Experiments' and Obfervations , 9 
about an hour after were not in the lea if attracted by it. The 
method which, when the furface of the quickfilver is rendered 
thus fluggifh, will effectually purify it, is to pafs the quick- 
filver through a funnel of paper, viz. a piece of clean writing 
paper rolled up conically, and having at its apex an aperture of 
about a fiftieth part of an inch in diameter; which operation is 
fometimes neceflary even on firft pouring out the quickfilver, 
and which 1 have often been obliged to repeat three or four 
times in the courfe of an hour. There feems to be formed a 
kind of cruft upon the furface of the mercury when expoled, 
which, though invifible by mere infpeCtion, may be perceived 
by moving the floating body ; for if it be tried immediately after 
having patted the quickfilver through the paper funnel, the 
floating fubftance will feem to proceed byitfelf; whereas, fome 
time after, the fame body, when moved, feems to communi- 
cate that motion to the adjacent quickfilver, and to drag it 
along with itfelf, fomewhat like when one moves a body, 
which floats upon the furface of a liquor that begins to 
coagulate. 
The formation of this cruft feems to be moftly owing to the 
imperfeCt metals, which in various quantities are ufually amal- 
gamated with the common fort of quickfilver ; becaufe that 
amalgamation tends todephlogifticate thofe metals, and the fe mi- 
calcined part floats at the top, and it is not unlikely that the 
dephlogiftication goes on much quicker in the open air. The 
reality of this fuppofition is corroborated by obferving, that 
the purer the quickfilver is, the fmaller is the cruft formed, or 
oppofition made to the floating bodies. However, I have 
obferved it in fome meafure even in the pureft quickfilver that 
can be procured ; and am inclined to think, that it thufl be 
Vol. LXXVII. C partly 
