MATERIALS EXISTING IN THE SOIL. 47 



51. Chlorine is a suffocating, unwholesome gas, existing 

 in bleaching liqiioi\ and in common salt, united with the metal 

 Sodium, which is found in soda.* It possesses the property 

 of destroying vegetable colours and the odour of putrefac- 

 tion, and is at present extensively used in bleachmg and 

 in the hospitals for fumigation. 



52. Sulphuric Acid is the important sour liquid, oil of 

 vitriol^ employed so extensively in various manufacturing 

 processes. It is a compound of the well-known substance 

 sulphur with oxygen. It is rarely to be found in a separate 

 state in nature, but exists in a gi-eat many important com- 

 pounds. The compounds formed by its union with alkalies, 

 earths, and metals, are termed sulphates; (7) thus, in Epsom 

 salts, it exists in combination with magnesia, forming sulphate 

 of magnesia; in Glauber salts and salt cake, in combination 

 with soda, forming sulphate of soda; and in gypsum, as already 

 stated, (46) combined with lime, it forms sulphate of lime. 

 The properties of sulphur are familiarly known; it is found 

 in a separate form in Iceland and Sicily ; and, combined with 

 iron, in a mineral called pyrites, in Wicklow, in Ireland. It 

 enters into the composition of several important vegetable 

 compounds, and also forms one-twentieth part of the weight 

 of hair and of the wool of the sheep.f 



53. Phosphoric Acid, or acid of bone earth. The name 

 of this substance is probably not so familiar to you as those 

 we have been considering. You must, however, have heard 

 of phosphoiiis, the curious waxy-looking substance which 

 gives out light in the dark, and when it is rubbed, takes fire. 

 That substance was formerly but little known to the majority 

 of people, and only to be found in small quantities in the 

 shop of the chemist ; but, at present, in lucifer matches and 



• Common salt contains two-fifths of its weight of the metal sodium, 

 combined with chlorine. The compound in the language of chemists is 

 termed chloride of sodium, Chlorine also combines with potassium, the 

 metal which exists in potash, forming a substance termed chloride of 

 potassium, which resembles common salt in appearance, and is occa- 

 sionally used in the manufacture of alum. It exists in the ashes of 

 seaweeds, and is prepared in large quantities by the manufacturers of 

 iodine. 



f It has been calculated that in the wool grown in Great Britain and 

 Ireland erery year, five million pounds of sulphur are abstracted from 

 the soil, to supply which to the plants upon which the sheep live, no 

 less than 13,000 tons of gypsum woiild be required. 



