342 ESSAYS AND OBSERVATIONS 



drawing ofF part of the folvent liquor by 

 evaporation or diilillation, the difTolved 

 body falls down gradually in proportion 

 to the quantity of the liquor wafted. 



I fliall chiefly confider the firft or more 

 proper precipitation, in which there is 

 both greater variety, and more difficulty 

 to account for a change. 



Remark I. All precipitations do not 

 happen from the oppofition of an alcali to 

 an acid ; but there are different means of 

 precipitating different folutions. 



It is certain, from experience, that 

 whatever bodies are capable of being 

 diflblved in any acid liquor, may be pre- 

 cipitated from it by an alcaline fait or 

 liquor. On the other hand, any body 

 that is difTolved in an alcaline liquor may 

 be parted from it by the addition of an 

 acid. This then is a pretty general me- 

 thod of precipitating : However this op- 

 pofition of acid and alcali is not the fole 

 caufe of precipitation ; for many metals' 

 and metallic fubftances, diflblved in their 

 proper acid menftrua, may be precipita- 

 ted 



