Muriate of Soda, or Common Salt

Found in abundance at Northwich in Cheshire, where it constitutes very solid strata, more or less mixed with common clay, giving it a dirty hue, or with yellowish or red calx of iron. Its large square crystals are often so transparent and clean as to appear uncontaminated. The miners leave pillars of it to support the roof; and when they show this crotto, they are proud to surprise the spectators, and add lustre to the scene by the display of many lights.

The middle figure shows the fracture to be cubic, and also some clear pieces lying among the coloured kind. I have none approaching the octaëdron or the cubico-octaëdron, see Haüy; nor do I know that it is found so in Great Britain.

Salt in sufficient quantity preserves animal substances from putrefaction, but too little is said to promote it.

Lustre 2 or 3, glassy. Transparency 2, 3, or 4. Hardness 4, 5, or 8. Spec. grav. 2,143. Brisson. Soluble in little less than 3 times its weight of water, at the temprature of 60. Kirw. Refraction single. Salt in the artificial way of preparing it, if crystallized hastily for use, has the centres of the cubes concave, or depressed, as it were, step by step from the edges, forming a curious figure. This is not uncommon in what is called rock salt; so called from being sold in fine grains, and pressed into conical baskets. Common salt is also used for glazing common earthen ware. 100 parts of this salt contain 35 of soda, and nearly 40 of muriatic acid, the rest being water. Kirw. 2. 33. Soda is an ingredient best procured from common salt. It is otherwise procured from sea plants. Soda not being found native in Great Britain, I take occasion to speak of it in this place. It is useful in making glass, and has lately been much used in common washing; often indeed so indiscreetly as to rot the linen, and even to act as Hercules’s poisoned shirt, particularly to the tender skin of infants. Mothers will do well to be assured of their linen being well rinsed in plenty of cold water.

Fibrous salt may be found of different shades of white, red, or brown, depending either on a common clay, or on oxide of iron. This specimen has a piece or two of common clay in the centre. Its fibrous part is coloured by a red oxide of iron. This sort of specimen has been compared to wood, the curvature of the fibres and the fracture corresponding to that fanciful idea. Some have thought the red kind here figured resembled muscular fibres.