186 TRANSACTIONS OF ROYAL SCOTTISH ARBORICULTURAL SOCIETY. 
air is absorbed, the nitrogen passing on to a gasholder, where it 
is stored. By heating the calcium carbide in a current of 
nitrogen, combination takes place, and a compound of calcium, 
carbon, and nitrogen is formed (calcium cyanamide), which is 
placed on the market under the name of “lime nitrogen.” Lime 
nitrogen is a black powder, not unlike basic slag in appearance, 
which generally smells slightly of acetylene. It is not directly 
a plant-food, but in the soil it is converted gradually into 
calcium carbonate, or chalk, and ammonia, the latter of which 
is absorbed by the soil, to be rapidly converted into a valuable 
plant-food. It is evident that in “lime nitrogen” we are dealing 
with a much more complicated substance than “lime nitrate,” and 
that extensive trials will have to be made, in addition to those 
already carried out, before we can be certain of its value under 
varying conditions of soil and climate. 
23. The Accumulation of Nitrogen in Forest Soils.! 
By ALEXANDER LAUDER, D.Sc. 
In this paper M. Henry discusses the important problem of 
the nitrogen supply of forest soils. He shows that, notwith- 
standing the large amount of nitrogen stored up in the trees and 
removed from the land when the timber is felled, the amount 
of nitrogen in the soil not only does not diminish, but, on the 
contrary, gradually increases. Even under the least favourable 
conditions, as when trees are grown on sand-hills, a gradual 
formation of humus, and consequently a gradual storing up of 
nitrogen, takes place in the soil. 
As an example he takes the case of the forest at d’Hourtin 
(Gironde), sown with the seed of the maritime pine about 1850, 
and now forming a fine pole-forest, the stems being from 
30 to 4o inches in circumference. The soil consisted of nothing 
but sand-hills without a trace of vegetation, and contained no 
nitrogen. Analysis of the soil now shows that, exclusive of 
the surface layer of decaying vegetable matter which was 
carefully removed before the soil was sampled, it contains 1°33 
1 La Forét Accumulatrice d’Azote, par M. E. Henry. (2xtrait du 
Bulletin mensuel des stances de la Société des sctences de Nancy.) 
