CHEMISTRY OF COMMON SALT. 19 



during a period of thirty-six years, some of the most profound 

 thinkers, and, of the most skilful experimenters in the natural 

 sciences of that age, engaged in presenting facts which bear 

 upon the question here under discussion. Scheele recognized 

 in 1774, for the first time, a peculiar gas by treating black oxide 

 of manganese with muriatic acid, which subsequently became 

 better understood by the name of chlorine. Sir Humphrey Davy 

 succeeded, in 1807, in isolating, by means of a powerful electrical 

 battery, the element sodium from caustic soda under proper 

 circumstances. Gay Lussac and Thenard proved, in 1809, by 

 very careful experiments, that the pure salt did not contain the 

 element oxygen as one of its component parts ; they advanced 

 soon after, for the first time, the idea that the peculiar green 

 gas which Scheele had obtained from the muriatic acid ought 

 to be considered an element. Sir Humphrey Davy was the first 

 chemist who, in 1810, adopted the proposition of these illus- 

 trious French savants ; he named that element, on account of 

 its (pale) green color in its gaseous state, chlorine, and pro- 

 duced finally the pure salt from its component parts by burning 

 sodium in chlorine gas. Knowing once its elementary constitu- 

 tion, there remained but little to be done to learn the relative 

 proportion of its component parts. The simple introduction of 

 the balance, whilst repeating Davy's experiment, demonstrated 

 the fact that twenty-three parts of sodium had combined with 

 thirty-five and one-half parts of chlorine, producing fifty-eight 

 and one-half parts of chloride of sodium, i. e., pure salt. Nat- 

 ural solutions of chemically pure salt are not known ; its demand 

 is supplied by saturating pure carbonate of soda with pure 

 muriatic acid. Natural crystals of pure salt may be obtained 

 by separating carefully individual crystals from well developed 

 crystallinic masses of rock salt. I do not propose to treat here 

 in detail of all the highly interesting and important physical 

 and chemical properties of the chemically pure salt, for it would 

 but amount to a more or less accurate copy of our text-books in 

 physics and chemistry, and may be studied from them directly 

 with much greater advantage. What I intend to attempt is to 

 engage your attention for a discussion on " common salt " as 

 known in commerce and industry, with particular reference to 

 its application in the various operations of our agricultural 

 industry. As these operations require a salt of different mechani- 



