REMARKS ON SOME OP THE MERCURIAL COMPOUNDS. 47 
Brande, Gay Lussac, and a number of others asserting that it 
is unaltered, when pure, by exposure to air. Lagrange, Mur- 
ray, Nicholson, Priestly, Fourcroy and others, on the con- 
trary, that it slowly assumes the state of a protoxide. 
Wood and Bache, in the U. S. Dispensatory, assert that 
"when perfectly pure, it undergoes no alteration by the ac- 
tion of air or water, but in its ordinary state suffers a slight 
tarnish," and follow it up by saying that " mercury, as it oc- 
curs in commerce, is very pure" From repeated observa- 
tions, however, it is satisfactory to me, that pure as the metal 
may be, when exposed to air repeatedly, a gray film forms 
on its surface, which is increased by agitation and other cir- 
cumstances to be alluded to hereafter; the mercury used in 
these observations has not only been carefully distilled, but 
also tested by appropriate chemical agents to prove its entire 
separation from any other metals with which it is sometimes 
adulterated, and which impart to it a facility of oxidation. 
By continued agitation it has been long known that this 
change is easily accomplished, as even in the time of Bcer- 
haave, (who first obtained it by subjecting mercury to the 
motion of windmills, carriage wheels, &c.) this fact was well 
known, and the oxide designated Ethiops per se, and many 
of the authors who have denied its capability of oxidation by 
exposure to air, grant, that combined with agitation, this 
change is easily accomplished; there seems to be no doubt in 
this respect, that mercury when exposed to the action of air, 
becomes slowly oxidized and more rapidly when agitated; 
" by long agitation with access of air it becomes converted 
into a black powder or oxide, which gives out oxygen by heat, 
the metal being at the same time revived. "* 
The presence of extraneous matter is, however, acknow- 
ledged by all to facilitate this change. " It is oxidated even 
at natural temperatures when subjected to agitation, or still 
more easily, when triturated with any viscid matter, which 
is interposed between its globules so as to extend their sur- 
face;"! Dut ^ does not require the aid of trituration to effect 
*Ure. 
t Murray Mat. Med., 1827. 
