THE SOUECES OF THE NITEOGEN OF VEGETATION, ETC. 477 



which there is one included in the apparatus for each separate experiment) in a direction 

 at right angles to the plan of the figure. It is connected with each vessel A by means 

 of a tube a b, in which is fixed a stopcock, to open and shut the connexion between the 

 water-supply tube a and the vessel A. 



c de, Plate XIII., is a leaden exit-tube for air. c 1 d' e', fig. 1, Plate XIV., is the corre- 

 sponding tube in the apparatus of 1858, which is enlarged at the point d and downwards 

 until it opens into the vessel A, thus allowing another, q' r' s', to pass through it and 

 down to the bottom of the vessel A, as indicated by the dotted line. This tube q' r s' is 

 a half-inch safety-tube, opening externally at q', and in the apparatus of 1858 replaces 

 the tube q r s shown in Plate XIII. 



The bottles B and C are filled to the depth of 2^ inches with sulphuric acid of 

 sp. gr. 1-85. 



The tube D D is about 3 feet long and about 1 inch in diameter, and is filled with 

 fragments of pumice saturated with sulphuric acid. At f\f, in this tube, are small 

 indentations to prevent the sulphuric acid from draining against the corks. 



The Woulfe's bottle E contains a saturated solution of ignited carbonate of soda. 



ijli is a bent and caoutchouc-jointed glass tube, connecting the interior of the 

 Woulfe's bottle E with that of the large glass shade F. 



ik, better indicated in fig. 2, Plate XIV., is the exit-tube for the air, connecting 

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

 acid. 



ww, Plate XIII., is a block of slate 12 inches square and 3J inches thick, in which is 

 a circular groove, half an inch wide and 2 inches deep, adapted to the diameter (9 inches) 

 of the glass shade F, the bottom of which rests in it. The groove is filled with quick- 

 silver, which shuts off the communication of the external air with the interior of the 

 shade. It is widened and deepened at four equidistant points, to admit of glass tubes 

 passing underneath the shade. Two of these tubes, g h and n o, are shown in Plate XIII., 

 and ffh also in fig. 1, Plate XIV., no being there replaced by n'o'. The other two 

 are at right angles to these, and are best seen in the vertical section of the shade and 

 lute, fig. 2, Plate XIV., lettered uv and ik respectively. The tube u v is for the 

 supply of water to the plant ; and the tube i k is for the exit of the air, from which 

 it passes outwards through the sulphuric acid in the eight-bulb apparatus M. This 

 vertical section of the shade and lute is at right angles to the view of them in fig. 1., 

 Plate XIV. ; and from it a judgment may be formed of that of the shade and lute of 

 Plate XIII., as well as of the corresponding tubes to those last described, in the appa- 

 ratus of 1857. 



The tube no, Plate XIII., passing from the outside, beneath the shade, and extending 

 to the surface of the mercury in the groove within the shade, is for the purpose of 

 withdrawing condensed water. In the apparatus for 1858, the arrangement for this 

 object is rather different. Thus O, fig. 1 (and fig. 2), Plate XIV., is a bottle into which 

 passes a tube n' o', opening into the bottom of the lute w' w' by means of a hole at n', 



