ai6 ESSAYS and OBSERVATIONS 



large proportion of a diflblved fixed alkali, 

 the fedative fait gradually difappears, and is 

 United to the alkali without any efFervef- 

 cence 5 but if the addition be repeated 

 feveral times, it will at lafl be accompanied 

 with a brifk efFervefcence, which will be- 

 come more and more remarkable, until the 

 alkali be entirely faturated with the fedative 

 fait. 



This phanome?ton may be explained by 

 conlidering the fixed alkalis as not perfedily 

 faturated with air : and the fuppofition will 

 appear very reafonable, when we recolledt, 

 that thofe falts are never produced without 

 a confiderable degree of heat, which may 

 eafily be imagined to diffipate a fmall portion 

 of fo volatile a body as air. Now, if a fmall 

 quantity of the fedative fait be thrown into 

 an alkaline liquor, as it is very flowly dif- 

 folved by water, its particles are very gra- 

 dually mixed with the atoms of the alkali. 

 They are moft flrongly attraded by fuch of 

 thefe atoms as are deftitute of air, and 

 therefore join with them without producing 

 an effervefcence j or, if they expel a fmall 

 quantity of air from fome of the fait, this air 

 is at the fame time abforbed by fuch of the 



contiguous 



