t$o Kcfear'chcs reftc&lng 



the muriate of Iron by potafli, retains part of the potaili* 

 Facts of this kind may be collected in great number. There 

 is no doubt, therefore, but that the observations which have 

 been made upon the precipitations of fubltanees which lofef 

 their folubiiity, cannot be applied to the metallic precipitates* 

 which vary according to all the circumltanees which are ca- 

 pable of modifying the powers brought into action, at the 

 moment of their fucceflive precipitation, and which will deferve 

 a particular examination in another memoir. But when the 

 metals are mutually precipitated from their folutions, their 

 reciprocal affinity for oxygen has a great effect in the action 

 that takes place; and fometimes the precipitate is found in 

 the metallic ftate. If another force were not joined to the 

 affinity of the precipitating metal for oxygen, it would natu- 

 rally follow, from the principles eftablifned in this memoir, 

 that the oxygen would divide itfelf between the two metals 

 which are in competition, according to the action they exert 

 itponjt. It is therefore necelfary to examine what may be 

 the force which determines the precipitation in the metallic, 

 ftate. 



2. The affinity of mercury, gold, and filver, for oxygen, is 

 very weak : the mutual affinity which itill remains between 

 the parts of thefe metals when they are in fuiion, as mercury 

 is at the temperature of the atmofphcre, is fufficient to pre- 

 vent their combination with oxygen in the ftate of gas; but 

 heat, by dilating the particles of the mercury, diminiflies the 

 force of their mutual affinity fufficiently to enable them to 

 combine with oxvgen ; while a fuperior degree of heat, by 

 the difference of dilatation which it produces in the mercury 

 and in the oxygen, will feparate them : heat, then, contri- 

 butes to this combination bv diminithing the mutual affinity 

 of the parts, but at length, by augmenting this difference, it 

 renders their combination impoflible. As the force of co- 

 helion in mercury is fufficient to prevent oxidation, this very 

 force will tend to effect its deoxygenation, with the afliftance 

 of a metal which will act directly upon the oxygen. It is a 

 force analogous to that which produces cryftallization and 

 precipitations. (Art. V.) 



3. The particles of a metal have not only a mutual affi- 

 nity, but likeWife an affinity for thofe of other metals : hence 

 proceed the amalgams and mixtures. It is only necefTary to 

 put copper in contact with mercury to effect a combination 

 between thefe two metals. Thus, when a metal oppofes its 

 aciion to a metallic folution, part of the metal may act upon 

 the oxygen and upon the acid, while the other tends to com- 

 bine with the metal of the oxide. Let us fee whether we can 



difcover, 



