Temperature on the Viscosity of Gases. 201 



about o, 5 in most measurements, and so nearly uniform 

 throughout the trough that no perceptible difference could be 

 found at various points along the capillary. A thermometer 

 at S in the outer bath served to adjust the lamps so that their 

 heating should be such as to maintain a nearly constant tem- 

 perature. Automatic thermo-regulators were tried, but were 

 found in general to be quite as much of a disadvantage as 

 benefit, and were abandoned. 





XZL 





The details of the apparatus will be described, beginning 

 at the point where the gas enters. When air was used, the 

 laboratory air was drawn in through caustic potash to remove 

 the carbonic acid, and through concentrated sulphuric acid, 

 fused chloride of calcium, and anhydrous phosphoric acid 

 in the tubes H and I. When carbonic acid was used, 

 the gas was formed by the action of hydrochloric acid on 

 marble, purified by washing in water, dried, and freed 

 from hydrochloric acid by passing through tubes of pumice 

 coated with anhydrous copper sulphate. The gas was 

 then drawn through P into J by withdrawing the con- 

 centrated sulphuric acid from J into K, as about to be 

 described, and was there held for use. When a measure- 

 ment was in progress, the gas in J, being slowly and uni- 

 formly displaced by the sulphuric acid returning from K, 

 passed into and through H and I, arranged as already de- 

 scribed. The glass bottles J and K held each about 10 litres, 



