•27 '2 MB JOHN AITKEN ON CLEAR SPACES IN DUSTY AIR. 



chimney. The evident objection to this is, that as the gases are cooled in the 

 depositer, the draught in the chimney will be destroyed. This, however, can 

 be avoided by the use of "regenerators." The impure air would be led to a 

 cold regenerator, where it would be cooled and its impurities deposited; and 

 when purified it would be led through another chamber, where it would be heated 

 before being sent up the chimney. This arrangement would not require heat to 

 be spent in working it, as the process would be reversed, and by simply revers- 

 ing the direction of currents from time to time the heat stored up in cooling 

 would be used for heating the purified gases before being sent up the chimney. 

 This purifying process by heating and cooling would require to be done a 

 number of times, and the air sent through a succession of regenerators before it 

 could be made perfectly pure. 



