EARTHS. 



EARTHS. 



in soils ; they give absorbent power to the soil 

 without giving it tenacity: sand, which also 

 destroys tenacity, on the contrary, gives little 

 absorbent power. I have compared the ab- 

 sorbent powers of many soils with respect to 

 atmospheric moisture, and I have always found 

 it greatest in the most fertile soils ; so that it 

 affords one method of judging of the produc- 

 tiveness of land. 1000 parts of a celebrated 

 soil from Ormiston, in East Lothian, which 

 contained more than half its weight of finely 

 divided matter, of which eleven parts were 

 carbonate of lime, and nine parts vegetable 

 matter, when dried at 212 gained in an hour, 

 by exposure to air saturated with moisture at 

 a temperature of 62, 18 parts; 1000 parts of 

 a very fertile soil from the banks of the river 

 Parret, in Somersetshire, under the same cir- 

 cumstances, gained 16 grains ; 1000 parts of a 

 soil from Mersea, in Essex, worth forty-five 

 shillings an acre, gained 13 grains; 1000 grains 

 of a fine sand from Essex, worth twenty-three 

 shillings an acre, gained 11 grains ; 1000 of a 

 coarse sand, worth fifteen shillings an acre, 

 gained only 8 grains; 1000 of the soil of Bag- 

 shot Heath gained only 3 grains." 



In my own experiments upon the absorbent 

 powers of various earths, I extended the ex- 

 amination to various organic and saline fer- 

 tilizers. The result of these may be seen in 

 the following table : 



Parts. 



1000 parts of horse dung dried in a temperature of 

 100 degrees, absorbed, by exposure for three 

 hours to air saturated with moisture and of the 

 temperature of 62 degrees - 



1000 parts of cow dung, under the same circum- 

 stances, absorbed .--... 

 1000 parts pip dung ...... 



1000 sheep dung ------ 



1000 pigeon's dung . _ - - - 

 1000 of a rich alluvial soil, worth two guineas 

 per acre (rent), -------14 



The following were dried at 212 degrees: 



1000 parts fresh tanner's bark - - - - 115 

 1000 putrefied tanner's bark - 



refuse marine suit sold as manure 



soot ...... 



burnt clay ..... 



coal ashes ..... 



lime ---... 



sediment from saltpans 



crushed rock salt - 



- 145 



130 

 120 

 81 

 50 



1000 



1000 



1000 



1000 



1000 



1000 



1000 



1000 



1000 



gypsum 

 chalk 



145 

 491 

 36 

 29 

 14 

 11 

 10 

 10 



9 



4 



(Johnson on Fertilizer*, p. 41.) 

 Davy's experiments and my own are con- 

 firmed by those of M. Schubler, who varied his 

 observations at intervals of three days; his 

 results were as follows : 





Another property possessed by all cultivated 

 soils, that of absorbing the gases of the atmo- 



sphere and of putrefaction, is a power equally 

 worthy of the consideration of the farmer. It 

 was long since shown, in some experimental 

 researches of Mr. Hill, that when oxygen gas 

 is supplied to the roots of plants, their growth 

 and vigour are very considerably increased. 

 Some years since, also, Alexander Von Hum- 

 boldt announced that the earths possess the 

 property of absorbing this gas from the atmo- 

 sphere (Gilbert's Jin. of Phil. vol. i. p. 512); and 

 although the fact was doubted at the time, yet 

 later researches have shown that moist earth 

 has the property assigned to it by Humboldt, 

 and the amount absorbed by various earths has 

 since been ascertained by, and will be seen in 

 the following table of M. Schubler : 



55 



This attractive power of the earths and 

 of the plants for the aqueous vapour and the 

 oxygen gas of the atmosphere are, as I have 

 on more than one occasion contended, two of 

 the most important facts to be kept in mind by 

 the farmer, with regard to the deepening and 

 pulverization of his soils. The power of ab- 

 sorbing moisture is a power which all plants 

 possess in a certain measure, but some in such 

 a perfect degree as to depend entirely upon it 

 for all the moisture they need. The aloe, the 

 agave, and many of the native plants of the 

 East, nearly support themselves in the same 

 way ; the lichens and some of the mosses of 

 this country also do the same. The quantity 

 of water consumed by plants, when in a state 

 of healthy vegetation, is in fact so great that, 

 if it was not for the gentle steady supply thus 

 imperceptibly furnished to the soil by the at- 

 mosphere, vegetation would speedily cease, or 

 only be supported by incessant rains. Thus 

 Dr. Hales ascertained that a cabbage transmits 

 into the atmosphere, by insensible vapour, 

 about half its weight of water daily; and that 

 a sunflower, three feet in height, transpired in 

 the same period nearly two pounds' weight. 

 (Veg. Stat. vol. i. pp. 515.) Dr. Woodward 

 found that a sprig of mint, weighing 27 grains, 

 in seventy-seven days emitted 2543 grains of 

 water. A sprig of spearmint, weighing 27 

 grains, emitted in the same time 2558 grains; 

 a sprig of common nightshade, weighing 49 

 grains, evolved 3708 grains, and a Lathyrus of 

 98 grains emitted 2501 grains. (Phil. Trans. 

 1699, p. 193.) "The power of soils to absorb 

 moisture," says Davy, "ough't to be much 

 greater in warm or dry countries than in cold 

 or moist ones, and the quantity of clay or vege- 

 table or animal matter greater. Soils, also, on 

 2 O 433 



