CHAPTER VII. 



CHEMICAL COMPOSITION AND FORMULAS OF MINERALS. 



On a former page a brief explanation is given of the con- 

 stitution of minerals. The following table contains the names 

 of all the elements thus far discovered by Chemistry, to- 

 gether with the abbreviations or symbols by which they are 

 indicated in chemical formulas, and the combining or atomic 

 weights. Thus Al stands for the element Aluminium, Sb for 

 Antimony (derived from Stibium, the Latin name for Anti- 

 mony). As all the elements combine with oxygen, and oxyds 

 (as such compounds are called), are the most common of all 

 compounds, Berzelius proposed to use a dot over a letter for 

 oxygen, that is, one dot for one proportion of oxygen, two for 

 two proportions, three for three proportions, <fec. In this way, 

 Ba means that one part of oxygen is combined with one of 

 Baryum ; the compound is protoxyd of baryum. So £ sig- 

 nifies that five parts of oxygen are combined with one of 

 phosphorus ; the compound is phosphoric acid. Again to 

 express two of Aluminium, a bar crosses the letter A, so that 

 3tl means a compound of three of oxygen and two of alu- 

 minium ; 3?e means three of oxygen and two of iron, or a 

 sesquioxyd of iron. Besides the atomic weights of the ele- 

 ments, the principal occurring oxyds are given, with their 

 atomic weights, and also the percentage of oxygen in each. 



Table of Atomic Weights, 



Aluminium, Al, 



171-25 



Alumina, A-l, 



642-5 (0, 46-7) 



Antimony (Stibium), Sb, 



1612-5 



Arsenic, As, 



937-5 



Baryum, Ba, 



856-25 



Baryta, Ba, 



956-25 (0, 10-45) 



Bismuth, Bi, 



2600 



Boron, B, 



136-2 



Boracic acid, B, 



436-2 (0, 68-8) 



Bromine, Br, 



1000 



