676 



THE SOUTHERN PLANTER. 



is exerted with various energy towards 

 different gases. 



Bodies which absorb the gas or vapour* 

 of water are called hygroscopic. This 

 property of a soil is of the utmost agri- 

 cultural importance, because : Isl — it is 

 connected with the permanent moisture 

 which is necessary to vegetable existence, 

 and, 2d — since the absorption of water- 

 vapour determines the absorption of other 

 vapours and gases. 



In the following table from Schiibler we 

 have the results of a series of experiments 

 carried out by that philosopher, for the 

 purpose of determining the absorptive 

 power of different kinds of earths and soils. 

 He found that dry earths did not absorb 

 oxygen ; this is because being in constant 

 contact with air they were saturated with 

 this gas before the experiments begun ; 

 when, however, the soil was wet wiih 

 water, an absorption was found to occur. 

 The first column of figures gives in thou- 

 sandths the quantity of oxygen absorbed 

 by the moist soil during thirty days ; the 

 second column the quantity, also in thou- 

 sandths, of moisture absorbed by the pre- 

 viously dried soil, in twenty-four hours. 

 Quartz sand, ....10 



Gypsum, 1.7 1 



Lime-sand, .... 4 3 

 Plough land, . . . 10.5 23 



Clay soil, (60 per cent, clay,) 6 28 

 Slaty marl, .... 7 33 

 Loam, .... 7 35 



Fine Carbonate of lime, . 7 35 

 Heavy clay soil, (80 per cent, clay,) 9 41 

 Garden mould, (7 per ct. humus,) 11.5 52 

 Pure clay, . . . . 10 49 

 Carbonate of Magnesia, (fine pow- 

 der,) .... 11 82 

 Humus, . . . . 13 120 



It is seen, that with two exceptions, the 

 rate of absorption for oxygen and for 

 watery vapor increases in the same order. 

 ;it is probable then that the oxygen was to 

 some degree absorbed and held in solution 

 !by the water with which the earth was 

 moistened. The two exceptions are soils 

 rich in vegetable matter, (humus.) They 

 absorbed proportionally more oxygen for 

 a chemical reason ; it united with their 



* The term Gas is applied to permanently 

 :sriform bodies — Vapor to such as readily as- 

 sume a liquid state. The difference is only rel- 



carbon and hydrogen, forming carbonic 

 acid and water. Probably the larger share 

 of the absorption of oxygen, in most cases, 

 was due to this combination of it with the 

 elements of humus, or with the protoxyd 

 of iron, the latter passing thereby into the 

 peroxyd ; but in case of magnesia and car- 

 bonate of lime the absorption must have 

 been a surface condensation. 



An obvious practical result follows from 

 the facts expressed in the above table, viz : 

 that sandy soils which have little attrac- 

 tive force for watery vapor, and are there- 

 fore dry and arid, may be m.eliorated in 

 this respect, by admixture with clay, or 

 better with humus, as is done by green 

 manuring. The table gives us proof that 

 gypsum does not exert any beneficial ac- 

 tion in consequence of attracting moisture. 

 Humus, or decaying vegetable matter, it 

 v/ill be seen, surpasses every other ingre- 

 dient of the soil in absorbing moisture. 

 This is doubtless in some degree connected 

 with its extraordinary porosity or amount 

 of surface. How the extent of surface 

 alone may act, is made evident by com- 

 paring the absorbent power of carbonate 

 of lime, in the two states of sand, and of 

 an impalpable powder. The latter it is 

 seen, absorbed twelve times as much va- 

 por of water as the former. Carbonate 

 of magnesia stands next to humus, and it 

 is worthy of note that it is a very light and 

 fine powder. 



Finally, it is a matter of observation 

 that "silica and lime in the form of coarse 

 sand, make the soil in which they predom- 

 inate so dry and hot that vegetation per- 

 ishes from w^ant of moisture ; when, how- 

 ever, they occur as fine dust, they form 

 too wet a soil, in which plants perish from 

 the opposite cause." Hamm's Landwirtks- 

 chaft. 



ill. Permeahilitij of the soil to water , in- 

 cluding percolation and capillarity. — A soil 

 is permeable to water when it allows that 

 liquid to soak into or run through it. To 

 be permeable is of course to be porous. 

 On the size of the pores depends its 

 degree of permeability. Coarse sands 

 and soils which have few but large 

 pores or interspaces, allow water to run 

 through them readily — water percolates 

 them. When instead of running through, 

 the water is largely absorbed and held by 

 the soil, the latter is said to possess great 

 capillary power ; such a soil has many and 



