ON THE FOOD OF PLANTS. 63 



vegetation. This effect is chiefly owing to the quantity of humine, or 

 humic (ulmique) acid which they contain. 



Humine was first observed in a diseased exudation from the elm, 

 whence it received the name of ulmine. It is said to have been after- 

 wards found in the bark of the fir, peruvian bark, oak, hornbeam, 

 horse-chestnut, and simarouba, but it is doubtful whether it was found 

 in these in a state of health, or by the effect of the agents employed in 

 the decomposition. M. Braconnot, (Ann. Chim., xii. p. 191,) formed it 

 artificially by heating saw-dust in a crucible, with an equal weight of 

 caustic potass. He afterwards found it ready formed in soot, and 

 has formed it with sulphuric acid, saw-dust, and many other vegetable 

 substances, such as starch, sugar, &c. 



M. Polydore Boullay, (Journ. Pharm., 1830,) has found humine 

 in the soil, heath-earth, umber, turf, dung, and in general in the most 

 part of woody or cortical substances in a state of decomposition, such 

 as half charred wood. He also thinks it. is formed during the distillation 

 of wood. It is, therefore, doubtful whether humine ought to be reck- 

 oned among the immediate constituents of living vegetables, or among 

 those of diseased, or accidental decomposition. M. Raspail, (Bull. 

 Sc. Chim. viii. ,p. 333,) thinks humine is formed by the carbonised 

 debris of vegetables, and supposes that it varies according to its mode 

 of production. M. Sprengel, who observed it in soils, gave it the 

 name of humic acid.* 



Humine, when pure and dry, is a black substance, has little taste, 

 no smell, and is insoluble in water, a circumstance which has often 

 caused it to be taken for carbon, in the drainings, for example, of 

 dunghills, in which it is abundant. It is very soluble in spirits of 

 wine, concentrated sulphuric acid, potass, soda, ammonia, and by 

 heat in acetic acid. Water throws it down from its solutions. It 

 combines with all the salifiable bases, whence M. P. Boullay gives it 

 the name of the ulmic acid; but it has no acid'taste, does not redden 

 vegetable blues, and, like the gallic acid, contains only carbon and 

 water, without excess of oxygen. 



A very small quantity of alkali is sufficient to saturate the humic 

 acid, and form a humate (ulmate). AH the alkaline humates are very 

 soluble in water. It is by its combination with potass, that the 

 humine becomes soluble in the canker of the elm, where it was first 

 discovered ; and it is with the union of lime, ammonia, or potass, that 

 the insoluble humine of soils, and of dung, becomes soluble, and 



* I prefer Sprengel's name to ulmic acid, which is too contracted. See " ALPHABET 

 OF SCIENTIFIC GARDEMING." EDITOR. 



