Fossils. 157 



deliquescent, absorbs water with heat 

 and a peculiar faint smell, combines with 

 siliceous earth by fusion, and forms glass. 

 It is frequently found native with lime, 

 and combined with different acids ; but 

 is chiefly obtained from vegetables, in 

 the ashes of which it remains after com- 

 bustion. 



Soda or the mineral alkali, is procured 

 from the ashes of sea-weed, and consti- 

 tutes the basis of sea-salt. It strikingly 

 resembles potash in form, causticity, fusi- 

 bility, deliquescency, combination with 

 earthy substances, by means of fusion, 

 action on animal substances, Sec. so that 

 it was long confounded with it, and might 

 have continued to be so, if it did not form 

 very different salts with acids, and yields 

 these acids to potash. 



Ammonia, or volatile alkali, differs 

 greatly from the two preceding species 

 in its form of gas when dissolved in cal- 

 coric, in its liquid form when dissolved in 

 water, in its pungent and suffocating 

 smell, its solubility in air, &c. Am- 

 monia is procured by burning animal 

 substances ; in Egypt, (from whence, as 

 contained in sal ammoniac we till of late 



