[1213] Lib. xxx. 7.
[1214] This is particularly the case in regard to Aristot. Auscult. Mirab., as I have remarked in the preface to my edition.
[1215] In the island of Dagebull, and also in Faretoft and Galmesbull, Frisio salt is made in the following manner. The inhabitants proceed along the coast in small vessels, and at low water go on shore on the mud, which they dig up till they come to a kind of earth called torricht; it is of a turfy nature, and interwoven with roots. This earth they convey to the islands, where they spread it out in the sun and leave it to dry, after which it is formed into a heap and burnt to ashes. What remains is again spread out, moistened and trod upon with the naked feet; the small stones and other useless parts are picked out, and being again dried and besprinkled with water, the ley is put into salt-pans and boiled into salt.
[1216] Mémoires de l’Acad. de Bruxelles, 1777, i. p. 345.
[1217] Elementa Chemiæ. Lugd. Bat. 1732, 4to, i. p. 767.
[1218] Boyle considered the words of Solomon as a proof that nether must be fixed alkali; and he was the more convinced of it when he saw nitre obtained from Egypt effervesce with acids.
[1219] See the [History of Soap] in vol. i.
[1220] Plin. xxxvi. 26, § 65. The use of nitrum in making glass is often mentioned.
[1221] Plin. xxxi. 10.
[1222] Lib. xxx. 10.