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CHAPTER XV. 



ALKALIS. 

 ALKALI SODA BARILLA KELP. 



ALKALI is a term derived from kali, the Arabic name 

 of a particular plant, from which, probably, an 

 alkaline substance was first extracted. Its principal 

 characteristic is that of combining with acids, to 

 neutralize their activity, arid produce neutral salts. 

 It has likewise a great affinity for animal and vege- 

 table oils, with which it unites and forms soap. Alkali 

 is of most extensive utility in many manufactories. 

 Itself an opaque substance, it combines with sand, 

 which is also opaque, and from this union results 

 perfectly transparent glass ; a substance which, when 

 considered with reference to all its various qualities, 

 may be termed the most beautiful and the most won- 

 derful production of the art of man. 



The hue of most colours is altered by the addition 

 of alkali, and it is therefore much employed in the 

 different processes of dyeing. In bleaching, in calico 

 printing, and in many other useful arts, it likewise 

 holds an important place. 



There is no doubt that the method of obtaining 

 the alkalis from vegetable substances must have 

 been known and practised by the Romans. A de- 

 cisive proof of this was found among the ruins of 

 Pompeii, in which a soap-boiler's shop was disco- 

 vered, containing a quantity of soap which had 

 evidently been composed of oil and an alkali. This 

 soap has been described by those who have seen 



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