of Copper and of ' Pon. 221 



When copper and iron arc to be fcparated, one fingle aSu- 

 fion of ammonia will not always fuffice. Tliat two^'may be 

 fonietimes ncccOary, is an objecliou to the method I propofe 

 for the fubfcquent cbiiliilion with potafli. But, when I ufe 

 that of precipitating the copper by iron, it requires no pre- 

 vious precipitation by any alkali. It is fufficient to add mu- 

 riatic acid to the original folution of the ore in nitric acid, 

 and evaporate to drynel's. The nitric acid is diflodged from 

 the oxide of copper, and the muriatic takes its place. If a 

 finglc evaporation is not fufficient, a fecond (for tne operation 

 is very (hort, and caufes no lofs upon iihers, &.c.) r.iay he 

 attempted; and when the iron ufed for the purpofe of re- 

 vivifying the copper is put in, the liquor mav be made to 

 boil; by which nie;^ns the procefs is rendered much moi-e 

 certain and expeditious. Some iron will necclTIirily be dif- 

 folved, and the quantity mu(l be noted. The liquor, which 

 contained muriate of copper and of iron, now contains onlv 

 the latter. Boiled with a little nitric acid, it will become 

 red; and then ammonia, or potafli, will give a red precipi- 

 tate, which, well waflied and dried, will reprefent 6l per 

 cent, of metallic iron. All thefe metals having thus been 

 precipitated, no conftitucnt part of the ore, except the ful- 

 phur, which, in the iirft treatment, had been converted into 

 fulphuric acid, is contained in the liquor; and from it, when 

 neutralized, this latter may be precipitated by nitrate of ba- 

 rytes, which will reprefent 14,6 per cent, of fulphur. The 

 abfolute ncccllity of conftantly ufing pure alkalis, in this 

 method of analylis, is too evident to be inlilted upon. 



GENERAI, VIEW OF THE FOREGOIXG ANALYSES. 



Tn taking a retrofpeftive furvcy of the experiments above 

 related, upon the various natural arfeniates of copper which 

 we have examined, wc fliali find, 



Fird, That natural artcniate of copper exifts in three dif- 

 ferent Itates of combination ; the firli containing 14 jx-r cent., 

 the fecond 31 per cent., and the third about 29 per cent, oif 

 acid. 



Secondly, That each of ihcfc may contain difierent propor- 

 tions of water, cither as conftitutin'g a hydrate, or as water 

 of cryftallizatioii. 



Thirdly, Tliat, upon lofing its water, a rfeni arte of copper 

 will pafs from blue to pale trreen, and finally to brown, as iii 

 No. I. ' ' 



iMHirtfjly, That No. I. is the only real arfeniate of copper, 

 all the others being arfeniates of liydratc of copper. 



J'lltlily, That No. I. is not to be admitted as an arfeniate 



of 



