COMPOSITION OF PLANTS 51 



m<i plants is usually spoken of as phosphoric 



ACID. 



48. Silicon. — This is a solid element, which, com- 

 bined with OZJgen, makes sand, or quartz rock. Silicon 



occurs free, but always combined with some other 

 element, usually oxygen. Its compounds are called 

 sii.k I ombined with oxygen and other elements, 



notably potassium and sodium, it is found in the ashes 

 of plants. 



49. Chlorine. — This element is a gas with a very dis- 

 agreeable odor. It is very active, combining readily 

 with many other elements. With sodium it forms salt, 

 which is widely distributed over the earth. Compounds 

 of chlorine with other elemental arc called 0H&0BTOB8, 

 and they are found in the ishep of all plants. 



50. Potassium. — This is a solid element, which al- 

 ocenn in combination. It eombmei very readily 



with water, and forms what W€ know as DTI or JOl L8B 



It tbo eombinei with chlorine, forming I 

 pound retembling mil and known as POTASSIUM cm.o- 

 i;ii)i:. oommonly called miimxtk OF potash. On the 

 farm thifl com pou nd is much used as a frrt ilizt-r. It 

 combines with oxygen and oaibon to form potassium 

 c\hho\\ti:. In some form it is found in the as! 

 all plants. 



51. Sodium. — This is another solid (dement, which 

 closely resembles potassium. It never occurs free, hut 

 always in combination. It forms compounds very simi- 

 lar to those formed by potassium. With water it forma 

 soda lyb; with chlor and with carbon and 

 oxygen, sodium carbon ats. It occurs in some form in 



