76 
SIR J. B. LxiWES AXD PROFESSOR J. H. GILBERT OX THE 
It is added that these amounts do not include the nitrogen in the stubble and roots, 
which in the case of the oats would be very little, in that of the beans and lupins not 
much, but in the sand-peas considerable, as also in the clover. It is to be observed, 
moreover, that no account of the nitrogen in the unwashed sand is here taken. But 
Wolff points out that the gain was the largest in the case of the peas grown in the 
washed sand, which showed only a trace of combined nitrogen. Again the cement 
cases and their contents were exposed to the weather from year to year whilst there 
was no crop ; but Wolff points out, as is doubtless true, that the amount of combined 
nitrogen brought down in the rain and dew would be quite immaterial. 
Admitting it to be established that plants do not assimilate the free nitrogen of the 
air, he thinks the only remaining hypothesis is that certain plants are enabled to 
appropriate the combined nitrogen of the air, either directly through their leaves, or 
by absorption in the soil; and the latter he considers by far the most probable. In 
reference to this point he refers to Lhe results of experiments made to determine the 
amount of ammonia absorbed from the air by dilute acids exposed in shallow vessels. 
In this way A. Mullee, estimated that 12 kilog. of ammonia were absorbed per 
hectare (= 10'7 lbs, per acre), per annum, in Sweden ; whilst O. Kellner’s estimate in 
Japan, was 14 kilog. per hectare (= 12‘5 lbs. per acre). O. Kellner also determined 
the amounts of nitiic and nitrous acids absorbed by solutions of potassium carbonate. 
The quantities of nitrogen so absorbed corresponded to 11‘78 kilog. per hectare as 
ammonia, and to 1'30 kilog. as nitric and nitrous acids; giving a total of 13’08 kilog. 
of nitrogen per hectare {= 11‘68 lbs. per acre), per annum. Other experimenters have, 
however, found much more. Thus, reckoning according to Schlcesing’s experiments, 
in one of wdiicli a quantity of soil gained at the rate of 2‘59 kilog. ammonia per hectare 
in 14 days, and in another 4'097 kilog. in 28 days, the amounts absorbed would be in 
the one case 68, and in the other 53 kilog. per hectare (= 60‘7 and 47'3 lbs. per acre) 
per annum. Wolff points out that even these amounts are small compared with the 
quantities of nitrogen assimilated in the experimental crops. He further remarks that 
his porous sand would probably present more than a hundred times the absorbing 
surface of an acid or alkaline solution of the same area. 
Besides ammonia absorption, he thinks there is probably another way in which a 
humus-free soil may become a source of nitrogen to plants; viz., by the combination 
of free nitrogen, under the influence of calcium carbonate. He quotes B. Frank 
Landw. Presse,’ March 2, 1887), as having shown that a marl rich in lime, with which 
Schultz-Lupitz marled his soil, constantly yielded nitric acid after being boiled out 
with water, by which it is supposed it would be sterilised; and this was the case when 
the mass was exposed to ammonia-free air. According to the results obtained, a 
kilogram of the mass would acquire nearly a gram of nitric acid per annum. Pure 
calcium carbonate acted in a similar manner. After being washed out with hot water 
on a large filter, and kept moist, but protected from dust, nitrification took place. 
Frank considers tlie calcium carbonate of the soil as a nitrogen combiner; and that, 
