22 SCIENTIFIC AGRICULTURE. 



37. Chlorine is a heavy gas of a yellowish-green 

 color, found only in combination with other elements. 

 In combination with hydrogen it forms hydrochloric 

 acid, formerly called muriatic acid. If this acid be 

 heated with manganese dioxide, the chlorine will be 

 separated. It is poisonous when breathed. It will 

 destroy organic coloring matters and bad-smelling 

 gases, and hence is used for bleaching, and as a dis- 

 infectant or purifier of air (19). Common salt is a 

 compound of sodium and chlorine. This element 

 is found in the ash of plants and also in soils. 



38. Iodine, a dark-colored solid that forms a 

 beautiful violet vapor when heated, and bromine, 

 a dark-red liquid, are found in combination with 

 other elements in some plants. In chemical proper- 

 ties they are similar to chlorine (20). Fluorine is 

 the most difficult to prepare of all the elements. 

 It is described as a gas, and exists in small quan- 

 tities in the teeth of animals, and in other por- 

 tions of the body, and also in some plants and 

 minerals. 



39. Potassium is a soft metal, lighter than water. 

 It unites with oxygen so readily that it has to be kept 

 under the surface of naphtha, a liquid that has no 

 oxygen in it. If thrown on the surface of water, or 

 placed on a piece of ice, it takes fire and burns with 

 a beautiful violet-colored flame (21). In combina- 

 tion with hydrogen and oxygen, it forms caustic pot- 

 ash. All the acids contain hydrogen. The salts of 

 potassium are formed by replacing the hydrogen of 



