Manures may be beneficial to plants by affording carbonic acid gas to their roots. Animal and vegetable matters evolve this gas while putrify-ing; but we are not aware of any manure that absorbs it from the atmosphere, so as to be for that reason beneficial to vegetation. Lime attracts carbonic acid gas from the air rapidly, but combines with it so strongly, that it is useless to the plant until the carbonate of lime so formed is imbibed and elaborated by that plant.

It is to its power of gradually forming carbonic acid gas that charcoal partly owes its value as a manure. The chemical operation of charcoal, when employed for this purpose, is by no means so well understood as that of most other fertilizing additions to the land. That the carbon of the charcoal operates so beneficially upon plants, among other modes by a gradual combination with oxygen, hardly admits of a doubt. Liebig gives the results of a series of experiments by Lukas on the use of charcoal as a manure, which seem to corroborate his opinion. From the facts which these chemists, however, adduce, it is evident that the beneficial action of charcoal, as a fertilizer, depends upon the presence of other substances besides carbon. Liebig notes (Organic Chem., p. 62) that "plants thrive in pow-^ dered charcoal, and may be brought to blossom, and bear fruit, if exposed to the influence of the rain and the atmosphere. Plants do no not, however, attain maturity under ordinary circumstances in charcoal powder when they are moistened with pure distilled water instead of rain or river water.

Rain water must, therefore, contain within it one of the essentials of vegetable life; and it has been shown that this is the presence of a compound containing nitrogen; the exclusion of which entirely deprives humus and charcoal of their influence on vegetation.7' It is ammonia, to whose presence in rain water Professor Liebig thus refers, in whose valuable work (p. 207) the experiments of Lukas will be found. From these we learn that in a division of a low hothouse, in the Botanic Garden at Munich, a bed was set apart for young tropical plants; but instead of being filled with tan, as is usually the case, it was filled with powdered charcoal, the large pieces of charcoal having been previously separated by means of a sieve. The heat was conducted by means of a tube of white iron into a hollow space in this bed, and distributed a gentle warmth, sufficient to have caused tan to enter into a state of fermentation. The plants placed in this bed of charcoal quickly vegetated and acquired a healthy appearance.

As always is the case in such beds, the roots of many of the plants penetrated through the holes in the bottom of the pots, and then spread themselves out; but these plants evidently surpassed in vigor and general luxuriance plants grown in the common way; for example, in tan.

M. Lukas then gives a list of several of the exotic plants upon which charcoal appears to have produced the most beneficial effects. It appeared also to promote the rapid germination of seeds. He then proceeded to try the effects of charcoal when mixed with vegetable mould, all of which answered very well. "The charcoal," continues M. Lukas, "used in these experiments was the dust-like powder of charcoal from Firs and Pines. It was found to have most effect when allowed to lie during the winter exposed to the action of the air. In order to ascertain the effects of different kinds of charcoal, experiments were also made upon that obtained from the hard woods and peat, and also upon animal charcoal; although I foresaw the probability that none of them could answer so well as that of Pine wood, both on account of its porosity and the ease with which it is decomposed. The action of charcoal consists primarily in its preserving the parts of plants with which it is in contact, whether they be roots, branches, leaves, Ac., unchanged in their vital power for a long space of time, so that the plant obtains time to develop the organs for its further support and propagation.

There can scarcely be a doubt, also, that the charcoal undergoes decomposition; for, after being used for five or six years, it becomes a coaly earth. It exercises likewise a favorable influence by absorbing and decomposing the matters excreted by the roots of plants, so as to keep the soil free from the putrifying substances, which are often the cause of the death of the spongioles. Every experiment,"concludes M. Lukas, " was crowned with success, although plants belonging to a great many different families were subjected to trial." - (Ibid., p. 211).

Professor J. F. Johnston (Elm. of Ag. Chem., p. 142) recognizes the good properties of charcoal as "a valuable mixture with 'liquid manure, night-soil, farm-yard manure, ammoniacal liquor, or other rich applications to the soil." And as he observes in another place, when speaking of the fertilizing portions of farm-yard drainage, (Trans. High, Soa, 1846, p. 190,) "The only substance at present known, by which the separation of all the valuable in gradients from liquid manure can be fully effected, is animal charcoal. A sufficient supply of this substance, when intimately mixed with the liquid manure, will take up nearly the whole of the saline and coloring matters it holds in solution, will carry down the substances it holds in suspension, and will leave the water nearly pure and colorless. The refuse of the prussiate of potash manufactories will have this effect, and what remains when ivory-black is digested in spirit of salt (muriatic acid) will do still better; but this kind of charcoal is neither cheap nor abundant, and, therefore, cannot be recommended for general use.

The refuse animal charcoal of our manufactories is now sold for manure at the price of several pounds a ton: either those who sell it, or those who use it, might render it still more valuable by causing fermenting liquid manure to filter through it before it is applied to the land.

" But other kinds of charcoal possess this property to a certain extent: wood charcoal, reduced to powder, charred sawdust, and charred peat, are all capable of being used with advantage in extracting the ammoniacal and other salts, which give its value to the liquid of our farm-yards. Experiment has shown that when filtered through a bed of such charcoal, the liquid escapes without color, and almost without taste, while the charred peat or sawdust is converted into fertilizing manure. A great portion of the loss now incurred may be prevented by the use of such kinds of charcoal; and the fertilizing substance may, through their means, be applied to our crops at seasons of the year for which, in their liquid form, they tore not suited. It is even capable itself of yielding slow supplies of nourishment to plants; and it is said in many cases, even when unmixed, to be used with advantage as a top dressing. In moist charcoal the seeds of the gardener are found to sprout with remarkable quickness and certainty, but after they have sprouted they do not continue to grow well in charcoal alone." - (7. W. Johnson's Modern Agricultural Improvements.) - J., in Cottage Gardener.