258 VEGETABLE SUBSTANCES, 



it as being still perfect, though more than seventeen 

 hundred years must have elapsed since it was ma- 

 nufactured. 



Potash and pearlash, which contain potass and 

 barilla and kelp, which contain soda are the alkalis 

 known in commerce and used in the arts. These are 

 both obtained by the incineration of vegetables. 

 Soda is produced from the ashes of marine plants, 

 which growing chiefly in salt marshes, or on the sea- 

 shore, are supposed to imbibe and to decompose the 

 marine salt, separating it from its acid, partly by the 

 power of vegetation in the plant itself, and partly 

 by the burning. 



Soda, moreover, is contained abundantly in many 

 other situations ; it is the base of sea-salt, which is 

 found in immense masses under the earth's surface 

 in many countries, particularly in Poland, Hungary, 

 Spain, and England. 



Soda is likewise found combined with carbonic 

 acid gas in abundant quantities, in the natron lakes 

 of Egypt, in the East Indies, and in various other 

 countries. In summer, the water of the lakes being 

 evaporated, a bed of natron or carbonate of soda is 

 jeft generally two feet thick ; this is broken up by 

 wedges, and packed for the European markets. 

 Natron is brought in large quantities from China and 

 other parts of the east. 



The two alkalis, potass and soda, are very similar in 

 their general properties, though the variety of salts 

 which they form in combination with the acids, 

 generally exhibit a marked difference. Potass is 

 more deliquescent than soda, that is, it dissolves 

 more readily by the action of the atmosphere ; it is 

 likewise more acrid, and for this reason soda is pre- 

 ferred in most manufactories, as it does less injury 

 to fibrous fabrics, and does not corrode or destroy in 

 an equal degree the utensils used in its application. 



