THE SOURCES OF THE NITROGEN 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 ab, in which is fixed a stopcock, to open and shut the connexion between the 
water-supply tube @ and the vessel A. 
cde, Plate XIIT., isaleaden exit-tube for air. ¢'d'é’, fig. 1, Plate XIV., is the corre- 
sponding tube in the apparatus of 1858, which is enlarged at the point c and downwards 
until it opens into the vessel A, thus allowing another, q'7’s', to pass through it and 
down to the bottom of the vessel A, as indicated -by the dotted line. This tube g'r's' is 
a half-inch safety-tube, opening externally at g', and in the apparatus of 1858 replaces 
the tube g 7 s shown in Plate XIII. 
The bottles B and C are filled to the depth of 24 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 ff, 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. 
gh 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 3+ 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, gh and no, are shown in Plate XIIL., 
and gh 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 wv and 7# respectively. The tube wv is for the 
supply of water to the plant; and the tube ¢# 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 XIIL, 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 /o', opening into the bottom of the lute w'w' by means of a hole at w’, 
