IODINE.
Ill
tera marina, and, more recently, in two growing in Mexico ; namely, a spe-cies of Agave and a species of Salsola — (Journ. Pharm. tom. xxiii. p. 31.)
Preparation. —Iodine is obtained from the Fucoidea (one of the divi-sions of the family Alga ). The plants of this tribe, by combustion, yieldan ash or cinder, commonly denominated kelp, which contains iodine.Davy states that French kelp is more productive than British; andEklond, from experiments made at the Cape of Good Hope , concludesthat the Laminaria buccinalis yields more than any European Alga.
Kelp is a very heterogeneous substance. Its soluble parts are thechlorides of sodium and potassium, carbonate of soda, sulphates of sodaand potash, and the sulphuret and iodide of potassium or of sodium.To these must be added a small quantity of alkaline bromide. The quan-tity of iodide, however, is very small in comparison with some of theother salts, and, therefore, the first object in the manufacture of iodine isto separate as much of these as possible. By repeated crystallizationswe readily attain this, since the iodide being very soluble is left in themother liquor, along with the sulphuret and a portion of the other salts.
This liquor is introduced into a stoneware still, sulphuric acid and thebinoxide of manganese are added, and heat applied. Iodine distilsover, and after being washed with water, is dried between folds of bibu-lous paper.
In this process two equivalents, or 80 parts of sulphuric acid, react onone equivalent, or 44 parts of binoxide of manganese, and on one equiva-lent, or 166 parts of iodide of potassium, and yield one equivalent, or 126parts of iodine, one equivalent, or 88 parts of sulphate of potash, and oneequivalent, or 76 parts of the sulphate of the protoxide of manganese.
INGREDIENTS USED.
PRODUCTS.
leq.IodidePotas m .166 jleq.Binox.Mangan.44 ^2eq. Sulph c . Acid 80 ^
1 eq. Iodine ....1 eq. Potassium . .1 eq. Oxygen . . .1 eq. Protox. Mang.1 eq. SulphuricAcid.1 eq. SulphuricAcid.
126_
^8 j l ec L*P° th *48..36"
40.
40-
1 eq. Sulph te . Potash . 881 eq. Protosulph te . Mang. 76
Bussy {Journ. Pharm. t. 23, p. 17) has proposed another mode of pro-curing iodine.
Properties. —Iodine is a crystallizable solid, its primary form being arhombic octahedron. It is usually met with in micaceous, soft, friablescales, having a greyish black colour, a metallic lustre, an acrid hot taste,and a disagreeable odour somewhat similar to that of chlorine. It fusesat about 225° F., and at 347° is volatilized, though the vapour rises alongwith that of water at 212°. Iodine vapour has a beautiful violet colour,and a great specific gravity; namely, 8'716, according to Dumas. Iodinerequires 7000 times its weight of water to dissolve, but alcohol and etherare much better solvents for it. Its atomic weight is about 126.
Characteristics. —In the free state iodine is distinguished from mostother bodies by its forming an intense blue colour with starch. So deli-cate is this test, that Stromeyer says, water which does not contain morethan one four-hundred-and-fifty thousandth of its weight of iodine, ac-quires a perceptibly blue tinge on the addition of starch. This bluecolour is destroyed by heat, and, therefore, in testing for iodine the liquidsemployed should be cold: an excess of alkali also destroys it by forming