071 the Effect of Charcoal on Vegetation. 253 



from manure or humus, but from the air. We come now to a very important 

 point in the nourishment of plants, to which M. Payen has particularly called 

 our attention in two treatises read before the Academy of Sciences at Paris, 

 on the 8th and 14th of October, 1839 : viz, that charcoal operates as a con- 

 denser, under the influence of water, on the constituent parts of the air, in the 

 same manner as spongy platina on the elements of detonating gas ; so that 

 nitrogen and oxygen are dissolved, and, mixing with water, are absorbed by the 

 spongioles, and carried to the cambium for assimilation. This property of 

 condensing the air, and making it fit to be received by plants, does not ex- 

 clusively belong to charcoal, for it is also more or less perceptible in other 

 sorts of earth, chiefly in porous and pulverised bodies. We know that water, 

 even when not distributed through charcoal or earth, absorbs some air, which 

 becomes a watery fluid, and by heating is again expelled in the form of gas : 

 but charcoal powder appears to possess this power in the highest degree ; con- 

 sequently, besides light and heat, is capable of carrying to the roots both air 

 and water, i. e., nitrogen, hydrogen, and oxgyen, in the greatest abundance. 



3. Decomposition of the Charcoal, and Formation of a nouiishhig Substance for 

 Plants, It is well known that manure, as such, does not nourish plants, and 

 that, on the contrary, when it touches the roots it causes disease. We know 

 that it is the constituent parts of the humus, i. e. the matter produced by 

 decay, which nourish plants. This apparently takes place because the 

 humus, with the cooperation of air and water, is continually forming oxide of 

 charcoal, or carbonate and nitrogen, which, together with the saline particles, 

 is absorbed and assimilated by the roots. For a long time it was generally 

 believed that charcoal, as an inanimate body incapable of^decay, contributed in 

 no degree to the nourishment of plants, and that charcoal dust could only 

 serve at most to make the earth looser and warmer. But M. Lucas found, 

 from his experiments, that the charcoal in which plants grow by degrees un- 

 dergoes decomposition, and at last becomes a sort of humus. This obviously 

 takes place merely because the charcoal dust acts as humus, and, with the 

 cooperation of water and air, continually gives out to the plants oxide of 

 charcoal, or carbonate, together with the saline particles which are in the 

 charcoal and remain in the ashes after burning. But, to prove this, some 

 chemical experiments were necessary. 



4. Comparative Chemical Examination of Charcoal Dust. The more perfectly 

 to establish the theory of the effect of charcoal on vegetation, M. Lucas gave 

 me for examination : — 



1st. Ashes of fir charcoal in which no plants had grown. 



2d. Ashes of fir charcoal in which plants had grown for half a year.* 



3d. A portion of charcoal dust which had been used for another purpose 



for two years.f 

 With these materials I made the following comparative experiments : — 

 Two drachms of them were reduced to fine powder, and digested in three 

 ounces of distilled water for 24 hours. All the three quantities, filtered off 

 from the charcoal, were uncoloured, and left the test paper unchanged. After 

 the evaporation of the water, there remained only a very trifling yellowish 

 residuum, of a saltish taste, which acted somewhat like an alkali, and, besides 

 potash, contained also chlorine. No difference could be distinguished in this 

 case between a, b, and c. 



The portions of charcoal powder to which water had been applied were 

 each separately digested in a sand-bath, with three ounces of water, to which 

 a drachm of corrosive lie of potash was added. The liquid filtered from a 

 was almost colourless, and was not the least muddy when saturated with 

 muriatic acid. The liquid from b was brownish, and with muriatic acid yielded 



* This charcoal was used for most of the experiments, 

 t It was used to fill a bed, hence its impurity is easily accounted for. — 

 Liucas. 



