Zinc. 317 



with the afliftance of heat and boil away the 

 acid to drynefs. Repeat this operation twice 

 or thrice, ufing each time twice as much of 

 the acid as the ore weighs ; and, laftly, dif- 

 folve all that is foluble in a frefh portion of 

 nitrous acid : by this means the zinc (and 

 lead if any) with the argill, will be taken 

 up, while the iron, being dephlogifticated, 

 will with the filex remain undiffolved ; if 

 the folution contains lead, the marine acid 

 will precipitate it ; after which the vitriolic 

 may be ufed to precipitate the calcareous 

 earth, if any be contained in the ore, or the 

 lead and other metals may be precipitated by 

 adding a piece of zinc as in N? 9. The zinc 

 may then be precipitated by the Pruffian 

 alkali, the weight of which divided by 5 gives 

 that of zinc in its metallic form contained in 

 the ore. The undiflblved refiduum fliould be 

 treated with three times its weight of concen- 

 trated vitriolic acid, and evaporated to drynefs, 

 and all that is foluble extracted with warm 

 water ; the iron fhould be precipitated by the 

 PruJJlan alkali, arid the argill by the aerated 

 mineral alkali, which fhould alfo be added to 

 the nitrous folution after the zinc is preci- 

 pitated. 



1 1. Thefecond method is fhorter and more 

 ingenious. He diftills the vitriolic acid over 

 calamine to drynefs; the refiduum he lixi* 



viates 



