SALTS. 235 



and to substitute the atomic weight of each con- 

 stituent. This conveys a more precise idea of 

 the constitution of the salt, and gives us at the 

 same time the atomic weight of an integrant 

 particle of it. This method will come to be 

 adopted likewise in the analysis of minerals, as 

 soon as we have acquired more definite ideas 

 respecting the chemical constitution of these 

 complex bodies a kind of knowledge into 

 which great progress of late years has been 

 made by Berzelius and his pupils, and capable 

 even at present of a satisfactory developement 

 with regard to many minerals. 



The great use of a table of the composition of Uti % of 

 the salts is to give us an exact knowledge of the 

 weight of each constituent contained in a given 

 weight of the salt. For example, carbonate of 

 soda is a compound of 



1 atom carbonic acid 2-75 

 1 atom soda 4- 



10 atoms water 11-25 



18 



I am in the habit of keeping carbonate of soda 

 in my laboratory in two states; namely, in crys- 

 tals and anhydrous. If I want exactly 4 grains 

 of soda for any particular purpose, I have only 

 to employ 18 grains of the crystallized carbonate, 

 or 6J grains of the anhydrous carbonate ; in 

 either case I am sure of having exactly the 



