170 



A RESPIRATION CALORIMETER. 



The fall in potential is measured by an accurate voltmeter, constructed 

 by the same company, with an accuracy guaranteed to be within o. i 

 per cent. The maximum voltage that can be read on this instrument 

 is 150. The accuracy of this instrument has been frequently tested 

 by comparison with a standard Weston voltmeter. 



The electrical connections are shown diagrammatically in figure 49. 



The present arrangement consists of a loo-ohm resistance coil of 

 German-silver wire wound on a wooden frame and suspended within 

 the chamber. This coil is capable of carrying a current of i .5 amperes. 



PIG. 49. Connections for Electrical Check Experiment. An electric current from a storage bat- 

 tery is passed through the ammeter and then through a coil hung in calorimeter chamber. 

 By means of a variable resistance the strength of current can be kept constant. A voltmeter 

 gives the fall of potential. 



Connections are made with the milli-ammeter on one side and with a 

 switch connected with the storage battery on the other side. The milli- 

 ammeter is also connected with a switch. Two wires connect the volt- 

 meter with the coil inside the chamber, and thus the fall of potential as 

 the current passes through the coil is accurately measured. The current 

 from the storage battery therefore passes in series through the milli- 

 ammeter, the coil inside the chamber, and then through a variable resist- 

 ance back to the switch. By varying this resistance, the strength of 

 current passing through the coil can be adjusted with great accuracy. 

 Both electrical instruments can be read with a magnifying glass to i 



