diameter, insulated with rubber and 

 covered with a protecting braid. As will be seen in fig. 8, this wire is soldered 



