On tht Ahjovhint Powers of difftrtnt Earths. i^of 



and alurtiine gave as much as the latter fingly. But the quantity of abforption muft be dif- 

 tinguiflied from its intenftty. Thus ftrontianite, barytes, and filex, are quickly faturated 

 with moifture, while magnefia and alumine continue to imbibe it for a confiderable time. 

 Tlie effects in mixture depend on thofe qualities combined ; after the filex has ceafed to aft, 

 the alumine perfeveres, and through the intermediate agency of the air, divefts the former 

 of the minute portion of humidity which it had attra£l:ed. But the compounds of the fim- 

 ple earths are ftill more remarkable in their aft'edtion to moifture, fince it furpafles that of 

 their ingredients. Thus, fea fand gives Jo"; whinftone, 8o°; though it confifts one half 

 of filex, and the other half of alumine, and the oxide of iron * in nearly equal parts v and 

 pipe clay, which contains a large proportion of filex, 85 °. It is evident, that the abfor- 

 bent power of earths depends as much on their mechanical condition, as on the fpecies of 

 matter of whiah they are compofed. Whatever tends to harden them diminifhes their 

 cffedl:, and the contrary. Hence the reafon why the a£tion of fire impairs their deficcating 

 quality. Quartz, urged in a blackfmith's forge, gives only 19°; but the fame powder, 

 after being foaked a week in water, gave 35°; and moft probably it would have in time 

 recovered its whole original power. The procefs by which nature gradually divides^ 

 foftens, and difpofes ftony bodies to abforb moifture, is beaurifully illuftrated in the in- 

 ftance of whinftone or bafalt. A piece of folid whinftone gave 80 degrees by the hygrome- 

 ter, another piece rotten and crumbling, gave 86° ; but another portion of the fame rock 

 already reduced to mould, aflbrded 92 f. The ameliorating effcfts of culture is exempli- 

 fied in fea fand : fine fand caufed a drynefs of 70°; fand collected from the paths of a fheep 

 walk near the beach 78°; the fame fand, lately brought into cultivation 85°. Still thefc 

 cffefts are inferior to that of garden mould, which amounts to 95°, and to which decom- 

 pofed whinftone approaches the neareft. Comparing thofe fadls with the property lately 

 difcovered by Humboldt, that the earths attraft the oxygenous portion of the air, we far- 

 ther perceive the intimate concatenation of changes which maintain this niundane fyftcm. 

 The lap of nature is prepared for the reception and developement of the vegetable germs, 

 exhibiting in a reciprocating feries of growth and decay, the ever renovating forms of 

 organic bodies through endlefs fucceffions of cycles. 



Sulphuric acid nearly doubles its deficcating power at every 15 degrees of elevation of 

 temperature, that at zero being 60°. The feveral earths appear to follow progreflions not 

 much diff(;rent. 



The relative effe£ts of different foils maybe afcertained more eaCfy, by altering the con- 

 ftru£lion of the hygrometer. Connefl the two balls by a long bent tube paffed through 

 two corks, and cover and wet them both. In this ftate they are introduced into the wine 



• The oxide of iron and zinc which I have tried, fhewed lefs abforbent powers than the earthy bodies. 



■f- Thofe fpecimens were taken from a remarkable fpot on the fummit of Largo Lau, an elegant conical 

 mountain, which rifes behind this place to the height of about 800 feet above the level of the fea. Tht 

 -whinftone parts into fmall hexagonal columns, of which one of the fides is fonutimes almoft effaced. 



decanters 

 2 



