Regulus of Arfenic. 331 



100 parts of it contain 16 of fulphur; ni* 

 trous acid foon deftroys its rednefs, 



10. To analyfe thefe ores, they fhould be 

 digefted in marine acid, adding the nitrous 

 by degrees to help the folution ; the fulphur 

 will be found on the filter ; the arfenic will 

 remain in the folution, and may be precipi- 

 tated in its metallic form by zinc, adding 

 fpirit of wine to the folution. 2 Bergm. 442. 



SPECIES IV. 



Calx of Arfenic djffufed through Earths or 

 Stones. 



1 1 . Henckel mentions a grey or bluifh marl 

 in which this calx was found ; clay and cal- 

 careous ftones are alfo fometimes impregnated 

 with it $ it is difcovered either by the fmell 

 when laid on burning coals, or by lixiviation. 



12. In the dry 'way calx of arfenic isfepa- 

 rated from the ores which contain it by fub- 

 limation in a well luted retort, and a gradual 

 heat, but fome always remains, which cannot 

 be expelled but by an open fire and the addi- 

 tion of charcoal. 



13. White arfenic, that is, calx of arfenic, 

 is reduced to a regulus, either by quickly 

 melting it with a mixture of 2 parts foft 



foap, 



