HUMMELLER. 



HUMUS. 



HUMMELLER, BARLEY. An instrument 

 for separating the awns of the barley plant 

 from the seed. There are various modes of 

 taking off the awns : a common one is by tread- 

 ing it by a horse walking over it ; another, by 

 rolling it with a grated roller, an instrument 

 something similar to a garden roller, the cylin- 

 der being formed of thin, flat, wrought iron 

 bars, placed about two inches apart, and the 

 edges to the surface : this, rolled over the bar 

 ley, takes off the awns or ailes. We have also 

 seen a grated presser or chopper, about a foot 

 square, barred across with thin plates, which 

 is lifted up and down by the workman, and 

 thus chops off the awns. But the best machine 

 we have seen is one upon a wood stand, with 

 a hopper into which the barley is thrown, from 

 whence it falls into a box in which a spindle is 

 placed in an inclined position, having, when at 

 a few inches apart, short knives placed spiral- 

 ly, so as to form a sort of screw, which, when 

 put in motion, has a tendency to draw the bar- 

 ley from the upper end of the box to the lower: 

 during the operation the awns of the barley are 

 effectually knocked off. This mode of dressing 

 barley constitutes one of the principal improve 

 ments in Sailer's patent winnowing machine, 

 which will be described hereafter; but the 

 hummeller is made in the form described for 

 barley only, by several makers. See WINNOW- 

 ING MACHINE. 



HUMUS. A modern term given by some 

 chemists to the very finely divided organic 

 matters which all cultivated soils contain, and 

 which is generally regarded as the chief ele- 

 ment of fertility, the source from which plants 

 are directly nourished. Woody and vegetable 

 fibre in a state of decay constitutes the sub- 

 stance called humus. Liebig lays it down as 

 established, that man and other animals derive 

 the means of their growth and support from 

 the vegetable kingdom, whereas plants find 

 new nutritive material only in inorganic sub- 

 stances. According to this doctrine, humus, 

 being the product of organic matter, does not 

 contribute direct nourishment, to plants, but 

 only constitutes a medium and agent through 

 which their nutriment is derived. "The opi- 

 nion," he observes, "that the substance called 

 humus is extracted from the soil by the roots of 

 plants, and that the carbon entering into its 

 composition serves in some form or other to 

 nourish their tissues, is so general and so 

 firmly established, that hitherto any new argu- 

 ment in its favour has been considered unne- 

 cessary; the obvious difference in the growth 

 of plants, according to the known abundance 

 or scarcity of humus in the soil, seemed to afford 

 incontestable proof of its correctness. 



"Yet this position, when submitted to a strict 

 examination, is found to be untenable ; and it 

 becomes evident from most conclusive proofs 

 that humus, in the form in which it exists in the 

 soil, does not yield the smallest nourishment to 

 plants. 



"The adherence to the above incorrect opi- 

 nion has hitherto rendered it impossible for the 

 true theory of the nutritive process in vegeta- 

 bles to become known, and has thus deprived | 

 Xis of our best guide to a rational practice in 

 agriculture. Any great improvement in that | 

 648 



most important of all arts is inconceivable 

 without a deeper and more perfect acquaint- 

 ance with the substances which nourish plants, 

 and with the sources whence they are derived ; 

 and no other cause can be discovered to ac- 

 count for the fluctuating and uncertain state of 

 our knowledge on this subject up to the present 

 time, than that modern physiology has not kept 

 pace with the rapid progress of chemistry." 



The chemical process through which humug 

 is usually obtained, is by making an alkaline 

 solution or decoction of mould, peat, soot, 

 woody fibre, &c., and adding to such decoction 

 acids. The flocculent matter precipitated is 

 called humic acid, a substance but slightly so- 

 luble in water, requiring no less than 2500 

 times its weight for this purpose. The com- 

 pounds which it forms with alkalies, lime, and 

 magnesia, have the same degree of solubility. 

 (Sprengel.) 



" Vegetable physiologists agree in the suppo- 

 sition that by the aid of water humus is rendered 

 capable of being absorbed by the roots of 

 plants. But, according to the observation of 

 chemists, humic acid is soluble only when 

 newly precipitated, and becomes completely 

 insoluble when dried in the air, or when ex- 

 posed in the moist state to the freezing tempe- 

 rature. (SprengeL} 



" Both the cold of winter and the heat of 

 summer, therefore, are destructive of the solu- 

 bility of humic acid, and at the same time of 

 its capability of being assimilated by plants ; 

 so that, if it is absorbed by plants, it must be 

 in some altered form. 



"According to Dr. Jackson, the substances 

 contained in humic extract form soluble salts 

 with lime. The acids form soluble salts with 

 the same substance, and the salts are decom- 

 posed in the process of vegetation. 



" The correctness of these observations is 

 easily demonstrated by treating a portion of 

 good-mould with cold water. The fluid remains 

 colourless, and is found to have dissolved less 

 than 100,000th part of its weight of organic 

 matters, and to contain merely the salts which 

 are present in rain-water. 



" Decayed oak wood, likewise, of which hu- 

 mic acid is the principal constituent, was found 

 by Berzelius to yield to cold water only slight 

 traces of soluble materials; and I have myself 

 verified this observation on the decayed wood 

 of beech and fir. 



"These facts, which show that humic acid 

 in its unaltered condition cannot serve for the 

 nourishment of plants, have not escaped the 

 notice of physiologists ; and hence they have 

 assumed that the lime or the different alkalies 

 found in the ashes of vegetables render soluble 

 the humic acid, and fit it for the process of as- 

 similation. 



"Alkalies and alkaline earths do exist in the 

 different kinds of soil in sufficient quantity to 

 form such soluble compounds with the humic 

 acid. 



" Other considerations, of ! igher nature, 

 confute the common view respecting the nutri- 

 tive office of humic acid, in a manner so clear 

 and conclusive, that it is difficult to conceive 

 how it could have been so generally adopted. 



" Fertile land produces carbon in the form 





