iv CHALK; LIME, AND THE ALKALIS 57 



their forces unimpaired, as takes place when sal ammoniac 

 .... is distilled with salt of tartar [i.e., potash] (A. C. R. 

 XVII. 160). 



When sal ammoniac is acted on by lime a pungent gas 

 is liberated, to which, at a comparatively late date, the 

 name of AMMONIA was given. During the alchemistic period 

 this pungent vapour was (like spirit of salt) known only in 

 the form of a solution which was called the VOLATILE SPIRIT 

 OF SAL AMMONIAC. It was also prepared by distilling horn, 

 and was therefore known as SPIRIT OF HARTSHORN. 1 

 Priestley, who was the first to collect spirit of salt as a gas 

 over mercury, was also the first to collect ammonia in the 

 gaseous state (see Chapter V). 



Black showed that the "mild spirit of sal ammoniac" 

 (described above as sal volatile) could be rendered caustic 

 by removing its fixed air with the help of magnesia; it 

 then "emitted a most intolerably pungent smell," effervesced 

 only slightly with acids, and produced only a turbidity 

 when mixed with lime-water. It was therefore evident that 

 the pungent gas was a caustic alkali which could be rendered 

 mild by union with fixed air. Final proof of these facts 

 was supplied when Priestley showed that gaseous ammonia 

 could be combined with fixed air to produce solid sal 

 volatile, whilst with gaseous spirit of salt it united to form 

 sal ammoniac. 



C. PREPARATION OF NEW EARTHS. 



Earths can be prepared from salts by the action of 

 alkalis. At the close of Chapter II it was shown how the 



1 "Of the spirit and oil of Harts-horn. Take Harts-horn, cut it 

 with a saw into pieces, of the bigness of a ringer, and cast in one at 

 a time into the aforesaid distilling vessel, and when the spirits are 

 settled, then another, and continue this until you have spirits enough : 

 and the vessel being filled with the pieces that were cast in, take them 

 out with the tongs, and cast in others, and do this as often as is 

 needful." (Glauber, Philosophical Furnaces, Part II. ; Works, I. 51) 



