108 On the Extraction of Salts from Sea-Water. 



trading soda fVom sea-salt. Obliged for the purposes of war to 

 employ all the potash, which the country could produce, for the 

 manufacture of saltpetre, it became necessary for the fabrication 

 of soaps and glass to replace this alkali by soda, and. therefore to 

 devise some more abundant source of it than was afforded by sea- 

 weed. It was. then that the Government having offered a prize 

 for the most advantageous method of extracting the soda from 

 sea-salt, Leblanc proposed the process above alluded to, which 

 consists in converting the chlorid of sodium into sulphate, and 

 decomposing this salt by calcining it with a proper mixture of 

 ground limestone and coal, thus producing carbonate of soda and 

 an insoluble oxy-sulphuret of calcium. This remarkable process, 

 perfect from its infancy, has now been adopted throughout the 

 world, " and those who thought to annihilate the industry of 

 France were soon obliged to borrow from her, those great resources 

 which French science had invented." (Payem, Chimie Industri- 

 elle, p. 209.) 



Soda has now replaced potash to a very great extent in all 

 those arts where it can without prejudice be substituted for the 

 latter ; potash is however indispensable for the manufacture of 

 fine crystal and Bohemian glass, for the fabrication of saltpetre, 

 as well as for the preparation of various other salts employed in 

 %e arts. The country people in France having been accustomed 

 to employ the crude American potash for the bleaching of linen, 

 were unwilling to make use of the purer soda-ash, and the result 

 is that a great part of what is sold as American potash in France, 

 is nothing more than an impure caustic soda, coloured red with 

 sub-oxyd of copper, and fused with an admixture of common salt, 

 which serves to reduce its strength, and give it the aspect of the 

 crude potash of this country. 



But notwithstanding the soda from sea-salt is now replacing 

 potash to so large an extent, the supply of this alkali is scarcely 

 adequate to the demand, and the consequence is that while the 

 price of soda has greatly diminished, that of potash has of late 

 years considerably augmented, and it has even been proposed to 

 extract this alkali from feldspar and granitic rocks, by processes 

 which can hardly prove remunerative. The rapid destruction of the 

 forests before the advancing colonization of this continent, threat- 

 ens at no distant clay to diminish greatly the supplies of this as 

 yet important production of our country, and it was therefore a 

 problem of no small importance for the industrial science of the 



