214 PROCEEDINGS OF THE AMERICAN ACADEMY 



a form of Mariotte's flask,* and by this means a current is maintained 

 through the whole system, under constant pressure. 



Purifying and Drying Apparatus. 



The air entering as we have described passed first through a wash- 

 bottle of familiar construction containing a solution of potassic hydrate, 

 Sp. Gr. = 1.44, and then through a similar wash-bottle containing a 

 concentrated solution of baric hydrate ; and if the rapidity of the cur- 

 rent was not greater than two bubbles a second, this double washing 

 was found sufficient to remove the last traces of carbonic acid. Indeed, 

 as soon as the baryta water showed the least indications of cloudiness, 

 the solutions were renewed. It was not so easy to remove the last 

 traces of moisture. 



After the air had passed the washing flasks it entered a system of 

 desiccators, shown in the lower half of the plate, where in small bubbles 

 it travelled up first one tube, and then a second tube, both 5t feet long, 

 and filled with concentrated sulphuric acid previously boiled with a 

 small amount of ammonic sulphate to remove all nitrous fumes. Leav- 

 ing the second of these tubes it entered an elongated bulb four inches 

 long by two inches in diameter filled with phosphoric anhydride ; and 

 the fact that prolonged contact with sulphuric acid is not sufficient to 

 remove the last traces of moisture was shown by the circumstance that 

 after the current has passed for several days the dry white powder at 

 the opening of the bulb showed signs of deliquescence. 



Our phosphoric anhydride was prepared by burning common yellow 

 phosphorus in a large sheet iron drum, through which a current of 

 dry air was drawn with sufficient rapidity to maintain the phosphorus 

 in rapid combustion, and the bottom of the drum was made tunnel- 

 shaped so that the anhydride could be shaken down into a self-sealing 

 fruit jar as fast as it formed. As thus prepared the anhydride has a 

 slight odor, which it loses after a prolonged current of dry air has 

 been drawn through the powder ; and after our drying tubes had 

 been filled their contents were submitted to a preliminary treatment of 

 this sort, and not until long after all perceptible odor had disappeared 

 were they used in our work. We noticed that after the anhydride 

 had been used for some time it appeared more granular and lost in 

 part its hygroscopic power. In order to make sure of this point, the 

 apparatus as far as described having been in use for several weeks, we 

 connected with the first phosphoric anhydride tube a weighed tube 



* These Proceedings, vol. xxiii. p. 163. 



