DIFFERENT SALINE SUBSTANCES. 



99 



I must use different weights of all the three. When lime-shells 

 are slaked, they absorb much water and become heavier 100 

 pounds of shells become nearly 132 of slaked lime ; so that for 

 every 100 of the former, we ought to add 132 of the latter. 

 Gypsum, again, contains only 33 per cent of lime, or when 

 burned, 41^ per cent ; so that, to try the effects of lime alone 

 in these three several states, we ought to apply on our experi- 

 mental patches the three substances in the proportions of 



Quicklime, 

 Slaked lime, 

 Gypsum, (unburned,) 

 (burned), 



100 pounds 

 132 ... 

 300 ... 

 240 



So, of every other mineral or saline substance we lay upon 

 the land, there is a known quantity, special for each, in which 

 it must be applied if the effect it produces is to be compared 

 with that produced by a known weight of some other substance. 

 The numbers in the following table indicate, in pounds, the 

 relative weights in which the substances named, when in their 

 pure and dry state, ought to be employed in comparative ex- 

 periments with each other : 



