The American Quarterly Journal of Agriculture and Science, 1(1): 112-114 (1845)

CHARCOAL—ITS PROPERTIES AND USES

This substance has excited great attention of late in some portions of the country, although no accurate experiments have yet been made to test its value as a manure. In theory, it is certain that it possesses properties which are calculated to render it a very valuable substance in agriculture. And this arises from a power not peculiar to charcoal. All porous bodies have the property of absorbing the different gases in greater or less quantities. Charcoal, after it has been heated to redness, and cooled without being exposed to the air, will absorb ninety times its own volume of ammoniacal gas, and considerable quantities of others. If heated and cooled under water, and then placed in a confined portion of atmospheric air, it will absorb all the oxygen and leave pure nitrogen. Now, upon this property of absorbing gases depends its use as a manure. In itself, it has no valuable properties. It is one of the most indestructible of substances. Exposed to heat of the greatest intensity, if air is excluded, it suffers no change. Moisture has no effect upon it, and there is no chemical agent which will act upon it. It has been said by some writer, that, after being in the ground for several years, it becomes converted into a sort of coaly earth. But, on the other hand, it is a well known fact that fence posts are often charred at the bottom, in order to preserve them from rotting, and it succeeds for a great number of years. In this case, no such change can have taken place. It is, at any rate, very doubtful if it is ever converted into earth, or, of itself, furnishes any food for plants. But it does absorb gases, and by the powerful condensing force which all porous bodies possess, they are made solid in the pores of charcoal. One cubic inch of charcoal will condense ninety cubic inches of ammonia, or thirty-five of carbonic acid. And, holding it with all this force, how are they to give it off to plants? One class of theorists will say, that the vital power of the plant can separate it. But it is locked up in the pores of the charcoal, where not even the most minute fibre of the roots can penetrate. Others say, it is by the power of fixing gases that it does good, but they do not account for the giving them out. What then is it? Let us look a moment at another fact.

Water absorbs, at the common temperature and pressure, from seven hundred to eight hundred times its volume of ammoniacal gas, and when boiled will not part with the whole of it. Now notice the difference: charcoal absorbs ninety, and water eight hundred times their volume. The superior force of the water is seen at a glance. And what must be the result? Why, simply this: If charcoal is put upon land as a manure, however much gas it may have in its pores, the first shower of rain will separate it and carry it with it into the earth, ready for the use of the plants. In the mean time, the water takes the place of the gas in the pores. As soon as they become dry, and perhaps before, the process of absorption commences again, and again it is washed out.

This view of the case would indicate the use of charcoal as a top dressing to crops. And this we believe to be the correct plan. Buried in the soil, it adds to its looseness, but is not exposed to alternate dry and wet, as when on or near the surface.

But its action in compost heaps, or as an absorbent of the urine of man and animals, depends upon another principle. The general opinion seems to be, that its use is to absorb the gases, ammonia, &c., which are given off during decomposition of animal and vegetable substances. That this is not the case will readily appear, if any one will reflect a moment upon its well known action on animal matter. If meat which has begun to putrefy be packed down in charcoal, it is not only deprived of all bad smell, but the process of putrefaction is immediately stopped. No more gases are formed, and of course none can be absorbed. Its effect in this case is to stop the process of decay. In the same manner, any animal or vegetable substance, if exposed to the action of charcoal may be preserved for any length of time unchanged. What the power is by which this is done we do not pretend to say.

It is not, then, by absorbing gases that it is so useful in these cases, but simply through this power of preventing decay and preserving these matters in their unchanged state. Thus, when used in the compost heap, or when saturated with urine, all the substances it comes in contact with are brought under its influence, and when applied to the soil are gradually separated from it by the rains which fall upon them, and there undergo the decay which fits them to become food for plants.

Charcoal has the property also of preserving vegetable as well as animal substances from decay. And it is probably on this account that it has been found useful in propagating plants from their cuttings. Many remarkable experiments have been made with it, and with great success. Even leaves have taken root in finely powdered charcoal, kept constantly wet.