534 
Abstract Report of Agricultural Discussions. 
tion which had taken place in it through contact with the porous earth, 
had led to the destruction of the humus and the formation of large 
quantities of carbonic acid. This throws some light upon the very 
startling growths sometimes noticed, especially in the case of root- 
crops. The rapid start of young turnips after a good shower of rain, 
on well-dunged land, arises from the rapid production of carbonic 
acid in the soil; but we look in vain for this result in soils not 
properly cultivated. 
Plants, and root crops especially, not only take up carbon through 
the medium of their leaves, but apparently also in the shape of carbonic 
acid in very large quantities through the medium of their roots ; it is 
especially useful to furnish root crops at an early stage of their 
growth with matters that supply carbon in the shape of carbonic acid. 
Boussingault shows that whilst in calcareous soil there arc in 10,000 
parts of air only 87 of carbonic acid, and in heavy clay soil only 66, 
there are in pasture-soils as many as 179 parts of carbonic acid 
to every 10,000 parts of air. Thus it will be seen that in all these 
instances, the quantity of carbonic acid in the soil is very much larger 
than the quantity resting immediately above it. 
In the next place I have to direct attention to atmospheric am- 
monia, which is, perhaps, the most important constituent of the atmo- 
sphere. For a very long time this was entirely and very pardonably 
overlooked, since the quantity is so small that it cannot be determined 
with anything like precision, and it is necessary to have recourse to an 
examination of the rain or dew to ascertain anything like an approxima- 
tion to the truth. Determinations* of the amount of ammonia and nitric 
acid in rain-water have been made by Messrs. Lawes and Gilhcrt, and 
by Professor Way, and in Franco by M. Bincau, and also by 
M. Boussingault, who has done so much for the progress of scientific 
agricultural chemistry. According to M. Bineau, 1,000,000 parts of 
air contain only about - 2 of ammonia ; the amount varying in different 
seasons. According to these researches, the rain which falls annually 
upon an English acre carries upon the land about 22 lbs. of nitrogen. 
This quantity includes the nitrogen which occurs in rain-water in 
the state of ammonia, as well as that in the form of nitric acid. 
Twenty-two pounds upon an acre is but a small amount,* and 
we have to consider the very important question whether this quan- 
* In the course of a subsequent lecture Professor Voelcker qualified the state- 
ment here made by explaining that he quoted from Baron Liebig's ' Laws of 
Husbandry ' wjjen he assigned these proportions to the ammonia in rain-water. 
Dr. Voelcker then added, " I find that the figures do not correctly represent the 
average amount of ammonia which is present. I mentioned 22 lbs. as the amount 
of ammonia, but 14 His. would be nearer the mark. This correction is important 
in reference to the consideration whether atmospheric ammonia is sufficient to 
meet the requirements or wants of the plants. If it be stated to be half as much 
again as it actually is, that of course makes a difference in our views respecting 
the propriety of supplying ammonia in the shape of manure, or leaving plants to 
find their supply in the atmosphere." The amount of ammonia in rain-water, no 
doubt, varies considerably in different localities, and it is, therefore, not easy to 
give a fair average. On the whole, however, he thought 14 lbs. represents more 
»iearly the average of ammonia in rain-water than 22 lbs. 
