HUM 



HUM 



HUMMELLER. An implement for 

 the separation of harlev from the 

 glumes or awns. This may be clone 

 by tlie means described under barley. 

 An instrument extensively used in 

 Scotland is formed of a hollow cyl- 

 inder of staves or metal, in which an 

 axis revolves very rapidly. To the 

 axis is attached three sets of cross 

 pieces of wood, which reach nearly to 

 the cylinder, and are at right angles 

 to it. The barley being slowly ad- 

 mitted by a hopper above, enters the 

 cylinder, where it is beaten rapidly 

 by the cross pieces, and perfectly 

 cleaned of awn by the time it escapes 

 from below. 



HUMMING-BIRD. Birds of the 

 genus Trochilus, remarkable for their 

 minuteness, brilliancy, and rapid 

 flight. They live upon the nectar of 

 flowers and on small insects. 



HUMOUR. In anatomy, fluid se- 

 cretions natural to the eye or other 

 parts of the body. 



HUMUS. The decayed carbona- 

 ceous residue of plants, of a dark- 

 brown or black colour, and mouldy 

 smell. It is called by gardeners vege- 

 table mould, and has received the 

 name of humus, humic acid, humin, 

 humic extract, coal of humus, ulmin, 

 ulmic acid, geine, geic acid, apoth- 

 eme, &c., &c. 



Being vegetable matter in a state 

 of decay, its composition is subject 

 to change ; and hence a great num- 

 ber of bodies will be formed by treat- 

 ing it with re-agents, as potash, soda. 

 But Mulder has recently shown that 

 the various bodies enumerated by 

 other chemists, as well as the crenic 

 and apocrenin acids, are no more 

 than woody fibre, cellulose, starch, 

 gum, sugar, and similar vegetable 

 bodies in a progressive state of de- 

 cay ; that by the absorption of oxy- 

 gen, carbonic acid and water are 

 constantly being formed, and pro- 

 gressively the difTerent products of 

 decay. From Mulder we learn that 

 ulmic or humic acid consists of 40 

 carbon, 14 hydrogen, and 12 oxygen ; 

 crenic acid, Cm H12 0|6 ; apocrenic { 

 acid, C^8 H12 Oj4, and that the two 

 latter are not, as Berzelius and oth- 

 406 



ers assert, bodies containing nitro- 

 gen, but only that in the soil the 

 apocrenic acid is usually combined 

 with ammonia. Moreover, Mulder 

 failed to discover in the vegetable 

 mould or humus any other organic 

 bodies than humin and its deriva- 

 tives, with cre'.iic acid and its deriva- 

 tives, acting as acids. The bases with 

 which apocrenic and humic acid are 

 combined are chiefly lime and am- 

 monia. The humates of lime, pot- 

 ash, and soda existing in the soil are 

 either insoluble or sparingly soluble ; 

 the humate and apocrenate of ammo- 

 nia are soluble, and form a brown so- 

 lution. Woody tissue, straw, leaves, 

 and vegetable rubbish, exposed to air 

 and kept moist, and at a temperature 

 above 60. decay or run into erema- 

 causis, producing at first ulmic, cre- 

 nic, and apocrenic acids ; these will 

 combine with bases present, and still 

 continue to decay, giving out water 

 and carbonic acid. The ammonia 

 present participates in this change, 

 and becomes converted into nitric 

 acid. The rapidity of decay is much 

 hastened by the presence of caustic 

 lime, potash, or soda, or by their car- 

 bonates. If air be not freely admit- 

 ted, then gaseous compounds of hy- 

 drogen, carburet of hydrogen, sulphu- 

 retted hydrogen, &c., are formed. 



From this we learn that humus is 

 vegetable matter in the act of decay, 

 the products of which depend upon 

 the age, exposure to air or water, 

 temperature, and similar conditions. 

 But there is a variety called inert hu- 

 mus, as peat, turf, &c., which, from 

 the presence of moisture and absence 

 of air, combined with other causes, 

 decays very slowly ; this may, how- 

 ever, be hastened by drying and free 

 exposure to air, by admixture with 

 putrescent bodies, or by the action of 

 lime and bases. The solution of hu- 

 mus, obtained by boiling potash or 

 soda ash with peat, is not strictly a 

 humate of these alkalies. The hu- 

 mic acid can be precipitated by add- 

 ing the strong mineral acids. The 

 portion of humus not soluble in alka- 

 line solutions is called insoluble hu- 

 mus, humin, coal of humus. 



