ALUMINUM. 



285 



this the radium salt is prepared by repeated fractional crystallization. The 

 small yield of radium obtained after long and tedious operations make it the 

 most costly material of the day. 



Both the chloride and bromide of radium are white, crystalline substances 

 turning grayish in the course of time. Lack of a liberal supply of radium has 

 so far prevented a closer study of its chemical behavior. 



Summary of analytical characters of the alkaline earth-metals. 



26. ALUMINUM. 



Al iu 27 (26.9). 



Aluminum is the representative of the metals of the earths proper ; 

 all other members of this class are found in nature in very small 

 quantities, and are chiefly of scientific interest, with the exception of 

 cerium, which furnishes an official preparation. 



Occurrence in nature. Aluminum is found almost exclusively 

 in the solid mineral portion of the earth ; rarely more than traces of 

 aluminum compounds are found dissolved in water, and the occur- 

 rence of aluminum in the animal organism seems to be purely 

 accidental. 



By far the largest quantity of aluminum is found in combination 



