On the Purification of Mercury. 349 
purifying mercury in the state here described. Nevertheless 
Messrs.Guyton*, ‘Brugnatelli +, Virey t, and other chemists, have 
justly observed, that in this operation a small part of the fixed 
metals rises with the mercury in the state of vapour; and MM. 
Klaproth and Wolff§ assert, that it is extremely difficult by this 
means to separate all the bismuth. The iron filings which, ac- 
eording to Nollet, ought to be put into the retort over the mer- 
cury to be refined, in order that when the metal rises in vapour 
it must pass between the particles of iron, assuredly do not con- 
tribute to produce a better result ; and in fact, no modern au- 
thor whose works I have been able to consult, recommends the 
above addition to the process. The continued agitation of this 
mercury in contact with the air was announced by Priestley as 
capable of purifying it. If (said he) it is a long time agitated in 
a stopped decanter of whose capacity it does not occupy above 
a fourth part, and the air in the decanter be repeatedly renewed 
by means of bellows, the foreign metal will be converted into 
oxide, and the mercury become so pure as to resist all proof of 
extraneous matter by distillation. Nicholson, who said that he 
had repeated this method with success, recommended it to ma- 
thematical-instrument-makers, who had not the necessary ap- 
paratus for distillation. But Guyton with some very just observa- 
tions dissents from this, and is of opinion that the adulterated 
mercury cannot by such means be liberated from all extraneous 
matter ||. 
In the year 1798, considering that at the temperature of the 
atmosphere, some acids, as for example the sulphuric, do not 
dissolve mercury, although they unite with more or less facility 
to the above-mentioned metals, it occurred to me that it might 
be practicable to purify adulterated mercury by immersing it in 
one of these acids and repeatedly changing its surface. The 
result obtained by this kind of parting having answered my ex- 
pectations, I have always used the same method on sueceeding 
occasions, and it is well known to many persons, who at my sug- 
gestion have put it in practice. Nevertheless I do not pretend 
that by such a process this mercury becomes perfectly pure, but 
only in a state fit for use in a great number of experiments. The 
most pure is justly considered by chemists as solely that which is 
separated from cinnabar by the united action of caloric and 
iron filings, or that which by the effect of caloric alone is ob- 
tained from what is called red precipitate—that ig, the red oxide 
of mercury, by means of nitric acid J. 
* Annales de Chimie, xxv. 79. + Trattato Elementaive di Chimica 
Generale, iii. 136. t Traité de Pharmacie, ii. 356. § Dizionario 
di Chimica del Sig. Prof. Morerni, iii. 93, 101. || Annales de Chimie, 
KXv, 77. 9) Thus silver of cupellation i is pure ; but the purest is that 
which is obtained by the decomposition of muriate of silver. 
Neither 
