660 



THE SOU THE 



EN PLANTER. 



[November 



monia and of retaining the base. It was 

 this last fact which led Professor "Way to 

 the erroneous conclusion that organic mat- 

 ters had nothing to do with the absorbing 

 powers of soils. Pure clays, free from the 

 ordinary salts of lime and soda, possess this 

 power in a high degree, and hence it was 

 inferred that the activity of the clay could 

 only be due to some compounds of silica. 

 The double silicates of alumina and potash 

 or soda having the power of forming insolu- 

 ble compounds with ammonia, were sup- 

 posed to be the substances to which the ab- 

 sorbing properties of soils must be ascribed. 



Plenneberg and Stohmann, in repeating 

 the experiments of Way, with the view of de- 

 termining the most favorable conditions un- 

 der which it is necessary to operate in ascer- 

 taining the absorbing power of a soil, found 

 identical results. They have, besides, con- 

 firmed his observation, that absorption di- 

 minishes with the strength of the ammonia- 

 cal solution made use of; and that it is mod- 

 ified according to the relative proportions of 

 the solution and the soil. These two chem- 

 ists, indeed, have found the figures present- 

 ing so great a regularity, as to permit Boe- 

 deckcr to establish an algebraic formula for 

 determining the amount of absorption, on 

 the strength of the solution and the quanti- 

 ties of soil and liquid employed being given. 



Liebig repeated the experiments of Way, 

 and, confining himself exclusively to the 

 properties of arable land, recognized that 

 almost all soils, whether rich or poor in car- 

 bonate of lime or in alumina, possessed the 

 same absorbing power. He ascertained, like 

 Way, that this property does not manifest 

 itself with the same intensity on all the 

 bases — that potash was retained with greater 

 energy than soda, while the whole of the 

 ammonia was retained. The behaviour of 

 alkaline silicate of potash with the soil was 

 the same as the other salts or potash. The 

 base was absorbed at the same time that the 

 greater part of the silica was retained ) and 

 while the absorption of the different earths 

 did not vary much, that of the silka appear- 

 ed to be in the inverse ratio to the organic 

 substances existing in the soil, which, hav- 

 ing generally an acid reaction in saturating 

 the earthy bases, such as chalk and magne- 

 sia, present obstacles to the fixation of silica. 

 Soil taken from a forest, and rich in organic 

 debris, mixed with lime-water until it was 

 alkaline, and afterwards dried, absorbed a 

 large amount of potash and silica. Liebig's 



experiments led him to the conclusion that 

 the absorbing power of soils is due in part 

 to the chemical action of the silicates, and 

 of the hydrates of alumina on the silicates 

 of potash, but that it partly defends on the 

 pltysiccd condition of the soil. 



In consideration of all these facts, Liebicr 

 also came to the same conclusion as Wav^ 

 that the food of land-plants is always pre- 

 sented to them in a special form ; that na- 

 ture had given to the soil the power of ab- 

 sorption, for the special purpose of prepar- 

 ing the food of plants ; — in short, that the 

 soil so far subserved the ends of a stomach 

 for the roots of plants. Both also came to 

 the conclusion that this food existed in the 

 soil in an almost insoluble state. Way, 

 however, believed that it still possessed a 

 degree of solubility sufficient to supply the 

 wants of plants. Liebig, on the other hand, 

 gives his assent to the doctrine (which we 

 believe we were the first broadly to put for- 

 ward) that plants must exercise a dissolving 

 action, by means of their roots, on those 

 substances which are so sparingly soluble in 

 water. We have always thought that, al- 

 though ammonia might be retained in the 

 soil by forming combinations with the dou- 

 ble silicates of alumina and potash, that this 

 was not an essential form of the food of land- 

 plants ; that soluble food, under favorable 

 circumstances, enables vegetables to develop 

 themselves with greater rapidity, notwith- 

 standing that they had also the power of 

 taking up that which was scarcely soluble 

 in water. The experiments, however, of 

 Brustlein afford matter for considering this 

 subject from new and various points of 

 view. 



Brustlein made his experiments at the 

 suggestion of Boussingault, in the laborato- 

 ry of the Conservatory of Arts and Manu- 

 factures. Three kinds of sod were first 

 made use of, each possessing very different 

 physical characters — 1. A tenacious and 

 compact clay, from Bechelbronu, rich in 

 carbonate of lime, capable of retainimg 

 much water, and becoming very hard when 

 dry ; 2. Fertile loam, from the neighbor- 

 hood of Strasburg, rich in carbonate of lime, 

 and very friable ; 3. A quartzose sand, rich 

 in organic remains. In filtering an ammo- 

 niated solution through these different soils, 

 it was found that the amount retained by 

 any soil varied exceedingly with the strength 

 of the solution. Such results were not fa- 

 vorable to the idea of chemical combination 



