64 ELEMENTS OF PLANTS. 



222. The ashes of asparagus, and of other plants which 

 grow naturally near the sea, contain a large portion of 

 common salt, in very minute, regular, cubical particles, 

 called crystals. Now salt is composed of a gas called 

 chlorine, and of the metal sodium, and this salt, common 

 table salt, is called by the chemists Chloride of Sodium. 

 And it is very remarkable that this pleasant and wholesome 

 article in our food should be composed of a substance so 

 ready to take fire as sodium and another like 



223. Chlorine. This is a suffocating and poisonous gas, 

 of a greenish color, whence its name, -(chloros, Greek for 

 green,) which has a great attraction for foul air and for 

 coloring substances, and is therefore employed for disin 

 fecting, or drawing off foul air, and for bleaching, or 

 making things white. 



224. Oxides of two other metals, Magnesium and Iron, are 

 also found in the ashes of all plants, but commonly 

 united with some one of the acids. 



225. The oxide of magnesium is called Magnesia. It is 

 a white, bitterish substance, resembling flour in appear 

 ance, often used in medicine. 



226. Plants growing in the sea, called sea-weeds, 

 such as kelp, oar-weed, rock-weed, &amp;lt;fec., and those growing 

 on the sea-shore, contain, in their ashes, salts of two sub 

 stances, called iodine and bromine. 



227. Iodine is a solid which looks like black lead. 

 \Vhen heated, it throws up a violet colored vapor, whence 

 its name, from a Greek word, (i-o-des,) meaning violet 

 colored. If a polished silver plate be held over this vapor, 

 it becomes firs} of a yellowish color, then violet, then deep 

 bl ii(3, from the combination of the iodine witli the silver. 

 This compound is powerfully noted upon by light, and 

 hence its use in the proers.M s of (lie daguerreotype. 



