EARTHS. 17 
them, though with less energy, all kinds of animal 
substances. From these circumstances it has some- 
times been denominated an alkaline earth. Saturated 
with sulphuric (24) and carbonic acid (26), it consti- 
tutes the minerals denominated sulphat and carbonat of 
barytes (196). It has been discovered to have a me- 
tallic base, which is called barium. 
39. Strontian is an earth which, like barytes, is not 
found otherwise than in combination with sulphuric and 
carbonic acids. It occurs in various parts of the world, 
and, when purified, forms a porous mass of greyish 
white colour, acrid taste, and somewhat alkaline nature. 
This earth Converts vegetable blue colours to green, 
but does not act so strongly on animal bodies as barytes, 
nor is it poisonous, like that substance. 
40. Lime, the basis of all those substances which are 
denominated calcareous, is only to be obtained in a state 
of purity by artificial process. Combined with carbo- 
nic acid (26) it forms limestone (140), chalk, and marble; 
all of which are capable of being converted into lime by 
burning. Lime may also be obtained from oyster and 
other sea shells. When pure, it is of white colour, and 
moderately hard substance, though it is easily reducible 
to powder. Its taste is burning and acrid; and, like 
the alkalies, it changes vegetable blue colours to green. 
It has likewise the property of corroding and destroying 
animal substances. Lime, when pure, absorbs water 
rapidly, becomes hot, and falls into powder. Even if 
exposed to the open air it gradually attracts moisture, 
and assumes a powdery form ; soon after which it be- 
comes saturated with carbonic acid (26) from the at- 
mosphere, and is thereby again converted into carbonat 
of lime (140). It occurs abundantly in almost every 
