136 A SYSTEM OF 



a. With the alcali of the common fait, or 

 fea-falt, Alcali miner ali fat uratum : Sal mi- 

 %abile Glauber*. 



This is a neutral fait, prepared by na- 

 ture, as well as by art, containing more 

 or lefs of iron, or of a calcareous earth, 

 from which arifes alfo fome difference in 

 its effects, when internally ufed. It moots 

 eafily into prifmatical criftals, which be- 

 come larger in proportion to the quantity 

 of water evaporated before the criftalli- 

 fotion. When laid on a piece of burning 

 charcoal, or elfe burnt with a phlogifton, 

 the vitriolic acid difcovers itfelf by the 

 frnell like to the he-par fulphuris. 



It is found in a diffolved flate in fprings 

 and wells, and in a dry form on wails, in 

 iuch places where aphronitrum has efflo- 

 refced through them, and the vitriolic acid 

 has happened to be prefent; for inflance, 

 where marcafites are roafted in the open 

 air. This fait is often confounded with 

 the aphronitrum, or a pure mineral alcali ; 

 and a learned difpute once arofe, which of 

 thefe falts ought with the greatefl propriety 

 \o be called natron, Baurach veterum^ fat 

 mirahile, or Epfom fait *, whereas it might 

 eafily have been decided by chemical ex- 

 celebrated experiments of Lemery, arid others, demonftrate, 

 and from which c.aufe many volcanos and earthquakes may 

 perhaps be deduped. The puhis pyrcphorus is alfo made of 

 alum, intimately united with a phlogiftic fubftance ; in, 

 the preparing of which, they ought carefully to avoid that 

 any iron enters the mixture, becaufe the acid has too ftrong 

 an attraction to the iron, and cannot unite with the phlo- 

 gilton alone, which, however, is quite necciTary in this ope- 

 ration. 



periments, 



