Algin. On the surface of certain species of seaweed—notably of those belonging to the genus Laminaria—there is sometimes seen a jelly-like material, which is partly formed of a substance called algin, and may be drawn out by the fingers in long tenacious strings. The cell-walls of our common brown seaweeds (Fucus and Laminaria) are, in fact, very mucilaginous, and all contain algin, which has somewhat remarkable properties. This substance was discovered in 1881 by Mr E. C. C. Stanford of Glasgow. If the leaf-like thalli of a Laminaria are immersed in water containing a little carbonate of soda, the whole cellular fabric of the plant becomes broken up in the course of twenty-four hours, forming a thick gelatinous mass containing about 2 per cent. of algin. This mass, after being cautiously heated, is filtered through coarse linen, and the cellulose which is left behind amounts, when dry, to from 10 to 15 per cent. of the air-dried plant. The solution which passes through the filter contains, in addition to the algin in the form of alginate of soda, some mucilage and dextrine. When sulphuric or hydrochloric acid is added, the algin, or, more correctly speaking, the alginic acid, separates in flocks, and is easily washed and pressed in a filter-press. In this condition it forms a compact cake not unlike new cheese. Chemically, it is a nitrogenous organic acid, and is the insoluble form of algin. When required for use in a soluble state, it is redissolved to saturation in solution of carbonate of soda, when alginate of soda is again formed.
The properties of algin in the soluble form are those of a very viscous gum, drying up to a transparent elastic film. As a size or dressing for textile fabrics, experiments have shown that algin goes further and does more work than starch or any of the ordinary gums, and it has the advantage of being easily rendered insoluble in water. Algin makes an excellent thickening for soups, and with the addition of a little gelatine or isinglass, is serviceable for jellies. The insoluble form of algin, in the dry state, resembles horn, and can be turned and polished. Different compounds of algin are now being experimented with for various other purposes in the arts.