32 HOW CROPS FEED. 
tus employed by Lawes, Gilbert, and Pugh, in their experiments made in 
the year 1858. 
A, fig. 5, represents a stone-ware bottle 18 inches in diameter and 24 
inches high. 
B, C, and &, are glass 3-necked bottles of about 1 quart capacity. 
F isa 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 series of 16, supplied them with water, from a reser- 
voir not shown, through the tube with stop-cock a b. 
edeis a leaden exit-tube for air. At c it widens, until it enters the 
vessel A, and another bent tube, g 8, 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 de, 
The bottles B C are partly filled with strong sulphuric acid. 
The tube D D, 1 inch wide and 3 fect long, is filled with fragments of 
pumice-stone saturated with sulphuric acid. At f/f indentations are made 
to prevent the acid from draining against the corks with which the tube 
is stopped. 
The bottle # contains a saturated solution of pure carbonate of soda. 
g his a bent and caoutchouc-jointed glass tube connecting the interior 
of the bottle # with that of the glass shade & 
ik, better indicated in 2, is the exit-tube for air, connecting the 
interior of the shade # with an cight-bulbed apparatus, ©, containing 
sulphuric acid. 
ww 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, gh, uv, and ik, 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, 7 0, passes air-tight 
through the bottom of the stone-ware vessel, and thus communicates 
with its interior. 
The tubes « v and i & 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 uw v was to supply them with water. 
The water which exhaled from the foliage and gathered on the inside 
of the shade ran off through zo into the bottle O. This water was re- 
turned to the pots through w v. 
The renewed supply of pure air was kept up through the bottles and 
tube A, B, C, D, # On opening the cock a 6, A, water enters A, and 
its pressure forces air through the bottles and tube into the shade F, 
whence it finds its exit through the tube i X, and the bulb-apparatus I. 
In its paseage through the strong sulphuric acid of B, C, and D, the air 
is completely freed from ammonia, while the carbonate of soda of Z re- 
moves any traces of nitric acid. The sulphuric acid of the bulb M puri- 
fies the small amount of air that might sometimes enter the shade 
through the tube ¢ #, owing to cooling of the air in ¥, when the current 
