Page:Popular Science Monthly Volume 36.djvu/395

Rh combustion are lost and the escaped gases overcloud whole townships, and impart to miles of sea-shore the peculiar odor characteristic of burning kelp. To save these gaseous products by distilling the weeds in closed retorts, at low temperatures, would mean the production, at little extra cost, of valuable amounts of ammonia, parafin, acetic acid, naphtha, etc. In addition, the charcoal left would be much richer in iodine than the ordinary kelp, and its mechanical form much easier of subsequent extraction. Attention has been called time and again to the enormous waste of material and the easy means of improvement in kelp-making, but thus far little inroad has been made into this European species of ancestor-worship. The crofters cling to traditional methods and primitive tools.

When kelp, such as has been described, is brought into market, it is purchased by those directly engaged in making the salts of iodine and the alkalies. In their hands it becomes the subject of careful treatment to separate the valuable ingredients from the gross impurities with which they are associated. This is commonly done by breaking the kelp into small lumps and lixiviating in suitable vats filled with hot water or supplied with steam vapor. Such treatment, when sufficiently prolonged, dissolves out the alkaline and iodine salts, which need only the subsequent operation of being allowed to settle and siphoning off to separate them from the insoluble matters. The liquor contains chiefly the chlorides, the sulphates, the sulphites, and the hyposulphites of sodium and potassium, as well as the iodides and bromides of those metals. By evaporating this solution, the greater portion of the chlorides and sulphates will crystallize out before the iodides, bromides, and lower sulphur compounds begin to deposit. The former may then be fished out of the evaporating pan, leaving a resultant mother-liquor rich in iodides. The hurtful sulphur compounds remaining are decomposed by excess of strong sulphuric acid, and then the proper quantity of manganese dioxide is added. This mixture is transferred to an iron retort and heated, the result of which is to liberate the iodine and part of the bromine present. The vapors of these elements are conducted into proper earthenware condensers, where the iodine is deposited as a black powder, and the small quantity of bromine as a dense brown liquid moistening the iodine powder. As before indicated, from twelve to twenty pounds of this crude iodine are obtained from the mother liquor of one ton of kelp. There are several possible ways of purifying the crude iodine, in order to secure the iodine of commerce and also the bromine which had been its chief impurity. Even this purified iodine contains minute traces of bromine, owing to the difficulty of their perfect separation. If iodide of potassium is desired instead of free iodine, it is still necessary to produce