THE ALKALIES. 139 



combination witli acids, act as powerful caustics when 

 applied to the flesh of animals, and are soluble in water 

 Potash and soda have been called fixed alkalies, because 

 they will endure a great heat without being volatilized : 

 and yet in a very high temperature they are dissipated in 

 vapour. They were formerly considered to be simple sub- 

 stances, but they are now found to be compounds of metallic 

 substances, called potassium and sodium, with oxygen. They 

 have various uses in surgery and medicine, and are employ- 

 ed in large quantities by the glass-maker, the dyer, the soap- 

 maker, the colour-maker, and by many other manufacturers. 

 Ammonia is so extremely volatile as to exhale at all known 

 temperatures. When combined with carbonic acid, it takes 

 a concrete form, and a beautiful white colour, and is known 

 in commerce by the name of volatile salts. With muriatic 

 acid it forms what is termed sal ammoniac, which is employ- 

 ed in many of our manufactories, particularly by dyers to 

 give a brightness to certain colours. In tinning metals it is 

 of use to cleanse the surfaces, and to prevent them from 

 oxydizing by the heat which is given to them in the opera- 

 tion. Ammonia is furnished from all animal substances by 

 decomposition. The horns of cattle, especially those of deer, 

 yield it in abundance, and it is from this circumstance that 

 a solution of ammonia in water has been called hartshorn. 



Questions. — 1. What are earths? 2. What the names of the 

 mne earths ? 3. What is said of silex ? 4. Of alumine ? 5. Of 

 lime ? 6. Of magnesia ? 7. How are alkahes distinguished ? 8. 

 Why are potash and soda called fixed alkalies ? 9. Of what are they 

 compounds ? 10. What is said of their uses ? 11. From what is am- 

 monia furnished .-" 12. What is said of its combinations and uses ? 

 [Note. Besides the nine earths, above enumerated, we have now 

 thorina, which is a rare earthy substance lately discovered. A new 

 alkali, called lithia, has recently been discovered, which, like potash 

 and soda, is found to be a metallic oxyd : its base is called lithium, 

 Three new vegetable alkalies have also been discovered, called mor- 

 phia, picrotoxino, and vauquelinc. Clay, as it exists in soils, is com- 

 monly called argillaceo'us earth ; and lime in soils is called calcar^- 

 0iis earth.] 



