IODINE. BROMINE. ACIDS. 65 



228. Iodine occurs in plants as iodides, or compounds 

 of iodine with some metal, as, for example, the iodide of 

 potassium. Bromine is found in a similar state, that is, 

 as bromides. 



229. Bromine is a heavy, brownish liquid, of a suf 

 focating odor. When scarcely perceived, this odor is not 

 unpleasant, and this, with the odors of iodine and of 

 chlorine, forms probably the pleasant smells we perceive 

 on a sea-beach. 



230. These are the principal and the most important 

 mineral substances found in vegetables. 



But a metal called Aluminum, which is the basis of clay, 

 and also the metals Manganese and Copper are found, 

 very rarely, in the ashes of some plants. 



281. Arc all the substances necessary to the growth of 

 a plant, of equal value? All are essential. If any one 

 of the whole number be absent, the plant will not thrive ; 

 but all are not needed in the same quantities. 



232. The Acids most important in the structure of 

 plants are carbonic acid, sulphuric acid and phosphoric 

 acid, either by themselves, or united with substances with 

 which they form salts, such as carbonates, sulphates and 

 phosphates. These are found in all plants. Silicic acid 

 combined with the alkalies and with the earths is also 

 essential to very many plants. 



233. But these are not the only acids found in plants. 

 By a peculiar action of the vital power of particular 

 plants, the elements of carbonic acid and water form a 

 variety of acids differing from carbonic acid and from 

 each other. 



The acid which gives to apples their characteristic taste, 

 is called malic acid (Lat. malum, an apple.) The acid of 

 oranges and lemons is citric acid, (Lat. citrus, an orange ;) 



