666 The Sources of the Nitrogen of our Leguminmis Crops. 
Earlier Experiments, which did not show Fixaiion 
OF Free Nitrogen. 
It has already been stated that the results and conclusions 
of Boussingault were against the supposition that plants as- 
similate the free nitrogen of the atmosphere. His numerous 
experiments on the subject were commenced in 1837, and were 
continued at intervals up to 1858. In all cases the substances 
he used as soil were sterilised ; in some the supplied air was 
washed ; whilst in others the plants grew in limited air, or 
were more or less protected. He experimented with a great 
variety of plants — wheat and oats representing Graminea; ; 
clover, peas, haricots, and lupins as Leguminosa: ; also garden 
cress and sunflower. 
In some of his earlier experiments, conducted in free air in a 
summer-house, tlie leguminous plants, trefoil and peas, did in- 
dicate some gain of nitrogen ; but in all the subsequent experi- 
ments there was generally either a slight loss, or, if a gain, it 
was represented by only fractions, or low units, of milligrams ; 
the larger amounts being with Leguminosas, in free air, under a 
glazed case. After twenty years of varied and laborious investiga- 
tion, M. Boussingault concluded that plants have not the power of 
assimilating the free nitrogen of the atmosphere. 
Experiments on the subject were commenced at Rothamsted 
in 1857, they were continued for several years, and the late Dr. 
Pugh took a prominent part in the inquiry. 
The soils used were ignited, washed, and re-ignited pumice 
or soil. The specially-made pots were ignited before use, and 
cooled over sulphuric acid under cover. Each pot, with its plants, 
was enclosed under a glass shade, which rested in the groove of a 
specially-made hard-baked glazed stoneware lute-vessel, mercury 
being the luting material. Under the shade, through the 
mercury, passed one tube for the admission of air, another for 
its exit, and another for the supply of water or solutions to the 
soil ; and there was an outlet at the bottom of the lute-v6ssel for 
the escape of the condensed water into a bottle affixed for that 
purpose, from which it could be removed and returned to the 
soil at pleasure. 
A stream of water being allowed to flow from a tank into a 
large stoneware Woulff s bottle, of more than 20 gallons capacity, 
air passed from it by a tube through two small glass WoulfTs 
bottles containing sulphuric acid, then through a long tube filled 
with fragments of pumice saturated with sulphuric acid, a'nd 
lastly through a AVoulff's bottle containing a saturated solution 
of ignited carbonate of soda ; and, after being so washed, the air 
