Note 20 — Chapter XII
Reading edition
The manner of extracting potash from sea-weed is as follows:—When a sufficient quantity of kelp has been collected, it is spread out in a place where it will be dried by the sun and wind, and when dry enough to burn, a hollow is dug in the ground three or four feet wide; round its margin are laid stones, on which the weed is placed and set on fire. Quantities of this fuel being continually heaped upon the circle, there is in the centre a constant flame, from which a liquid substance, like melted metal, drops into the hollow beneath. This substance is worked, or stirred, with iron rakes, and brought to an uniform consistence while in a state of fusion; and when cool, it consolidates into a heavy, dark-coloured alkaline substance, which undergoes in the glass-houses a second vitrification, and then assumes a perfect transparency.