86 EARTHS. 



Muriate of aynmonia wxi called sal ammoniac 

 from its having been originally brought from the 

 neighbourhood of the Temple of Jupiter Ammon. 

 It is now abundantly prepared in this country by 

 saturating carbonate of ammonia with sulphuric 

 acid, which forms sulphate of ammonia : by de- 

 composing this salt by muriate of soda, muriate of 

 ammonia and sulphate of soda are obtained. Sal 

 ammoniac is employed in many processes. 



EARTHS. 



At the first view it would seem, from the vast 

 variety of soils on the surface of the globe, and 

 the number of rocks and stony substances, that the 

 different earths of which they are composed 

 were innumerable : nevertheless, their number is 

 very limited, and, by the mixture of these, the 

 greatest part of mineral bodies is composed. 



The earths were formerly considered as ele- 

 mentary substances, but late discoveries have 

 shown that most of them are, like the alkalies, me- 

 tallic oxides. It is found, however, more conve- 

 nient still to consider them as a separate class. 



The earths are of two kinds : 



1. Those which have some of the properties of 

 alkalies and which are called alkaline earths. 



2. Earths simply so called. 



The alkaline earths are, lime, magnesia, barytes, 

 and strontia. They unite with acids forming com- 

 pound salts as alkalies do : like tliem they change 

 vegetable blues to green ; they have a considerable 

 degree of causticity and taste, and are soluble in 

 water. 



