BE OMINE- IODINE FL UOIilNE. 241 



sea-water, from which latter it is taken up by sea-plants and many 

 aquatic animals. Iodine is derived chiefly from the ashes of sea- 

 weeds known as kelp. By washing these ashes with water, the soluble 

 constituents are dissolved, the larger quantities of sodium chloride, 

 sodium and potassium carbonates are removed by evaporation and 

 crystallization, and from the remaining mother-liquor iodine is ob- 

 tained by treating the liquor with manganese dioxide and hydro- 

 chloric (or sulphuric) acid : 



2KI -f MnO 2 + 2H 2 SO 4 = K^SO^ + MnSO 4 + 2H 2 O -f 21. 



The liberated iodine distils, and is collected in cooled receivers. 

 Sodium nitrate found in Chili contains a small quantity of sodium 

 iodate, and the mother-liquors, from which the nitrate has been crystal- 

 lized, contain enough iodate to be employed for the preparation of iodine. 



lodins is a bluish-black, crystalline substance of a somewhat 

 metallic lustre, a distinctive odor, a sharp and acrid taste, and a neu- 

 tral reaction. Specific gravity 4.948 at 17 C. (62.6 F.). It fuses 

 at 114 C. (237 F.), and boils at 180 C.(356 F.), being converted 

 into beautiful purple-violet vapors ; also, it volatilizes in small quanti- 

 ties at ordinary temperature. It is soluble in about 5000 parts of 

 water, more soluble in water containing salts, for instance, potassium 

 iodide ; the official Liquor iodi compositus (LugoPs solution) is a 

 preparation based on this property. It contains 5 parts of iodine and 

 10 parts of potassium iodide in 100 parts of aqueous solution. Iodine 

 is soluble in 10 parts of alcohol, very soluble in ether, disulphide of 

 carbon, and chloroform. The solution of iodine in alcohol or ether 

 has a brown, the solution in disulphide of carbon or in chloroform a 

 violet, color. Iodine stains the skin brown, and when taken inter- 

 nally acts as an irritant poison. 



Tincture of iodine, Tinctura iodi, is a dark reddish-brown solution 

 of 70 grammes of iodine and 50 grammes of potassium iodide in 

 enough alcohol to make 1000 c.c. of solution. 



The increased solubility of iodine in solutions of iodides, or of 

 hydriodic acid, is due to the formation of definite compounds by a re- 

 versible action, thus, 



KI + 21 ^ KI 3 . 



The brown color of solutions of iodine in certain solvents, as alcohol, 

 ether, etc., has been shown to be due to a feeble combination between 

 one molecule of iodine and one molecule of the solvent. In violet- 

 colored solutions there is no combination. 



Iodine in very small quantity is a constituent of the human body and that 

 of animals. The greatest portion is found in the thyroid gland, as a complex 

 16 



