g8 Ttiquiry into the Laws of Affinity, 



cury, as I fuppofed, (Memoirs of the Academy, 1780) but becaufe the expanfive force of the 

 beatj and the tendency to the combination of the muriatic acid, a£b»ng upon the oxide of 

 mercury, caufe, as we may exprefs ourfelves, a new (haring to be made of it. If the pre- 

 cipitate by ammonia be examined, it is obferved, that it retains a portion of ammonia : the 

 precipitate of the muriate of iron by pot-afli, retains part of the pot-afli. Fa£\s of this 

 kind may be colie£ted in great number. 



There is therefore no doubt, but that the obfervations which have been made upon the 

 precipitations of fubftances which lofe their folubility, cannot be applied to the metallic 

 precipitates, which vary according to all the circumftances which are capable of modifying 

 the powers brought in action, at the moment of their fucceflive precipitation, and wliich 

 will defervc a particular examination in another memoir. 



But when the metals are mutually precipitated from their folutions, their reciprocal affi- 

 nity for oxigen has a great effedt in the aftion that takes place ; and fometimes the precipi- 

 tate is found in the metallic ftate. If another force were not joined to the affinity of the 

 precipitating metal for oxigen, it would naturally follow from the principles eftabliflied in 

 this Memoir, that the oxigen would always be divided between the two metals which are 

 in competition, according to the a£tion they exert upon it. It is therefore neceflary to 

 examine, what may be the force which determines the precipitation in the metallic ftate ? 



2. The affinity of mercury, gold, and filver for oxigen is very weak: the mutual affinity 

 which ftill remains between the parts of thefe metals when they are in fufion, as mercury 

 is at the temperature of the atmofphere, is fufficient to prevent their combination with 

 oxigen In the ftate of gas ; but heat, by dilating the particles of the mercury, fufficiently 

 diminiflies the force of their mutual affinity to enable them to combine with oxigen: a fu- 

 perior degree of heat is fufficient, by the difi"erence of dilatation which it produces in the 

 jnercury and in the oxigen, to feparate them ; fo that the a£tion of the heat begins by 

 being more effe£live to this combination, in confequence of the diminution of the mutual 

 affinity of the parts, than inimical to it by the different dilatation of the mercury and the 

 oxigen : but at length by augmenting this difference, it renders their combination im- 

 poffible. 



As the force of cohefion in mercury is fufficient to prevent oxidation, this very force will- 

 tend to efieft its difoxigenation, with the affiftance of a metal which will aft dire6tly upon 

 the oxigen. It is a force analogous to that which produces cryftallifation and precipita- 

 tions. (Art. V.) 



3. The metallic particles have not only a mutual affinity, but likewife have an affinity 

 IFor thofe of other metals: hence proceed the amalgams and mixtures.. It is only neceffary 

 to put copper in contaft with mercury to effedl a combination between thefe two metals. 

 Thus when a metal oppofes its action to a metallic folution, part of the metal may aft upon 

 the oxigen and upon the acid, while the other tends to combine with the metal of the 

 oxide. Let us examine, whether we can difcover in the precipitation of mercury, filver 



gold 



