64 PROCEEDINGS OF THE AMERICAN ACADExMY 



periment irreproachable, with reference to the determination of carbon 

 in the hydrogen, we should have been obliged to extend indefinitely 

 our absorbing apparatus, and to force the air through the whole 

 apparatus, instead of sucking it through, as in the experiments above 

 described. The object in view was not worth such trouble and 

 expense, and we moreover had not the necessary appliances, so that 

 we were reluctantly foi'ced to give up the inquiry. 



Our interest in the subject has been awakened anew by some ex- 

 periments recently published by H. Karsten,* upon the oxidation of 

 dry non-nitrogenous organic substances by the action of atmospheric 

 air at ordinary temperatures. The method upon which Karsten 

 chiefly relied in these experiments was, in its essential features, iden- 

 tical with the one employed by ourselves, but the difficulty, to which 

 we have referred, of removing carbonic acid from the air employed 

 by any common absorption apparatus, is altogether ignored by him ; f 

 as will appear from the following description of his apparatus, quoted 

 from page 349 of his article : " In order to purify from carbonic 

 acid and water the air which I allowed to flow in a slow, continuous 

 stream over the organic substances, I placed before the vessel which 

 contained them chloride of calcium tubes several feet in length, and in 

 front of these a tube containing dry caustic potash, preceded by a bulb- 

 tube filled with concentrated solution of caustic potash ; by this solu- 

 tion the air was first washed and freed from carbonic acid ; it was then 

 led slowly over the dry caustic potash and through the long chloride 

 of calcium tubes, before it came in contact with the organic substances, 

 which had been dried in tlie water-bath." It is evident, at all events, 

 that this apparatus was far less adequate than our own for the difficult 

 operation of removing carbonic acid from the air. 



We do not in the least seek to deny the truth of Karsten's assertion, 

 that carbonic acid is really formed by the action of air at oi'dinary 

 temperatures upon the substances in question. The fact is not only 

 probable a pinori, but would seem to be proved by his incidental 

 statement (p. S-iS), that carbonic acid was formed when these com- 

 pounds (sugar, cork, &c.) were exposed during some months to the 

 action of air or oxygen in tubes sealed with mercury in the pneu- 



* Poggendorff's Ann. der Phys. u. Ch , 1860, CIX. 346. 



t The reader of Karsten's memoir will observe that, like ourselves, he obtained 

 for the most part only crystalline carbonate of lime, — no immediate cloudiness. 



