of Copper and of Iron. 217 



ality of which we can as yet, but in a few inflances, be fnre 

 we have attained. For every obfervalion, however trivial^ of 

 this kind, will haften the arrival of that moment when we 

 fhail be enabled to approach a little nearer to truth. 



I have, for many reafons, preferred boiling the nitrite of 

 copper with either of the fixed alkalis^ to the method gene- 

 rally recommended, which is, to precipitate all the copper 

 from its folvent, by carbonate of potafli or of foda; then, to 

 redinblve in muriatic acid ; and to precipitate, in the me- 

 tallic ftate, by a plate of polifiied iron. 



Firft, when an alkaline carbonate is ufed, the precipitate 

 is a carbonate of hydrate of copper; and this fubftance is fo- 

 lublc in an excefs of the precipitant. 1 once evaporated feme 

 very beautiful blue liquor, obtained in an operation of this 

 kind, and found a cryftallized fait, which I became defirous 

 to examine. But, as the folution contained another fait, 

 formed by the acid (which originally held the copper in fo- 

 lution) and the alkali employed, I found it neceflary to form 

 feme hydrate of copper dire6lly for the purpofe. 



Some hydrate of copper was therefore prepared, by decom- 

 pofing the nitrate of that metal by a very dilute folution of 

 potafh, and well wafhing and drying the precipitate : it was 

 that fine powder formerly well known a? the oxide of copper. 

 Some of this fubitance was thrown into a folution of car- 

 bonate of potafli, through which a current of carbonic acid 

 had been made to pais lor a long time, and thcv were then 

 (lightly heated together. One part of the hydrate became 

 of the fame colour as the real oxide ; the other was diffolved, 

 and the liquor was converted into a greenifli blue (olution. 

 Thus, one part of the hydrate had yielded its water to the 

 other, in order to favour this quadruple, or rather this double 

 combination, of carbonate of potafli and hydrate of copper: 

 the liquor, when reduced, aflbrdcd a mafs, which, repeatedly 

 rcdifl'olved and evaporated, with difficulty aflumed any deter- 

 minate form of crylhillization. This fait is a carbonate 

 of potafli, holding a litile copper. It is of a pale blue, and 

 varies in colour according to the quantity of water of cryf- 

 tallization, and of metal. It is flightly dcliquefcent, and 

 foluble in about three parts of water, at 60', but requires 

 much Icfs water when the water is boiling. It cryflallizcs 

 by cooling, much like carbonate of potafli. It is foluble in 

 a large quant'ty of alcohol. It loles about 43 per cent, of 

 carbonic acid, by folution in a (ironger acid ; and, prepared 

 in the manner I have mentioned, contains no more than 

 5 percent, of oxide of copper; although carbonate of potafli, 

 .' '(Cn poured iulo a folution of any lalt of copper, appears 



tu 



