P O I 
Red oxyde may be difl'olved in muriatic acid, and is 
thereby changed into corrofive fublimate. The cinnabar, 
or vermilion, is infoluble in water and muriatic acid. 
The mercurial ointment boiled in water is decompofed ; 
the lard is melted, and the mercury depofited. 
Arfenical Preparations .—White arfenic (deutoxyde of 
arfenic) is of a white colour, like fugar, but differs con- 
iiderabiy therefrom, being much heavier. It is volati- 
lized, and diffufes a fmell like garlic when placed on hot 
copper. It is not difl’olved by cold water; and laltly, it 
becomes of a very fine green when put into a folution of 
the blue ammomacal fulphate of copper. Arfenical acidis 
white, and alfo gives out a fmell of garlic when placed on 
hot iron or burning coals ; it is eafily difl'olved in water, 
and changes its colour to a fine blue when mixed with 
the ammoniacal fulphate of copper. Orpiment is yellow; 
heated to rednefs with potafh, it diffufes the vapours of 
arfenic, which fmell like garlic. Realgar is red, and 
does the fame as orpiment when mixed with potafh and 
heated. There is a powder fold to deftroy vermin : this 
is the black oxyde of arfenic; it gives ofF an odour of 
garlic when heated, and becomes green when left for 
tome hours in a folution of the blue ammoniacal fulphate 
of copper. 
Many delicate and curious tefts have been invented to 
detedt arfenic; but the following is preferable to them all. 
It is felefted from an excellent paper, by Dr. Chriftifon, 
in the Edinburgh Medical Journal. The author, having- 
clearly pointed out the inutility of the modes adopted by 
Orfila, Peris, Philip, 2nd others, informs us that the fol¬ 
lowing procefs will detedt arfenic when mixed with vege¬ 
table or animal folids or fluids, or with any mineral 
“ with which it cannot form under the adtion of boiling 
water an infoluble compound.” If the fufpedted matter 
be a folid, let it be boiled brifkly in two or three fuccef- 
flve portions of pure water; if in a fluid ftate, it will only 
be necefl'ary to boil and filter the fluid, and to add a fmall 
portion of acetic acid, by which agent the influence of any 
extraneous alkali will be counteracted, and other fub- 
ltances coagulated and feparated. The fluid is now to 
be placed in a deep narrow glafs, and the tefi applied. 
This is a brifk ftream of fulphuretted hydrogen gas, which 
having been continued for half or three-quarters of an 
hour, a precipitate is formed at once yellowifh; or a 
milkinefs is obferved in the fluid, which pafles to a dif- 
tindt precipitate as foon as the excefs of fulphuretted 
hydrogen is given off by heat. Before we attempt to 
feparate the precipitate, the fluid fliould be again boiled. 
After this, when the mixture is perfedlly fettled, we fliould 
decant off the fuperabundant liquor, and filter the preci¬ 
pitate, and dry it at a temperature iomewhat above 212 0 . 
It is now to be reduced. The precipitate being placed 
in a glafs tube (clofed at one end, three inches in length 
and from one-eighth to one-quarter of an inch in diame¬ 
ter), heat is to be gradually applied by means of a f'pirit- 
lamp. We now obferve that a watery vapour is evapo¬ 
rated, and condenfed on the fuperior part of the tube; 
this mull be removed with a bit of filtering-paper. Next, 
from the decompolition of the animal or vegetable mat¬ 
ters, charcoal in the form of black vapour condenfes on 
the tube : lallly, the arfenic fublimes, when tlie difcharge 
of carbonaceous vapour has nearly ceafed, “and it always 
condenfe's lower down and within the fliortell poflible 
diftance from that part of the tube which is expofed to 
the flame.” The true arfenical cruft is known by the 
following characters. Its outer ftirface, or that next the 
tube, exactly refembles highly-polifhed flee! ; its inner 
lurface is juft like a fraCtureof fine iteei if the quantity 
be confiderable; but, when very minute, it has a dull 
biue-grey hue: a magnifier, however, of four or five 
power, (hows the brilliant and cryltaliine appearance. 
Befides thefe appearances, the following aualyfis affords 
•evidence of the arfenical cruft. “ The part of the tube to 
which the arfenic adheres, being broken, is to be left for 
tome hours in a watch-glafs containing a dilute folution 
Vol, XX. No. 14.12. 
SON. 821 
of the ammoniacal fulphate of copper. In four or five 
hours the metallic cruft will become grafs-green, or, if very 
minute, will be difl’olved; but then a brilliant grafs-green 
cruft is formed on its furface. It is to be noted, that the 
ammoniacal folution juft mentioned will, when boiled, 
have a cruft on its furface, though no arfenic has been 
added, but then the colour is azure blue. We obferve 
the hue beft by flcimming the furface with a bit of ltifF 
white or blue paper.” This mode will deteCt arfenic 
eafily, when difl'olved in 8000 times its weight of liquid. 
Preparations of Copper, difl'olved in water, are for the 
moll part of a blue or green colour. The Prufliate of potafh 
caufes a reddifh brown precipitate. Metallic iron\and 
phofphorus decompofe them immediately, and the copper 
in a metallic form is precipitated. Artificial verdigris 
does not altogether diftolve in cold water; boiled in wa¬ 
ter, it gives a blue liquor and a deep-brown powder. 
Heated to rednefs in a crucible, it is decompofed, and 
metallic copper is found at the bottom. 
The molt delicate tell of the pretence of copper in any 
fluid, is a folution of pure ammonia, which imparts to it 
a beautiful blue colour. If the folution fufpedted to con¬ 
tain copper be very dilute, it fliould be concentrated by 
evaporation; and, if the liquor contain a confiderable 
excefs of acid, like that ufed to preferve pickles, as much 
of the alkali inuft be added as is more than fufficient to 
faturate the acid. 
Preparations of Antimony. —By heating all thefe pre¬ 
parations to rednefs in a crucible, we obtain a metallic 
button, eafily to be known ; firlt, by its whitifh-blue 
colour; f'econdly, by the property it has, when heated 
with nitric acid, of giving a white powder lbluble in 
muriatic acid. Sulphurous acid, added to this folution, 
throws down an orange-coloured precipitate, and water 
a white precipitate. Tartar emetic is white: placed 
upon burning coals, it becomes black, and leaves metallic 
antimony; it is foluble in water, and the folution is not 
changed by diftilled water; fulphuric acid occafions an 
orange precipitate, and gall-nuts a vvhitiflt-grey. 
Kermes is of a deep brownifh-red colour, but changes 
to whitifh-yellow when heated with potafh diffolved in 
water. The golden fulphuret does the fame when heated 
with potafh; but then it is naturally of an orange- 
colour. 
Butter of antimony is a dark fluid; mixed with water, 
it gives rife to a white precipitate. The other falts in 
folution are precipitated white by water, orange or red 
by fulphuric acid and the hydro-fulpliates. The oxydes 
are foluble in muriatic acid, and the fait thereby formed 
is known in the manner we have juft fpoken of. 
The Salts of Tin arc not precipitated by diftilled water; 
but potafh caufes a white, and the hydro-fulphaces a yel¬ 
low or chocolate, precipitate. The Salts of Bifmuth are 
precipitated of a white colour by diftilled water, and of a 
black by the hydro-fulphates. Salts of Gold are yellow, 
and are precipitated of a black colour by green vitriol. 
Salts of Zinc of a white, by potafh and the hydro-ful¬ 
phates. 
Nitrate of Silver, heated to rednefs, the metal is reduced. 
Diflolveil in water, and mixed with a folution of muriate 
of foda, a white precipitate is thrown down. Pholphate 
of foda occafions a yellow, and chromate of potafh a red, 
precipitate. The precipitate by chromate of potafh is 
reddifh brown when the liquids are mixed hot ; purpliih- 
red, when they are mixed cold; and carmine red when 
the .chromate of potafh contains an excefs of acid. It 
becomes brown when expofed to the light, and is foluble 
in nitric acid. 
Nitre. —It is highly necefl'ary to diftinguifli nitre from 
Glauber’s fait, with which it has been confounded. 
Placed upon burning coals, nitre crackles and gives-afine 
white flame ; on the contrary, Glauber’s fait melts, fwelis, 
and becomes opake. Mixed with fulphuric acid, it throws 
oft' white vapours; nothing fimilar to this is obferved in 
the cafe of Glauber’s fair. 
9 Z Sal 
