the TD [[folution t>f Metals in Acids* 
the affinity of iron to acids in general is known to be much 
ftronger than that of filver ; and although, even with regard 
to the nitrous acid, other experiments evince the fuperior 
affinity of iron : for as iron precipitates copper from this acid, 
and as copper precipitates filver, we muft infer the greater 
affinity of iron than of filver. In the courfe of his experi- 
ments, however, fome infiances of precipitation occurred, 
which he attributed to the peculiar quality of the irons which 
he then employed I was defirous of difcovering the circum- 
ftances, 
* Bergman tried many different kinds of iron, and he thought he found two 
which were capable of precipitating filver. But as he did not difcover the cir~ 
cumftances according to which this precipitation fometimes does, and at other times 
does not happen, he may have been miftaken with regard to the peculiar quality 
of thefe two kinds of iron. At leaft the feveral kinds which I have tried always 
precipitated filver in certain circumflances, and always failed to precipitate in 
certain other circumflances. I do not know any other author who has men- 
tioned this fubjeCt, excepting Mr. Kirwan ; who, in the conclufion of his 
valuable Papers on the AttraElive Powers of Mineral Acids , fays, 44 I have always 
64 found filver to beeafily precipitated from its folution in the nitrous acid by iron. 
4 4 The fum of the quiefeent affinities being 62$, and that of the divellent 746'° 
44 Yet Mr. Bergman obferved, that a very faturated folution of filver was very 
44 difficultly precipitated, and only by fome forts of iron, even though the folution 
44 was diluted, and an excefs of acid added to it. The reafon of this curious 
44 phenomenon appears to me deducible from a eircumflance firft obferved by 
44 Scheele, in diffolving mercury, namely, that the nitrous acid when faturated 
44 with it will take up more of it in its metallic form. The fame thing happens 
44 in dilfolving filver in the nitrous acid in a ilrong heat ; for, as I before 
44 remarked, the laft portions of filver thrown in afford no air, and confequently 
44 are not dephlogifticated. Now this compound of calx of iilver, and filver in 
44 its metallic form, may well be unprecipitable by iron, the filver in its metallic 
44 form preventing the calx from coming into contact with the iron, and extracting 
44 phlogifton from it.” In this Paper I fliall not enter into the explanation of 
thefe appearances ; but I thought it neceffary to premife what fo eminent a che- 
mifi: as Mr. Kirwan has fuggeffed on the fubjeCt, that the reader may fee at once 
the prefent ftate of the queftion. I fliall only remark, that the above explana- 
