24 CHEMISTRY, GEOLOGY 



in soils and plants ; but it is usually, when found 

 at all, only in very small quantities. 



SILICIA is the name by which the chemist 

 designates the several varieties of flint, rock- 

 crystal, sand-stone, etc. 



CHLORINE is a gas having a strong, suffo- 

 cating smell, and a greenish-yellow color. It is 

 twice and a half heavier than the atmosphere 1 . 

 A taper burns in it with a dull, smoky flame. It 

 takes the color out of almost all vegetable sub- 

 stances ; hence it is sometimes called the bleaching 

 gas. One hundred pounds of common salt contain 

 sixty pounds of chlorine. [See Appendix, 12. | 



SULPHURIC ACID is often called oil of 

 vitriol, but the first is its proper name. It is 

 made by burning brimstone and saltpetre in 

 leaden chambers, containing water on their floors. 

 It is exceedingly sour, and decomposes vegetable 

 or animal substances when poured upon them. 

 Sulphuric acid is found in gypsum, alum, Epsom 

 salts, and many other substances. Combined 



Questions. What is silicia ? What is chlorine? Is it 

 heavier than the atmosphere ? How much heavier ? How 

 does a taper burn in it ? Why is it called the bleaching gas ? 

 How much chlorine is there in one hundred pounds of com- 

 mon salt ? What is sulphuric acid often called ? How is it 

 made ? What effect has it on organic substances ? In what 

 is it found ? 



