SPECIFIC HEAT OF AMMONIA. 337 



f. Apparatus for calibration of Standard Thermometer. 

 Instrument was calibrated at the ice, steam, and naphthalene 

 points. Shaved ice and distilled water mixed to a slush 

 and contained in a thermos bottle were used for the zero 

 point. A steam hypsometer with three outlets and a 

 manometer was used for the steam point. The head of the 

 thermometer was protected from radiation by a square flat 

 tin sliield between the head and the hypsometer. A special 

 glass tube with two side condensing tubes was used for the 

 napthalene boiling apparatus. Instrument protected by 

 the usual aluminum radiation and splash shield, and the 

 head protected as in the determination of the steam point. 



g. Apparatus for calibration of Observing Thermometer. 

 Assembled calorimeter withdrawn from the vacuum flask 

 and its enclosing brass cylinder, and screwed into the 

 "calibration tube" shown in Figure 6. This calibration 

 tube was filled with mercury. The whole apparatus was 

 then immersed in the oil bath, the observing thermometer 

 being in metallic contact with the oil through the medium of 

 the two tubes of mercury. Comparisons with the stand- 

 ard thermometer were made at tliree temperatures. 



4. Constant Temperature Bath. 



a. Tank. 



Cubical galvanized iron tank, 2 feet on a side, riveted 

 and soldered at the bottom and lagged with felt. Cover of 

 l^-inch asbestos board with central opening to admit the 

 calorimeter which was supported by arms from this cover. 

 Tank was mounted on castors to facilitate movement in 

 case of emergency. 



b. Oil. 



Steam engine cylinder oil was used for the bath but owing 

 to its viscosity at low temperatures it is not a particularly 

 desirable substance. 



c. Stirring. 



Bath was stirred by eight 9-inch propeller blades carried on 

 two vertical shafts, driven by belt from direct current 

 motor whose speed could be controlled by a rheostat. 



d. Adjusting heater. 



3600 watt heater, wound with nichrome tape on asbestos 



