[ 64 1 [BookVt 



CHAP. XL 



JM A G N E S I A N EARTHS. 



?&.'/. Soap Rock. French Chalk..-*- 

 Serpentine Stone. Mica. Talk. Mufcovy Glafs. AJleftos. Mi- 

 neral Cloth. Mountain Leather. Mountain Flax. Mountain 



Wood. 



TO obtain MAGNESIA, the mother water of nitre, 

 or of common fait, is placed in a large veflel, 

 and diluted with a connderable quantity of common 

 water. Fixed alkali difiblved in water is then added, 

 and the mixture juil made to boil. By this procefs the 

 magnefia falls to the bottom of the veflel in the form 

 of a powder, which is purified by repeated affufions 

 of water. Magnefia, in its mild flate, confifts of forty 

 parts magnefian earth, forty- eight carbonic acid, and 

 twelve water. The cryftallized aerated magnefia 

 contains half its weight of carbonic acid, one fourth 

 magnefian earth, and one fourth water. 



Magnefia combined with vitriolic acid conftitutes 

 EPSOM SALT, which in many refpefbs refeinbles Glau- 

 ber's fait j it may be diftinguifned, however, by an 

 cafy experiment j for if a fixed alkali is added to a 

 folution of Epfom fait, n precipitation is produced, 

 which is not a confequence of adding an alkali to a 

 folution of Glauber's fait. Even the volatile alkali, 

 if mild, is capable .of feparating magnefia from its 

 acid, by means of a double attraction; the alkali unites 

 with the vitriolic acid, and part of the earth falls to 

 the bottom, combined with carbonic acid. 



Magnefia enters into the competition of fome earthy 



fubftancesj the itones ufually treated of under this 



6 head 



