852 
C H E 
CHE 
CHE 
the rays of light will suffer no interruption 
in passing through them, if however, to 
this solution of silver, a quantity of mer- 
cury is added, the aqua-fortis will be at- 
tracted by the mercury, and the silver will 
be thrown down or precipitated to the 
bottom ot the vessel in which the fluid is 
contained. (Hence the chemical term 
precipitation.) If again copper is added, 
it will assume the place of the mercury, 
which of course in its turn will be preci- 
pitated. If to this solution of copper, a 
piece of bright iron (for rust would prevent 
the action of the acid) is introduced, the 
surface of the iron will be dissolved, and 
the copper precipitated, and will be de- 
posited on the bar of iron. The iron may 
afterwards be precipitated by the intro- 
duction oi an alkali. On this principle 
are founded the tables of affinity or elec- 
tive attraction, which state the substances 
in order as they have an attraction for each 
other. It is a general maxim in chemis- 
try, that for bodies to act in this manner 
on each other, one of them must be in a 
fluid state. A double elective attraction 
or affinity is, when two bodies, each com- 
pounded of two principles, mutually 
change a principle of each. Thus, when 
the salt which is compounded of mercury 
with nitric acid is presented to a solution 
ot vitriolated tartar, the vitriolic acid will 
quit the alkali, and unite with the mercury, 
mid the nitric acid will combine with the 
alkali. This is also sometimes called the 
attraction of combination. 
■Calcination, applied to the metals, is their 
oxygenation by means of heat. 
Concentration, the separation and evapora- 
tion by means of heat of the watery par- 
ticles from any fluid; by which the fluid 
is said in common language to become 
stronger, or less diluted. 
Crucible, a vessel usually made of clay, em- 
ployed as a melting-pot for metals or other 
substances. 
Crystallization, is when a body passing from 
a fluid to a solid state, assumes a regular 
form. See the article Crystalliza- 
tion. 
Decantation, the separation of a fluid from 
the solid concrete particles which it con- 
tains. This is done by leaving the fluid 
at rest in a conical vessel, when the foreign 
matter will deposit itself at the bottom, 
and if the fluid is very gently poured off it 
will be obtained tolerably clear. A sy- 
phon is sometimes employed with advan- 
tage when the matter deposited is light, 
and there is danger of shaking the vessel. 
A thick woollen thread steeped in the 
liquor, and inclining over the edge of the 
vessel into another, makes a very good sy- 
phon for this purpose. 
Decoction is the extracting, by the applica- 
tion of heat and moisture, of some por- 
tion of matter from certain substances, as 
the gums and essential oils from vegetables. 
When the extract is made in cold water it 
is called infusion. 
Decrepitation, the small and successive ex- 
plosions which take place when salts are 
exposed to heat to expel their water of 
crystallization. 
Desiccation (drying), the expelling or eva- 
porating humid matter from any substance 
by means of heat. 
Detonation, an explosion caused by the sud- 
den expansion of certain substances, when 
either a very rapid combination or decom- 
position takes place. 
Digestion, the slow action of a solvent upon 
any substance, often assisted by the heat 
of a sand-bath. 
Distillation, the operation which by means 
‘ of heat and moisture separates volatile 
matters from those which are fixed, or 
matters more or less volatile from one ano- 
ther. 
Effervescence, the escape of volatile matters 
from the mass of a fluid, which in their 
passage through cause a kind of ebulli- 
tion. 
Efflorescence. When solid or consistent bodies 
spontaneously become converted into 
powder, the surface appears covered with 
a white dust. r l his eifect is occasioned by 
the loss of the water of crystallization. 
Extract, the solid matter left behind when 
the watery parts are evaporated from a de- 
coction or infusion. 
Fixed, an epithet descriptive of such bodies 
as resist the action of heat, so as not to 
rise in vapour. It is opposed to volatile. 
Fulmination, a still more violent and sudden 
explosion than detonation. 
Fusion, the passing of a solid body to a fluid 
state by means of heat. 
Infusion, the extraction of resinous, gummy, 
or other matters, by the action of water in 
the common temperature of the atmo- 
sphere. 
Lixiviation, the process of separating by so- 
lution in water those matters which are 
soluble in any body from those which are 
insoluble; generally applied to the lixed 
residues of bodies for the purpose of ex- 
tracting the saline parts, which dissolve in 
the water, and afterwards crystallize on 
evaporation. 
Mixture, the aggregation or mechanical 
union of bodies which have no affinity or 
chemical combination. It is opposed to 
solution, where the particles ot the fluid 
and solid body are permanently combined. 
In mere mixtures, when set at rest, one 
part will commonly subside and form a 
sediment. 
Oxidation, the combination of any other 
body with oxygen. 
Precipitation, the effect which takes place in 
solution, in consequence of elective attrac- 
tion, when one matter is let fall to the bot- 
tom in consequence of the fluid particles 
combining with another. (See Affinity, 
above.) The product is also called a pre- 
cipitation. 
Reagent, a body which is brought in contact 
with another to promote the separation of 
its principles or constituent parts. The 
reagents are the immediate means of pre- 
cipitation. 
Rectification, the further purification of mat- 
ters by a second or third distillation or 
sublimation. 
Reduction, the bringing back the oxyds or 
calces of metals to the pure metallic state, 
by expelling the oxygen, which is gene- 
rally done by exposing the oxyd to the 
action of heat along with some matter con- 
taining carbon ; when the oxygen and car- 
bon go off in the form of carbonic acid gas, 
leaving the metal pure. 
Residuum (formerly called caput-Mortuum), 
that part of a body which remains after a 
part has been separated by an operation, 
such as distillation or sublimation. 
Saturation. Most bodies that have a che- 
mical affinity for each other will only unite 
in certain proportions. When, therefore, 
a fluid has dissolved as much of any sub- 
stance as it will dissolve, it is said to have 
reached the point of saturation. Thus, 
water will dissolve one quarter of its weight 
of common salt ; and if more is added, it 
’ will sink to the bottom in a solid state. 
Some fluids will dissolve more of certain 
’ substances when hot than when cold. Thus 
water when hot will dissolve a much larger 
quantity of nitre than when cold. 
Solution, the dispersion of the particles of a 
solid body in any fluid in so equal a man- 
ner, that the compound liquor shall be 
perfectly and permanently clear and trans- 
' parent. This happens when the particles 
of the fluid have an affinity or elective at- 
traction for the particles of the solid. 
When solid particles are only dispersed in 
a fluid by mechanical means, it is mixture, 
and the compound is commonly opaque 
and muddy. 
Sublimation is to dry matters what distilla- 
tion is to humid ones. It is the process by 
which the volatile are separated from the 
fixed parts of bodies by the application of 
heat alone without moisture. 
^ itrilieation, the conversion into glass of such 
substances as are capable of assuming that 
form. 
Volatilization, the reducing into vapour such 
substances as are capable of assuming that 
state. 
CHENOLEA, a genus of the order mono- ] 
gynia, in the pontandria class of plants. The 
calyx is globular, one-leafed, five-parted ; caps, 
one-celled, with one smooth seed. There is 
one species, a native of the Cape. 
CHENOPODIUM, goose-foot , or zeiid 
orach, a genus of the digynia order, in the I 
pentandria class of plants, and in the natural ■ 
method ranking under the 12th order, holo- 
raceae. The calyx is pentapliyllous and pen- 
tagonal ; no corolla ‘ one seed, lenticular, su- 
perior. There are 23 species, 13 of which j 
are natives of Britain. Most of them have j 
an aromatic smell. A species which epows 
near the Mediterranean is used by the Egyp- 
tians in sallads, on account of its saltish aro- j 
matic taste. From this plant kelp is made in 
other countries. The most remarkable are: ] 
1. Chenopodium ambroroides, or the oak 
of Cappadocia. These are easily propagated ' 
from seeds, and thrive best in a rich soil. 
2. Chenopodium bonus Henricus, or com- I 
mon English mercury, found growing natu- j 
rally in shady lanes in many places in Britain. 
It was formerly used as spinach, but is now 
disused, being greatly inferior. As an ar- ,] 
tide of the mate ia medica, it is ranked ; 
among the emollient herbs, but rarely used 
in practice. The 1 aves ,ure applied by the j 
country-people for healing slight wounds, 
cleansing old ulcers, and the like purposes, i 
'Fhe roots are given to sheep that have a 
cough. Goats and sheep are not fond of the ] 
herb ; cows, horses, and swine, refuse it. 
3. Chenopodium botrys, or the oak of 
Jerusalem, like that of Cappadocia, thrives 
best in a rich light earth, and may be easily 
propagated from seeds, as indeed ail the 
other species may. 
