90 THE FLOATING-MATTER OF THE AIR. 



two containing strong turnip-infusion and hay-infu- 

 sion unneutralized, two containing the same infusions 

 slightly superneutralized by caustic potash. The al- 

 leged spontaneous development of life was not observed. 

 The tubes exhibit to this hour the clearness and colour 

 which they showed on the day they were boiled. Her- 

 metically-sealed tubes, containing the same infusions, 

 prepared on the same day, remain equally clear ; while 

 the specimens exposed to the laboratory air have fallen 

 into rottenness. 



The experiments with calcined air were also executed 

 in another form and on a larger scale. A ' propagating- 

 glass,' similar to that already described, was cemented 

 in the same way to a slab of wood througli which passed 

 twelve large test-tubes. The infusions, as before, were 

 hay, turnip, beef, and mutton. The air being removed 

 from the propagating-glass by a good air-pump, its place 

 was supplied by other air which had passed slowly 

 through a red-hot platinum tube containing a roll of 

 platinum g-auze, also heated to redness. Tested by a 

 searching beam, this calcined air was found quite free 

 from floating matter. For two months no speck invaded 

 the limpidity of the infusions exposed to it, Avhile a 

 week's exposure to the ordinary air sufficed to reduce 

 twelve similar infusions, hung on to the slab of wood 

 outside the glass, to the muddiness of putrefaction. 



§ 20. Infusions withcb^awn from Air. 



The arrangement here was the same as that adopted 

 in the first experiment with filtered air, the only dif- 

 ference being that the bell-jar, with a view to its more 

 perfect exhaustion, was smaller. It was cemented air- 

 tight to a slab of wood through which passed three 

 large test-tubes, filled to about two-thirds of their 



