3c6 Anahfis of the Arfen'uites 



in that ftate it was fnflered to remain three days, daring 

 which time the bottle was frequently ihaken. The acid be- 

 came at firft of a light blue, and incrrafed in colour by re- 

 maining upon the ore. At the expiration of the above term, 

 the liquor was decanted ; the refiduum was well waflicd and 

 dried, and weighed 42. The blue liquor contained merely 

 common phofphate of copper, held in folution by an excefi 

 ot acid. Ui)t)n the 42 parts of refiduum, llrong mmiatic acid 

 was poured, which did not appear to produce the fmallell 

 change or eiVect. It was evident, therefore, that fome pre- 

 vious alteration had been produced ; for, if it had remained 

 in its original Hate, muriatic acid would have aded upon it, 

 as in I he cafe already mentioned. To operate more effeolu- 

 Hily, nitric acid was added, and the whole gently heated. 

 A complete loKuiou followed, during which much nitrous 

 gas was difengaged. The remainder of the nitric acid was 

 expelled by evaporation ; and a plate of poliOied iron, im- 

 nierfed in this muriate of copper, afforded a precipitate of 

 metallic copper, weighing within one part as much as the 

 weight (>f the lirft reliduum. It was evident, therefore, that 

 a partial rcduftion of the ore had taken place; and, what is 

 flill more (irange, had taken place by means of the prefence 

 of an acid. 



In many obfervations which have prefentcd themfelves in 

 the courle of various analytic experiments, ibmething fimiiar 

 had before occurred to me. I have known metallic oxides 

 yield a part of their oxygen, one to the ot'.ier, in favour of 

 fome particular folvent.' When the metallic oxide A, for 

 inftance, containing 25 per cent, of oxygen, is in contaft 

 with ihc metallic oxide /J, containing 10 per cent, they will 

 each remain quiefcent in their rei'pec1;ive itates. But, if the 

 folvent C comes to be added, and if the fubrtance £-, at 10 

 per cent, of oxygen, lias no affinity for C, but at 15 or 20 

 per cent, has a very powerful affinity for it, then may the 

 oxide A lend a part of its oxygen, in order to favour the com- 

 bination of B, at 15 or 20 per cent, with the folvent C. In- 

 deed, as loon as I law the phol'phoric acid alTume gradually 

 a blue lingc, and the undiifolvcd powder begin to wear a 

 more brilliant appearance, I imagined [ fliould not fail to 

 recognize the fame Wxtl \\\ tliis cafe. When phofphoric acid 

 has remained long enough upon the pulverized ore toditfolve 

 all It can, the oxygen is concentrated, as it were, to the 

 amount of 20 per cent, in the part which is dilfolved ; and 

 all that whic<li could not be difliilvcd has (through the two- 

 fold affinity of copper for oxygen, to tlie ainount of 20 per 

 ?ent. aadof phoiphuric acid for that oxide of copper, at tliat 



dejiree 



