to an earlier series of experiments made in 1850, I showed that, if a quantity of dry peat be taken and ammonia poured on it, its smell disappears; and this may be continued until upwards of 1.5 per cent of dry ammonia has been absorbed, and this quantity is _retained_ by the peat. In this case pure ammonia was used, but Way's experiments having shown that this alkali is not absorbed from its salts by organic matters, I expressed the opinion that humate of lime (which certainly exists in most soils) ought on chemical grounds to decompose the salts of ammonia and cause the retention of their base. The recent researches of Brustlein have shown that lime does cause the organic matters to absorb ammonia from its salts. He confirms the fact that pure ammonia is absorbed by peat, and shows that decayed wood has the same effect, although both are without action on solutions of its salts. A stiff clay, on the other hand, containing organic matters and much carbonate of lime, readily absorbed ammonia, both when pure and combined; but after extracting the lime by means of a dilute acid, it lost the power of taking it from its salts, although it retained the free alkali as completely as before. On the addition of a small quantity of lime, it again acquired the power of withdrawing ammonia from its compounds. These experiments may be explained, either on the supposition of the presence of humate of lime, or by supposing that the carbonate of lime first decomposed the salts of ammonia, and that the liberated alkali combined with the organic matter. It must be admitted, however, that it is very doubtful whether the ammonia and other substances are fixed in the soil by a true chemical combination. They are certainly retained by a very feeble attraction, for it appears from Brustlein's experiments that ammonia may be, to a considerable extent, removed by washing with abundance of water, and that if the soil which has absorbed ammonia be allowed to become dry in the air, it loses half its ammonia, and after four times moistening and drying, three-fourths have disappeared. These facts are certainly not incompatible with the presence of a true chemical compound, for the humate of ammonia is not absolutely insoluble, and many cases occur of actions taking place in the presence of water, which are entirely reversed when that fluid is removed; and it is quite possible that when humate of ammonia is dried in contact with carbonate of lime, it may be decomposed, and carbonate of ammonia escape. There are other circumstances, however, which render it, on the whole, most probable that the combination is not wholly chemical, but rather of a physical character, among which may be more especially mentioned the fact, that the quantity of the substances retained by the soil is dependent on the degree of dilution of the fluid from which they are taken; and that the quantity absorbed never exceeds a very small fraction of the weight of the soil.