3$ 8 Fixed Air from calcareous Earth. [Book V. 



4thly. Fixed air is alfo extricated in large quantities 

 by the action of acids on calcareous earth. 



Fill a phial or a glafs receiver with water, and in- 

 vert it (in the lame manner as clefcribed in the chapter 

 on dephlogifticated air) in a bafon half filled v.'ith wa- 

 ter. Then put fome chalk or marble grofsly pow- 

 dered into another bottle, fo as to fill about a fourth 

 or fch part of it, and pour water upon it until the 

 chalk is covered, then add fome vitriolic acid to 

 it, in quantity about the fourth or fifth part of 

 the water, and apply a cork with a tube as before 

 to the bottle, fo chat the extremity of the tube may 

 pafs through the water of the bafon into the neck of 

 the other bottle which is inverted in the water. The 

 mixture of chalk and oil of vitriol will then begin to 

 cffervefce, and heat is produced, which may be felt by 

 applying the hand to the outfide of the veffel. Fixed 

 air is copioufly emitted from this mixture, and, pafTmg 

 through the bent tube, will proceed into the bottle in- 

 verted in the water, and afcend to the top of it. By 

 thefe means the inverted bottle may be filled with fixed 

 air, and being corked under water, may be removed 

 from the baton and kept for ufe. 



5thly. Fixed air is alfo expelled in large quantities, 

 by the application of heat only, from lime, chalk, mag- 

 nefia, or alkaline bodies, in what is called their mild 

 ftate, oppofed to cauftic; and by the experiments 

 of Dr. Black it was .found that this fubftance con- 

 ftituted nearly one-third of the weight of thofe bodies. 

 The alkalies and calcareous earths have confequently 

 a very powerful attraction for this fluid in their cauftic 

 ftate ; and it is therefore eafily condenfed by agita* 

 tion with lime water, as has been already intimated. 



This gas was long known to miners by the name of 

 choakdamp, fo called from its fatal fuffocating effects; 



and 



