(*O 235 



through the tube. The effect was substantially the 

 same when the air was permitted to bubble through the 

 liquid acid and through the solution of potash. 



Thus, on the 5th of October, 1868, successive charges 

 of air were admitted through the potash and sulphuric 

 acid into the exhausted experimental tube. Prior to the 

 admission of the air the tube was optically empty ; it con- 

 tained nothing competent to scatter the light. After 

 the air had entered the tube, the conical track of the 

 electric beam was in all cases clearly revealed. This, 

 indeed, was a daily observation at the time to which I 

 now refer. 



I tried to intercept this floating matter in various 

 ways ; and on the day just mentioned, prior to sending 

 the air through the drying apparatus, I carefully per- 

 mitted it to pass over the tip of a spirit-lamp flame. 

 The floating matter no longer appeared, having been 

 burnt up by the flame. It was, therefore, organic matter. 

 When the air was sent too rapidly through the flame, a 

 fine blue cloud was found in the experimental tube. 

 This was the smoke of the organic particles. I was by 

 no means prepared for this result ; for I had thought, 

 with the rest of the world, that the dust of our air was, 

 in great part, inorganic and non-combustible. 



Mr. Valentin had the kindness to procure for me a 

 small gas-furnace, containing a platinum tube, which 

 could be heated to vivid redness. The tube also con- 

 tained a roll of platinum gauze, which, while it per- 

 mitted the air to pass through it, insured the practical 

 contact of the dust with the incandescent metal. The 

 air of the laboratory was permitted to enter the experi- 

 mental tube, sometimes through the cold, and some- 

 times through the heated tube of platinum. * The rapid- 



