40 AGRICULTU.^AL CHEMISTRY. 



here as to potash. We have first metallic sodium (Na), 

 a yellowish-white, shining metal, lighter than water, 

 soft enough to be cut with a knife, that takes fire 

 in warm water. Next, we have this metal, combined 

 with oxygen only, soda, or oxide of sodium (NaO) ; 

 then we have carbonate of soda, (washing soda), 

 (NaO, CO") ; and then bicarbonate of soda, (cooking 

 soda), (NaO, 200^). I have not noticed the water 

 (HO) in the foregoing combinations. The reader will 

 perceive how much of it is consolidated in them by 

 looking at Table II. It is in the form of carbonate of 

 soda (NaO, CO^), or (NaO, C0^ lOHO), if we no- 

 tice the water, that this substance is applied to soils. 

 In this form it is used considerably in England, and 

 is beginning to be used in this country. An im- 

 pure kind of it is sold in the market as soda-ash. It 

 is obtained from the ashes of sea- weeds. 



58. Lime (CaO). — This is an oxide of calcium. It 

 is lime as it comes from the kiln, before exposed to 

 air. Lime in the quarry is the same substance, com- 

 bined with carbonic acid. On being slacked it com- 

 bines with water, 1 atom of water, 9, to 1 atom of lime, 

 28, making 37 for the atom of hydrate of lime. Thus 

 28 lbs. of quick-lime make 37 lbs. of dry slacked lime. 

 Or if left after being taken from the kiln, exposed to 

 the air, it first absorbs moisture, then crumbles to 

 powder, and in a few days takes carbonic acid from 

 the air, and becomes carbonate of lime (air slacked), 

 just what it was in the quarry, except in structure. In 

 tracing the metal, calcium, through some of its combi- 

 nations, we have a course similar to those under pot- 



