32 now CROPS feed. 



tus employed by Lawes, Gilbert, and Pugh, in their experiments made in 

 the year 1858. 



^4, tig. 5, represents a stone-ware bottle 18 inches in diameter and 24 

 inches high. 



B, 0, and U, are glass 3-necked bottles of about 1 quart capacity. 



F is a large glass shade 9 inches in diameter and 40 inches high. 



a represents the cross-section of a leaden pipe, which, passing over all 

 the vessels A of the scries of 16, supplied them with water, from a reser- 

 voir not shown, throu;;h tlie tube with stop-cocli a b. 



c d eisa leaden exit-tube for air. At c it widens, until it enters the 

 Vessel A, and another bent tube, q r s, passes through it and reaches to 

 the bottom of A, as indicated by the dotted lines. The latter opens at 

 q, and serves as a safety tube to prevent water passing into d c. 



Tiie bottles B Care partlj' filled with strong sulphuric acid. 



The tube D D,\ inch wide and 3 feet long, is filled with fragments of 

 pumice-stone saturated with sulphuric acid. At// indentations are made 

 to prevent the acid from draining against the corks with which the tube 

 is stopped. 



The bottle E contains a saturated solution of pure carbonate of soda. 



(7 7t is a bent and caoutchouc-jointed glass tube connecting the interior 

 of the bottle ^with that of the glass shade F. 



i k, better indicated in 2, is the exit-tube for air, connecting the 

 interior of the shade F with an eight-bulbed apparatus, M, containing 

 sulphuric acid. 



w w is a vessel of glazed stone-ware, containing mercury in a circular 

 groove, into which the lower edge of the shade F is dipped. These 

 glass tubes, g h, u v, and i k, 2, pass under the edge of the shade and 

 communicate with its interior, the mercury cutting off all access of ex- 

 terior air, except through the tubes. Another tube, n o, passes air-tight 

 tlirough the bottom of the stone-ware vessel, and thus communicates 

 •with its interior. 



The tubes u v and i k are seen best in 2, which is taken at right 

 angles to 1. 



The plants were sprouted and grew in pots, v, within the shades. The 

 •tube ?<■> was to supply them with water. 



The water which exhaled from the foliage and gathered on the inside 

 of the shade ran off through 7i o into the bottle 0. This water was re- 

 turned to the pots through u v. 



The renewed supply of pure air was kept up through the bottles and 

 tube A, B, C\ B, E. On opening the cock a b, A, water enters A, and 

 Its pressure forces air through the bottles and tube into the shade Fy 

 whence it finds its exit through the tube i k, and the bulb-apparatus Jf. 

 In its passage through the strong sulphuric acid of B, C, and B, the air 

 is completely freed from ammonia, while the carbonate of soda of £ re- 

 moves any traces of nitric acid. The sulphuric acid of the bulh M puri- 

 fies the small amount of air that might sometimes enter the shade 

 through the tube i h, owing to cooling of the air in F-, when the curreut 



