2Q0 SOILS, MANURES, &c. 
becomes cauftic : when perfe&Iy burned, 
it diffolves in water, in the proportion of 
five grains to a pint, and on being 
expofed a fufficient time to the air, it 
recovers its acid, and reverts to the date 
it was in before burning, i. e. it becomes 
mild or effete: in this date it has the 
property of promoting putrefaUion, and 
is infoluble in water, as are the other mild 
calcareous earths ; but like them it effer- 
vefces and combines with acids, thereby 
forming a neutral fait; and this fait, when . 
united with oily fubflances, conftitutes a 
kind of faponaceous mucilage, which, 
in a perfedl ftate, is the proper nutriment 
of plants. Calcareous earths, when re¬ 
duced to a powder, and laid on the 
furface of the foil, are foon wafhed down 
by rains, and their effefts loft. 
Marie, of all forts, is compofed of 
calcareous earth mixed with clay : it is 
o friable 
