52 



00. Kirw. Refraction single. Salt in the artificial way of pre- 

 paring 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 un- 

 common in what is called rock salt, which is often brought 

 to our tables in preference to basket salt ; so called from being 

 sold in fine grains, and pressed into conical baskets. Com- 

 mon 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, particu- 

 larly to the tender skin of infants. Mothers will do well 

 to be assured of their linen being well rinsed in plenty of 

 cold water. 



TAB. XXII, Lower Figure. 



SODA fibrosa. 



Fibrous Muriate of Soda. 



Div. 2. Imitative. 



Fibrous salt may be found of different shades of white, 

 red, or brown, depending either en 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 10 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. 



