S T R Yi 
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lent vermifuge. It is by virtue of this property likewife 
that it cures the itch, and other cutaneous diforders. 
Rubbed for a fhort time between the fingers, it emits a 
flight peculiar fmell. When it is very pure, and is agi¬ 
tated, it is fometimes obferved, more efpecially in hot 
weather, to fhine with a fmall phofphoric light clearly 
difcernible. This phenomenon has been fhewn with the 
mercury of the barometer by feveral natural philofophers. 
If the hand be plunged in this metallic fluid, a fenfation 
of cold is perceived, -which feems to (hew that its tem¬ 
perature is much beneath that of the atmofpheric air; 
yet, by plunging a thermometer in the fame mercury, it 
is immediately 1'een that their temperatures do not differ. 
This efteCl, which deceives us, is to be attributed en¬ 
tirely to the great rapidity with which the heat pafles 
from the hand into the mercury, for this metal is known 
to be a powerful conduftor of heat. 
Mercury, when divided by continual agitation, fuch 
as that of the fails of a mill, changes by degrees into a 
very fine black powder, called Ethiops per fe, by reafon of 
its colour. As the mercury experiences a commence¬ 
ment of combuffion in this experiment, this powder is 
called black oxyd of mercury. The mercury, by a flight 
heat, or by trituration in a warm mortar, may be made 
to refume its ufual fluidity and brilliancy; and, if the 
experiment be made in dole veflels, with the pneumatic 
apparatus, oxygen gas will be obtained : if, after being 
. fprinkled with ammoniac, it be expofed to the fun’s rays, 
it changes into metallic globules. 
We have before remarked, that mercury is eafily re¬ 
duced into vapours by the aflion of fire; hence diftilla- 
tion is the bell method of purifying it, and of feparating 
the matters with which it is ufually vitiated in com¬ 
merce. For this purpofe, put the mercury into a glafs re¬ 
tort, and fufpend to its neck a bit of flax, which is juft: 
to dip into the water contained in the matrafs or balloon 
adapted to the retort; then proceed to diffillation. If 
the mercury is pure, it pafles over entire, without altera¬ 
tion or diminution; if it contained any foreign or ex¬ 
traneous matters, they will remain at the bottom of the 
retort; often there will be left a fmall quantity of a grey 
powder, which is only a little of the mercury oxydated 
by means of the air contained in the veflels. Boerhaave 
diftilled the fame quantity of mercury five hundred times 
fucceffively, and found it not in any refpeft altered. It 
only appeared more brilliant, heavy, and fluid; doubt- 
lefs becaufe the purification was very accurate. In 
this diftillation he obtained a fmall quantity of the grey 
powder juft fpoken of. It was black oxyd of mercury 
produced by the air contained in the apparatus. 
Mercury, reduced into vapour, has a very confiderable 
force of expanfion, and is capable of producing danger¬ 
ous explofions when confined. Hellot related to the 
French Academy, that a certain perlon, being defirous 
of fixing mercury, had put a quantity into an iron-ball, 
well foldered together. The ball being thrown into the 
middle of a heated furnace, had fcarcely become red, 
when the mercury burft through its confinement with a 
great report, and efcaped. Beaume, in his Experimental 
Chemiftry, relates a fimilar fa£l. 
Mercury is infinitely more fufceptible of oxydation by 
the contaft of air, and many other bodies, than has hi¬ 
therto been fuppoled, A grey blackifh pellicle is con¬ 
tinually formed upon its furface, which is a true oxyd 
of mercury. Heated with the concourfe of air, this me¬ 
tal, at the end of fome days, becomes changed, into a 
brilliant red powder, of an earthy appearance, difpofed 
in fmall fcales. This powder, which no longer pofiefles 
the metallic afpeCl, is a true mercurial oxyd. The al- 
chemifts, who believed that the mercury was fixed in 
this experiment, called it, improperly, mercury precipi¬ 
tated by itfelf, or precipitate per fe. As mercury, though 
very volatile, requires neverthelefs the concourfe of air 
to calcine it, an inftrument fufficiently commodious has 
been invented for this operation, ufually .called Boyle's 
Vol. IV. No. 196. 
281 
Hell. It is a large glafs veflei, flat at the bottom, fo 
that the mercury, enclofed within it, forms a very thin 
ftratum, and confequently prefents a large furface. It is 
clofed by a large Hopper, accurately fitted to its neck, 
and perforated by an exceedingly fmall hole. The vefitl 
is placed on a fand-bath, and the mercury heated till it 
boils. The opening in frhe Hopper, on account of its mi- 
nutenefs, allows the air to have accefs to the bottle, with¬ 
out fullering. the mercury to efcape. At the end of feve¬ 
ral months of digeltion, an oxyd, which is formed on 
the furface of the mercury, may be feparated. This is 
done by pouring the whole into a piece of clofe linen; 
the mercury pafles through by preflure, and the red oxyd 
remains on the cloth. This procefs may be performed 
with equal fuccefs, with a flat-bottomed matrafs, into 
which a fuflicient quantity of mercury is poured to form 
a thin ftratum. The neck of the matrafs is afterwards 
drawn out into a-capillary tube, and the point broken 
oft'. This method, contrived by Beaume, is better adapt¬ 
ed to the oxydation of mercury, becaufe the veflei con¬ 
tains more air. It is likewife more eafily heated, lefs ex- 
penfive, and lefs fubjeCl to be broken, than Boyle’s vef- 
fel. To fucceed in this experiment, the mercury mull: 
be kept in a heat fuflicient to make it boil gently night 
and day for feveral weeks. By placing a number of fuch 
veflels on the fame fand-bath, a very large quantity of 
precipitate per fe, or red oxyd of mercury, may be ob¬ 
tained, and a certain quantity may be had in fifteen or 
twenty days. It has been propofed to abridge this labour 
by ufing a glafs veflei, which has a neck about half an 
inch in width and four feet long, and of which the bot¬ 
tom part is not more than three or four inches in dia¬ 
meter. Half a pound of mercury having been intro¬ 
duced into this veflei, and its mouth covered loofely with 
a bit of paper, fo as not to exclude the external air, it is 
to be placed in a fand-bath, and an uninterrupted heat 
applied to it, fuflicient to raife the vapours of the mer¬ 
cury about two feet in the veflei. This procefs will be 
facilitated by removing, from time to time, the oxyd 
which is formed, and which covers the fluid mercury. 
The precipitate per fe is a true oxyd of mercury, or 
combination of metallic fubftance, with oxygen, which 
it gradually feizes from the atmofphere. This is proved 
in a convincing manner, from the following circum- 
ftances : 1. Mercury can never be converted into preci¬ 
pitate per fe, without contact of air. 2. This combina¬ 
tion cannot be made but with vital air, and does not 
take place in the different gafes which are not pure air. 
3. The mercury in this experiment becomes heavier. 4. 
When heated in clofed veflels, it may be entirely reduced 
into running mercury, at the fame time that a large 
quantity of elaftic fluid is difengaged, in which combuf- 
tible bodies burn four times more rapidly in the air of 
the atmofphere. This is the fame fluid that was firft 
difcovered by Dr. Prieftley, and by him called depblogif- 
ticated air, and which we now call oxygen gas, or vital 
air. Before it is entirely reduced, it returns to the 
orange and the yellow colour; and, if the operation be 
flopped at the moment it is on the point of being re¬ 
duced, it will be found in a black powder. 
The red oxyd of mercury may be turned black alfo by 
contadl with pure ammoniac ; in which operation azotic 
gas is difengaged, proceeding from the decompolition of 
the ammoniac. This oxyd may alfo be reduced by light. 
If this red oxyd of mercury be triturated with running 
mercury, a black oxyd of mercury is produced; the ex¬ 
tinction is very quick, and may be ufed with advantage, 
whenever it is defirable to bring mercury to this Hate to 
combine it with fat fubftances, or indeed any other. 
Mercury combines very readily with fulphur. When 
one part of this metallic fluid is triturated with three 
parts of fulphur, the mercury is gradually extinguifhed, 
and a black powder is produced, being the black ful- 
phure of mercury, formerly called JEtbiops mineral, ’and 
whofe colour becomes deeper fome time after it is made. 
4 C This 
