$52 ALKALIES. 



7. Soda with oil forms hard soap potash soft; and soda is per- 

 haps a little less caustic than potassa. 



8. Distinctive characters. 



(a.) It forms different combinations with acids ; for instance, the 

 sulphate of soda is very soluble in water ; that of potash the opposite. 



(b.) Its salts, suspended upon platinum wire, impart a rich yellow 

 color to the blowpipe flame. Turner. 



(c.) Muriate of platinum and tartaric acid give no precipitates with 

 salts of soda : the opposite is true of potash. 



9. USES AND IMPORTANCE. Soda is scarcely inferior in this re- 

 spect to potassa : in soap and glass making it is largely used, and it is 

 preferred for the finest articles. In the form of carbonate it is much 

 used in medicine as an antacid : in medicine the caustic soda, is not 

 used, having no advantage over potash. 



10. The distinction of vegetable and mineral* alkali is unfounded; 

 for both are found in plants, and both also in stones and various min- 

 erals. Still it is true that potash is found in most plants, and soda in 

 those only which are connected with saline sources ; on the other 

 hand, solid mineral salt, the ocean and other saline waters, and the 

 soda lakes and incrustations, present great quantities of that alkali in 

 the mineral kingdom. f 



11. POLARITY. In the galvanic circuit, soda goes to the negative 

 pole, and is therefore electro-positive. Its combining weight is 32. 



REMARKS. In commerce, we never see caustic soda ; in its pur- 

 est form, in the shops, it is always in semi-crystalline masses of car- 

 bonate, called sal soda. 



The purest fossil alkali, obtained from the efflorvescence on plaster 

 walls, contains about 60 J of its weight of alkali in crystals. 



Alkali manufactured at Liverpool, - 49 



Fossil alkali from India, - 28 



Best Alicant Barilla, - 26 J 



Sicilian Barilla, - 23 



The richest Kelp, made in Norway, the Orkney Islands, 



and Skye, 6 



The general produce of Scottish Kelp, - 2J 



There are associated with the soda in sea-weed, muriate and sul- 

 phate of soda, hydriodate of potash, or soda, and portions of lime, 

 magnesia, silica, and alumina. There is also more or less of sul- 



* Potash was formerly culled the vegetable alkali, and soda the mineral. 



t As felspar, which constitutes so large a proportion of granite, whose detritus 

 forms a considerable part, oi our soils, contains, on an average, at least 10 per cent, of 

 potassa, this alkali may after all be more abundant than soda. J. T. and C. U. S. 



t Black's Lect. 



