QUESTION OP THE SOURCES OF THE XITROGEH OF VEGETATION". 
77 
ill presence of water and atmos^Dlieric air, nitrite and nitrate of lime are gradually 
formed, the nitrogen and oxygen of the air uniting in contact with the porous body, 
and the acid uniting with the lime and expelling carbonic acid.'”" 
Wolff further quotes the observations of Cloez, made more than 30 years ago, in 
which he passed air, first through a solution of potassium carbonate, then through 
sulphuric acid and over pumice moistened with sulphuric acid, for six months over 
various porous substances. He found a formation of nitric acid when the air was 
passed over pieces of brick or pumice moistened v/ith potassium carbonate ; and also 
traces with chalk, chalk marl, and a mixture of kaolin and calcium carbonate. On the 
other hand he found no formation of nitric acid by burnt bones moistened with 
potassium carbonate, or by clay. 
Wolff considers that the conditions of his experiments involved those found by 
Cloez to favour such formation of nitric acid. He admits, however, that it is difficult 
to explain why the action should take place when the Leguminosse are present, and 
that the growth of the cereals is not benefited thereby. He suggests whether the 
greater pumping action of the leaves of the Leguminosoe causes a more active aeration 
of the soil, and so it may be that with their increased development the greater is the 
amount of nitrogenous nutriment accumulated from the atmosphere by the moist soil, 
whilst it is well known that these plants leave an efficient nitrogenous residue for 
succeeding crops. 
In conclusion, Wolff admits that the amounts of absorption indicated in the 
experiments with particular plants cannot be expected on a large scale. In practice, 
soils are not kept so porous, and so constantly moist; nor are the mineral conditions 
of the soil always so favourable. Indeed the variations of result in the different 
experiments illustrate the influence of varying conditions. 
Perhaps the most striking of Wolff’s results were those obtained in the experiments 
made in 1853, in which clover yielded about six times as much dry produce grown in 
an ignited rich meadow soil, as in the same soil in its natural state. The ignited soil 
would not only he nitrogen free, but sterilised; so that, unless it acquired and 
developed micro-organisms during the growth, the supposition of the intervention of 
such agents in bringing free nitrogen into combination within the soil would he 
excluded. In reference to this point it may be remarked, that in the case of 
Helleiegel’s experiments, in which he added the watery extract from various soils to 
his quartz sand, he states that red clover showed no special result. 
Next as to Wolff’s more recent results, in which river-sand was used as soil, in 
some cases unwashed, but in others washed free from the fine matter which contained 
nitrogen. It is, as he says, quite consistent with experience in agriculture, that oats 
and potatoes should yield little increase by mineral manure without nitrogen, but give 
increase much in proportion to the nitrogen supplied to the soil ; and that, on the 
* The above results of Frank have since been called iu question by H. Plate (‘Jahrblicher,’ vol. 16, 
1887, p. 891, and vol. 17, 1888, p. 725); also by Professor Landolt, ‘ Landvv. Presse,’ Jahrgang 15, no. 30. 
