‘ats 
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| PHYSICAL anv LITERARY. 203 
expell it entirely from fixed alkalis, or 
take away their power of effervefcing with 
acid falts. ; 
THEsE confiderations led me to cons 
clude, that the relations between fixed air 
and alkaline fubftances was fomewhat fi- 
moilar tothe relation between thefe and a- 
cids; that as the calcarious earths and al- 
kalis attract acids ftrongly and can be fa- 
turated with them, fo they alfo attract fix- 
ed air, and are in their ordinary ftate fa- 
turated with it; and, when we mix an a- 
cid with an alkali or with an abforbent’ 
earth, that the air is then fet at liberty, 
and breaks out with violence; becaufe the 
alkaline body attracts it more weakly than 
it does the acid, and becaufe the acid and 
air cannot both be joined to the fame bo- 
dy at the fame time. 
I alfo imagined, that, when the calca- 
rious earths are expofed to the ation of a 
, Violent fire, and are thereby converted in- 
"to quick-lime, they fuffer no other change 
Bip. their compofition than the lofs of a 
{mall quantity of water and of their fixed 
air. ‘The remarkable acrimony which we 
: perceive 
