CALCAREOUS SOILS. 59 



other earth, except carbonate of magnesia, which, if present, mfght 

 be mistaken for calcareous earth, but which is too rare, and occurs 

 in proportions too small, to cause any material error in ordinary 

 cases, and in soils of this region. 



But if it be only desired to know whether calcareous earth is 

 entirely wanting in any soil or to test the truth of my assertion 

 that so great a proportion of our soils are destitute of that earth 

 it may be done with far more ease than by either of the forego- 

 ing methods, and without apparatus of any kind. Let a handful 

 of the soil (without drying* or weighing) be thrown into a large 

 drinking-glass, containing enough of pure water to cover the soil 

 about two inches. Stir it until all the lumps have disappeared, 

 and the water has certainly taken the place of all the atmospheric 

 air which the soil had enclosed. Bemove any vegetable fibres, or 

 froth, from the surface of the liquid, so as to have it clear. Then 

 pour in gently about a table spoonful of undiluted muriatic acid, 

 which by its greater weight will sink, and penetrate the soil, with- 

 out any agitation being necessary for that purpose. If any calca- 

 reous earth is present, it will quickly begin to combine with the 

 acid, throwing off its carbonic acid in gas, which cannot fail to be 

 observed as it escapes, as the gas that eight grains only of calca- 

 reous earth would throw out, would be equal in bulk to a gill 

 measure. Indeed, the product of a single grain only of calcareous 

 earth would be abundantly plain to the eye of the careful operator, 

 though it might be the whole amount of gas from two thousand 

 grains of soil. If no effervescence is seen even after adding more 

 acid and gently stirring the mixture, then it is absolutely certain 

 that the soil contained not the smallest portion of carbonate^ of 

 lime ; nor of carbonate of magnesia, the only other substance which 

 could possibly be mistaken for it. 



The examinations of all the soils that will be here mentioned were 

 made in this pneumatic apparatus, except some of those which evi- 

 dently evolved no gas, and when no other result was required. As 

 calcareous earth is plainly visible to the eye in all shelly soils, they 

 only need examination to ascertain its proportion. A few examples 

 will show what proportions we may find, and how greatly they 

 vary, even in soils apparently of equal value. 



1. Soil, a black clayey loam, from the top of the high knoll at 

 the end of Coggins Point [then my own farm], on James River, con- 

 taining fragments of mussel shells throughout. Never manured, 

 and supposed to have been under scourging cultivation and close 

 grazing from the first settlement of the country; then (1818) ca- 

 pable of producing twenty-five or thirty bushels of corn and the 

 soil well suited to wheat. Cue thousand grains, cleared by a fine 

 sieve of all coarse shelly matter (as none can act on the soil until 

 minutely divided), yielded sixteen ounce measures of carbonic acid 



