1904] 



The Decomposition of Ammonia by Heat. 



Ill 



Measurement of Temperature. Temperature was measured by means 

 of a Callendar-Griffiths pyrometer. The disturbing effect of the 

 current of hot air passing over the projecting head of the thermometer 

 was avoided by surrounding the head with several turns of tinned 

 iron. The temperatures were read to 0*1 C. The thermometer was 

 carefully standardised with melting ice, boiling water, and boiling 

 sulphur, and we do not think that the temperature error can in any 

 case exceed 0*5 C. 



. 1. 



Thermostat. To maintain the temperature constant an Ostwald 

 pattern regulator was used, the vessel being of porcelain and con- 

 taining air. In addition to this a Fletcher gas regulator was fixed 

 on the main supply. Any variation of temperature caused by altera- 

 tion of the barometric pressure was corrected by means of a screw at the 

 bottom of the U-tube containing the mercury. It was found con- 

 venient to adjust the gas supply to give the required temperature by 

 loading the valve of the Fletcher regulator. 



Material. The cylinder of ammonia was obtained from the Standard 

 Anhydrous Ammonia Company, and was found to contain but very 

 little impurity. In one experiment about 20 litres of ammonia were 

 passed slowly through a long worm surrounded by ice and hydrochloric 



VOL. LXXIV. I 



