OF ARTS AND SCIENCES. 217 



amount from the potash solution and the soda lime, in consequence of 

 the heat set free by the absorption. The anhydride tube weighed 

 when full about 25 grams, and is shown at C. Next was a third l' 

 tube filled with glass beads and having a few drops of strong sulphuric 

 acid at the bend. This tube, D, was not weighed, but was necessary 

 in order to indicate any sucking back of the air and to prevent any 

 vapor from thus reaching the phosphoric anhydride. The double bulb 

 forming the end of the system, shown at E, was made by melting 

 together the usual inlet tubes of two gas washers like A. In this we 

 placed 50 c.c. of a standard solution of baric hydrate, and the peculiar 

 construction was necessary in order to provide against regurgitation 

 in consequence of back pressure. The solution is easily washed out 

 of the bulbs, and wdien retitrated at the end of the process gives the 

 amount of carbonic acid, if any, which escaped the other absorbents. 

 All of these tubes were united into one system by rubber connections 

 carefully lubricated both inside and out with vaseline, a soft parafline 

 which had previously been melted and heated to remove every trace 

 of moisture. 



The manipulation of this apparatus was an interesting experiment. 

 When all had been set up as shown in Plate III., the globe being 

 full of carbonic acid, the Bunsen pump was first started, and after a con- 

 stant suction (regulated by the Mariotte's flask before described) had 

 been established, we cautiously opened the cock of the balloon, which 

 connected with the potash bulb, closely watching the flow of gas. As 

 soon as this flow began to slacken, we as cautiously opened the farther 

 cock, by which air was admitted to the balloon through the line of 

 purifiers, still closely watching and regulating the flow. We then 

 noticed a striking phenomenon. As pure carbonic acid was now 

 passing into the potash bulb, the air mixing but slowly with the 

 heavy gas at the surface of contact as the level sunk in the balloon, 

 the absorption at first was complete. If the air supply from behind 

 was not sufficient, a partial vacuum formed in A, and air was drawn 

 back through the tubes in front, as indicated at once by the bubbles 

 at the bend of D; but if the supply was carefully regulated, a perfect 

 equilibrium could be maintained in the tubes beyond, and we have 

 seen the carbonic acid flow into the potash bull) fur half an hour 

 without more than a few bubbles of air passing through the sulphuric 

 acid at the bend of I) in either direction. 



After a while, however, when the great mass of the carbonic a. -id 

 has been absorbed, bubbles of air begin to pass through D, and also 

 bubble through the baryta water beyond, and soon a steady current 



