Encyclopaedia Britannica, or, a Dictionary of arts, sciences, and miscellaneous literature : enlarged and improved. Illustrated with nearly six hundred engravings > Volume 18, RHI-SCR

AMUSEMENTS 'OF SCIENCE. 553
hemical for a-defcrlption am! explanation of them, to the above
Ihecrea- article, and to the principal elementary works on mo-
t'0“s’ dern chemiftry, efpecially the Epitome qf Chemiflry% by
1 ' Dr William Henry (8vo edition), to which the follow¬
ing enumeration will chiefly refer.
Among the more curious and interefling experiments
of chemiftry, We may notice the combuftion produced
by wrapping nitrate of copper, {lightly moiftened, in a
fheet of tin foil (Henry, p. 15.) ; the reflection of heat
and cold from the furface of concave mirrors (CfiEMiS-
‘TRY, N° 170, or Henry, p. 28.); the artificial produc¬
tion of great degrees of cold, fo as to freeze mercurij
and alcohol (CHEMISTRY, 274, or Hehry, p. 36.) 5 the
experiments of Dr Herfchel, thewittg that the fun emits
rays which heat without illuminating ; others which il¬
luminate without heating) and others which neither illu¬
minate nor heat, but produce evident chemical changes
(Chemistry, 172, or Henry, p. 48.) ; the combufion
<f charcoal, phofphorus, and iron wires, in oxygenous gas,
and more efpecially the combuftion of metals in a com¬
bined ftream of oxygen and hydrogen gafes (Henry,
p. 60.) ; the explofon of hydrogenous and oxygenous
gafes, and confequent produ6tion of water (Chemistry,
382, and Henry, p. 70.) ; the decompoftion of ivater
(Chemistry, 384, or Henry, p. 78.) the effeft of al¬
kalies and acids in changing the colour of blue vegetable
infufions to green and red (Henry, p. 102.) ; the com¬
buftion produced by mixing nitric acid with ejfential
oils, or other combuftibles (Chemistry, 510, and
Henry, p. 151.) > the combuftion produced by throw¬
ing metallic particles into oxygenized muriatic acid gas
(Henry, p. 181.) j the deflagration of hyperoxygenized
muriate of potafh, with phofphorus and other combuf¬
tibles (Chemistry, 962, et feq. or Henry, p. 187.);
the production of phofphorated hydrogen gas, by throw¬
ing phofphurel of lime into water, (Henry, p. 197.) ;
and the decompofition of metallic folutions, fo as td pro¬
cure the metals in a pure or metallic ftate.
As thefe laft experiments are only incidentally no¬
ticed in the article Chemistry, and in Dr Henry’s
Epitome, we fhall here deferibe tv/o of the moft curious
j3 inftances of what have been called metallic vegetations,
t >or Di- The firft of thefe which we fhall notice is called Ar-
bor Diance, the tree of Diana, or the filver tree, as it is
produced by deeompofing a folution of fiver, fo that the
filver is exhibited in the metallic ftate, and in an arbo-
refeent form. There are two methods of producing the
arbor Diance,or\t by Homberg, and the other by Beaurre.
According to Homberg’s method, an amalgam is to
be formed by rubbing a quarter of an ounce of very
pure mercury, and half an ounce of fine filver reduced
to leaves or filings, by triturating them together in a
porphyry mortar, with an iron peftle. This amalgam
is to be diflblved in four ounces of the pureft nitric acid
of a moderate ftrength, and the folution is to be diluted
with about 24 ounces of diftilled water. An ounce of
this liquor is to be poured into a glafs, and a fnaall piece
of a fimilar amalgam of mercury and filver, of the oon-
fiftence of butter, is to-be introduced. Soon after there
may be fee rifing from the ball of amalgam a multitude
of fmall fhining filaments, which vifibly increafe in
number and fize, and throw out branches, fo as to form
a kind of fhrub.
Beaume’s method is as follows.—Six parts of a folu¬
tion of filver in nitric acid, and four of a folution of
Vol. XVIII. Part II.
mercury in the fame acid, both in a ftate of faturation, Chemical
are to be mixed together, and a fmall quantity of di-
{tilled water to be added. This mixture is to be poured - J
into a conical glafs veflel, containing fix parts of an am¬
algam made of {even parts of mercury and one of filver.
At the end of fome hours there will appear on the fur-
face of the amalgam a metallic precipitate in the form
of a vegetation.
The other experiment which we have to deferibe is Tree of
that of producing a leaden tree, which, as it may be lead,
performed on a large fcale, and at a trifling expence, is
preferable-to the former. The method of effecting this
decompofition which we have found moft effectual, is
the following.
Diffolve in diftilled or pure rain water a quantity of
acetate of lead (fugar of lead), not fufticient to faturate
it 5 viz. in the proportion of four fcruples of the fait to
the Englifh pint of water. When the folution has be¬
come clear, pour it into a cylindrical vefl’el, or a glafs
wine decanter of confiderable fize, and introduce into it
an irregular piece of pure bright zinc, fufpended by s.
firing, or a piece of brafs wire. In the courfe of a few
hours, the zinc will be covered with a dulky grayifli
mafs, having the appearance of mofs, and from this are
gradually fhot out plates or leaves of a brilliant metallic
fubftan’Ce. Thefe will extend themfelves towards the
bottom of the veffel, and will form trunks, branches, and
leaves, fo as to refemble a leaden tree fufpended by its
roots from a mofly hill. In this way we have produced
a vegetation that has nearly filled a cylindrical glafs-jar
of a foot in height, and four or five inches in diameter.
Sect. V. Recreations and Contrivances relating to
Electmcitt.
The fubjeft of ele&ricity, like that of chemiftry, af-Eletftrici!
fords ample room for fcientific recreations. Of thefe recreations
we have given a large colleftion in bur treatife on
Electricity, and fhall here only enumerate the more
ftriking experiments.
Thefe are, the phenomena produced by paper when
excited by caoutchouc or Indian rubber (fee Electri¬
city, Part I. Chap. 3.) j the experiments of the dan-
cing-fgures, dancing-balls, illuftrating eleiftrical attrac¬
tion and repulfion j the eleBrical orrery, and eleBrifed
cotton, illuftrating the aftion of points; the eleBrifed
fpider ; the magic piBure, 'eleBrical jack, fe If moving
wheel, fpiral tube, luminous conduB.r, aurora borealis,
eleBrifed can and chain, and the thunder-houfe.
Sect. VI. Amufements and Contrivances relating to
Galvanism.
The fubjeift of galvanifm, though fo nearly allied toGalv**jc
electricity, is capable of fupplying ftill more exfraordi-ann fe¬
nary experiments, many of which are often witnelfed ments.
with furprife and admiration. Many of thefe have been
related in our treatife of Galvanifm. The moft firiking
of thefe are, the mufcular contractions produced in dead
animals, efpecially thofe of Aldini (Galvanism, N°
35.) i the combuftion of charcoal (N° 42.) j the de¬
flagration of metals (N° 43.) ; and the decompofition
of water (N° 44.). The experiments ou deflagrating
the metals, and on other perfect conductors, fucceed beft
with a trough of very large plates of zinc and copper %
but experiments on animal bodies, and other imperieil
4 A conductors,