CARBONATE OF SODA. 105 



powder-makers. When first imported its price was 

 low, and it was accordingly advantageously substi- 

 tuted for the more expensive nitrate of potash in the 

 manufacture of nitric acid ; but as the price of nitrate 

 of soda soon rose, it was no longer found profitable 

 to use it for this manufacture, and now almost the 

 only purpose for which it is employed is as a manure. 

 It appears to resemble the nitrate of potash in its 

 effects on growing plants, and like it to exert con- 

 siderable influence on the fertility of certain kinds of 

 land (901). 



218. The " soda" of commerce is, as will be 

 readily supposed, not the pure alkali soda, but is a 

 carbonate, and, like the carbonate of potash, pos- 

 sessed of considerable caustic properties. It was 

 formerly for the most part procured by burning sea- 

 weed, the ashes of which contain a large quantity of 

 carbonate of soda, and immense quantities of sea- 

 weed were annually collected and burnt, for the pur- 

 pose of obtaining weed-ash, kelp, or barilla, as the 

 crude salt was called. 



219. Of late years, however, means have been 

 discovered of obtaining the carbonate of soda by de- 

 composing common salt ; from which it is now manu- 

 factured so cheaply that it has not only superseded 

 the use of kelp or barilla for all purposes where car- 

 bonate of soda is required, but has also from its low 

 cost been substituted to a great extent for potash 

 and pearlash ; and hence the carbonate of soda, or 

 "soda/' as it is commonly called, is very largely used 



