1835.] Analysis of Nellore Copper ores. 579 



equal weight, this operation affords no test of the quantity of sulphur 

 present. — In fact, not expecting from Dr. Thomson's analysis, to find 

 sulphur in the Nellore copper ore, I at first neglected the precautions 

 necessary for its separation. This was accordingly effected on other 

 samples, by boiling in strong nitric acid, which, from its heat, caused 

 part of the sulphur in a pure state to rise in fused globules to the 

 surface : while a portion, being oxygenated, was afterwards separated 

 by precipitation with barytes. 



The quantity of copper was most conveniently estimated from the 

 black oxide taken up from the calx by dilute nitric acid. It was also 

 obtained directly from other samples by reduction of the oxide with 

 charcoal and borax. — The iron and pyrites were deduced from the 

 difference between the residue in the cold solution, and that from the 

 hot dissolution in strong acid of another parcel, before calcination. 



Collecting together the results of the above operations, we have 



the following data, whence to deduce the composition of the three 



specimens. 



No. I. No. 2. No. 3. 



a. Loss of carbonic acid by digestion in dilute nitric 



acid 12.0 14.6 7.0 



b. Loss of water (and some carb. acid ?) by heating 



without air in a glass tube, 5.0 7.0 3.0 



c. Total loss on calcination with access of air, 17.5 17.8 21.0 



c2. Ditto average of two other trials (more carbonate,) 20.0 20.3 23.5 



d. Oxide of copper taken up from calx c by dilute acid, 37.7 49.2 73.7 



e. Residue of insoluble earths and ox. iron, after d, 44.8 33.0 5.3* 



f. Residue from digestion of crude ore in boiling nitric 



acid, 20.0 13.9 19.0 



g. The same, after burning off the sulphur and redi- 



gesting in do 20.0? 8.5 0.0 



h. Sulphur, separated on boiling in strong acid, ..... 0.6 2.1 9.0 



i. Sulphate of barytes precipitated afterwards, 1.4 17.8 28.5 



k. Weight of metallic copper actually recovered from e 2, 28.5 52.2 59.0 



In regard to d, No. 3, it was observed on digestion in cold nitric 

 acid, that a very considerable portion of the calx of copper was of a 

 red color, or in the state of protoxide, or perhaps in a metallic state, 

 and was not taken up without disengagement of nitrous gas ; — the 

 weight 73.7 must therefore be increased, to give the true weight in 

 terms of the peroxide. This is also proved by the amount of loss in 

 c, 21.0, which is considerably in excess; and it was remarked on 

 removing the calx from the fire that it was agglutinated, so as per- 



* This residue may have consisted partly of sulphuret of copper that had 

 escaped decomposition in the fire ; for another specimen was wholly soluble, and 

 little iron was present in the solution. 



