HU′MUS

Syn. Ulmin . When wood, or woody fibre, is exposed to the joint action of air and moisture, it suffers eremacausis or decay, and crumbles down into a dark-brown or black powder commonly called ‘mould,’ and to which chemists have given the name of ‘humus.’ In this state it exists in fertile soils, in which it is derived from the decay of plants. A powder reagents on sugar, lignin, . When acted upon by dilute boiling solution of caustic pota a, this substance yields a deep-brown solution, from which acids precipitate a flocculent brown substance generally called ‘ulmic’ or ‘humic acid.’ Both bodies require further investigation, as they are supposed to vary exceedingly in composition.