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than an hour, the boiling should not ex-
ceed that time; the soap and silk being
put in about half an hour before the water
boils, and the silk frequently turned. A
less time would suffice for trames and or-
gan zines.

It is to the alterations which take place
when the boiling is too long continued,
that the impossibility of aluming silk in
the hot bath is owing; and the loss of
brilliancy when silk is dyed of colors
rather brown, for which a boiling heat is
necessar}'. — t/iiui. de C/iim. Vol. 65.



SIR H. DAVY S AGRICULTURAL CHEMISTRY.
(Conliiiutd from p. 164.)

To ascertain the primary elements of
the different vegetable principles, and
the proportions in which they are com-
bined, different methods of anal)'sis have
been adopted. The most simple are
their decomposition by heat, or their
formation into new products by combus-
tion.

When any vegetable principle is acted
on by a strong red heat, its elements be-
come newly arranged. Such of them as
are volatile are expelled in the gaseous
form; and are either condensed as fluids,
or remain permanently elastic. The fix-
ed remainder is either carbonaceous,
earthy, saline, alkaline, or metallic matter.

To make correct experiments on the
decomposition of vegetable substances by
heat, requires a complicated apparatus,
much time and labor," and all the re-
sources of the philosophical chemist; but



180



SIR H. DAVY S AGRICULTURAL CHE:»IISTRY.



such results as are useful to the agricul-
turist may be easily obtained.

The apparatus necessary, is a green
glass retort, attached by cement to a re-
ceiver, connected with a tube passing un-
der an inverted jar of known capacity,
filled with water. A given weight of
the substance is to be heated to redness
in the retort over a charcoal fire; the re-
ceiver is to be kept cool, and the process
continued as long as any elastic matter is
generated. The condcnsible fluids will



be formed of the composition of the sub-
stance. The proportions of the elements
in the greater number of the vegetable
substances which can be used as food,
have been already ascertained by philo-
sophical chemists, and have been stated
in the preceding pages; the analysis by
distillation may, however, in some cases,
be useful in estimating the powers of
manures in a manner that will be ex-
plained in a future lecture.

The statements of the composition of



collect in the receiver, and the fixed resi- 1 vegetable substances, quoted from MM.



duum will be found in the retort. The
fluid products of the distillation of vege-
table substances are principally water,
with some acetous and mucous acids and
empyreumatic oil, or tar, and in some
cases ammonia. The gassesare carbonic
acid gas, carbonic oxide, and carburetted
hydrogen; sometimes with olefiant gas,
and hydrogen; and sometimes, but more
rarely, with azote. Carbonic acid is the
only one of those gasses rapidly absorb-
ed by water; the rest are inflammable;
olefiant gas burns with a bright white
light; carburetted hydrogen with a light
like wax; carbonic oxide with a feeble,
blue flame. The properties of hydrogen
and azote have been described in the last
lecture. The specific gravity of carbonic
acid gas, is to that of air as 20.7 to 13.7,
and it consists of one proportion of c?r-
bon 11.4, and two of oxygen 30. The
specific gravity of gaseous oxide of car-
bon, is, taking the same standard, 13.2,
and it consists of one proportion of car-
bon, and one of oxygen. The specific
gravities of carburetted hydrogen and
olefiant gas are respectively S and 13;
both contain four proportions of hydro-
gen; the first contains one proportion,
the second two proportions of carbon.
If the weight of the carbonaceous resi-
duum be added to the weight of the fluids
condensed in the receiver, and they be^
subtracted from the whole weight of the
substance, the remainder will be the
weight of the gasseous matter.

The acetous and nmcous acids, and the
ammonia formed, are usually in very
small quantities; and by comparing the
proportions of water and charcoal with
the quantity of the gasses, taking into ac-
count their qualities, a general idea may



Gay Lussac and Thenard were obtained
by these philosophers by exposing the
substances to the action of heated hyper-
oxymuriate of potassa; a body that con-
sists of potassium, chlorine, and oxygen,
and which aff'orded oxygen to the carbon
and the hydrogen. Their experiments
were made in a peculiar apparatus, and
required great caution, and were of a very
delicate nature. It will not therefore be
necessary to enter upon any details of
them.

It is evident from the whole tenor of
the statements which have been made,
that the most essential vegetable sub-
stances consist of hydrogen, carbon, and
oxygen indifferent proportions, generally
alone, but in some few cases combined with
azotes. The acids, alkalies, earths, metallic
oxides, and saline compounds, though
necessary in the vegetable economy,
must be considered as of less importance,
particularly in their relation to agricul-
ture, than the other principles: and as it
appears from M. de Saussure's table, and
from other experiments, they differ in the
same species of vegetable when it is rais-
ed on different soils.

MM. Gay Lussac and Thenard have
deduced three propositions, which they
have called laivs, from. their experiments
on vegetable substances. The first is,
" that a vegetable substance is always
acid, whenever the oxygen it contains is
to the hydrogen in a greater proportion
than in water."

The second, "that a vegetable sub-
stance is always resinous or oily or
spirituous, whenever it contains oxygen
in a smaller proportion to the hydrogen
than exists in the water."

The third, "that a vegetable sub-



SIR H. DAVY S AGRICULTURAL CHEMISTRY.



181



stance is neither acid nor resinous; but is
either saccharine or mucilaginous, or
analagous to woody fibre or starch, when-
ever the oxygen or hydrogen* in it are in
the same proportions as in water."

New experiments upon other vegeta-
ble substances, besides those examined
by MM. Gay Lussac and Thenard, are
required before these interesting conclu-
sions can be fully admitted. Their re-
searches establish, however, the close
analogy between several vegetable com-
pounds differing in their sensible quali-
ties, and combined with those of other
chemists, offer simple explanations of
several processes in nature and art, by
which different vegetable substances are
converted into each other, or changed
into new compounds.

Gum and sugar afford nearly the same
elements by analysis: and starch differs
from them only in containing a little more
carbon. The peculiar properties of gum
and sugar must depend chiefly upon the
different arrangement, or degree of con-
densation of their elements; and it would
be natural to conceive from the composi-
tion of these bodies, as well as that of
starch, that all three would be easily con-
vertible one into the other; which is ac-
tually the case.

At the time of the ripening of corn,
the saccharine matter in the grain, and
that carried from the sap vessels into the
grain, becomes coagulated, and forms
starch. And in the process of malting,
the converse change occurs. The starch
of grain is converted into sugar. As
there is a little absorption of oxygen, and
a formation of carbonic acid in this case,
it is probable that the starch loses a little
carbon, which combines with the oxygen
to form carbonic acid; and probably the
oxygen tends to acidify the gluten of the
grain, and thus breaks down the texture
of the starch, gives a new arrangement
to its elements, and renders it soluble in
water.

Mr. Cruikshank, by exposing syrup to
a substance named phosphuret of lime,
which has a great tendency to decompose
water, converted a part of the sugar into
a matter analogous to mucilage. And
M. Kirchhoff, recently, has converted
starch into sugar by a very simple pro-



cess, that of boiling in very diluted sul-
phuric acid.

The proportions are 100 parts of starch,
400 parts of water, and 1 part of sulphu-
ric acid by weight. This mixture is to
be kept boiling for 40 hours; the loss of
water by evaporation being supplied by
new quantities. The acid is to be neu-
tralized by lime; and the sugar crystal-
lized by cooling. This experiment has
been tried with success by many persons.
Dr. Tuthill, from a pound and a half of
potato starch, procured a pound and a
quarter of crystalline brown sugar;
which he conceives possessed properties
intermediate between cane sugar, and
grape sugar.

It is probable that the conversion of
starch into sugar is effected merely by
the attraction of the acid for the elements
of sugar; for various experiments have
been made, which prove that the acid is
not decomposed, and that no elastic mat-
ter is set free; probably the color of the
sugar is owing to the disengagement, or
new combination of a little carbon, the
slight excess of which, as has been just
stated, constitutes the only difference
perceptible by analysis between sugar
and starch.

M. Bouillon la Grange, by slightly
roasting starch, has rendered it soluble in
cold water; and the solution evaporated
afforded a substance, having the charaters
of mucilage.

Gluten and albumen differ from the
other vegetable products, principally by
containing azote. When gluten is kept
Ions: in water it undergoes fermentation;
ammonia (which contains its azote) is
given off with acetic acid: and a fatty
matter, and a substance analogous to
woody fibre remain.

Extract, tannin, and gallic acid, when
their solutions are long exposed to air,
deposite a matter similar to woody fibre;
and the solid substances are rendered
analogous to woody fibre by slight roast-
ing; and in these cases it is probable that
part of their oxygen and hydrogen is
separated as water.

AH the other vegetable principles dif-
fer from the vegetable acids, in contain-
ing more hydrogen and carbon, or less
oxygen; many of them therefore are



182



DEFINITION OF TERMS.



easily converted into vegetable acids by
a mere substraction of some proportions
of hydrogen. The vegetable acids, for
the most part, are convertible into ench
other by easy processes. The oxalic
contains most oxygen, the acetic the
least: and this last substance is easily
formed by the distillation of other vege-
table substances, or by the action of the
atmosphere on such of them as are solu-
ble in water; probably by the mere com-
bination of oxygen with hydrogen and
carbon, or in some cases by the subtrac-
tion of a portion of hydrogen.
(To be Continued.)



Definition of Terms. — Letter J.

Japanning, is properly the art of var-
nishing and painting ornaments on wood,
in the same manner as it is done by the
natives of Japan, in the East Indies.
The substances which admit of being
japanned are almost every kind that are
dry and rigid, or not too flexible; as
wood, metals, leather, and paper, prepar-
ed for the purpose.

Wood and metals do not require any
other preparation, but to have their sur-
face perfectly even and clean; but leather
should be securely strained, either in
frames or on boards; as its bending, or
forming folds, would otherwise crack and
force off the coats of varnish. Paper
should be treated in the same manner,
and have a previous strong coat of some
kind of size; but it is rarely made the
subject of japanning till it is converted
into papier mache, or wrought by other
means into such form, that its original
state particularly with respect to flexi-
bility, is changed. One principal varia-
tion from the method formerly used in
japanning is the omitting any priming or
undercoat on the work to be japanned
In the other practice, such a priming
was always used; the use of which was
to save in the quantity of varnish, by
filling up the inequalities in the surface
of the substance to be varnished. But
there is a great inconvenience arising
from the use of it, that the japan coats
are constantly liable to be cracked, and
peeled off, by any violence, and will not
endure near so long as the articles which
are japanned without any such priming.



Of the nature of Japan grounds. —
When a priming is used, the work should
first be pre|)ared by being well smoothed
with fish skin, or glass-paper, and being
made thoroughly clean, should be brush-
ed over once or twice with hot size, di-
luted with two-thirds of water, if it is of
the common strength. The priming
should then be laid on as even as possi-
ble, and should be formed of a size, of a
consistency between the common kind
and glue, mixed with as much whiting
as will give it a sufficient body of color
to hide the surface of whatever it is laid
upon, but not more. This must be re-'
peated till the inequalities are completely
filled up, and then the work must be
cleaned off with Dutch rushes, and
polished with a wet rag. When wood or
leather is to be japanned, and no priming
is used, the best prejiaration is to lay two
or three coats of coarse varnish, compos-
ed in the following manner:

Take rectified spirits of wine one pint,
and of coarse seed-lac and resin each two
ounces; dissolve the seed-lac and resin
in the spirit, and then strain off" the var-
nish. This varnish, as well as all others
formed of the spirit of wine, must be laid
on in a warm place; and if it can be con-
veniently managed, the piece of work to
be varnished should be made warm like-
wise; and for the same reason, all damp-
ness should be avoided; for either cold
or moisture chills this kind of varnish,
and prevents its taking proper hold of
the substance on which it is laid. When
the work is so prepared, or by the prim-
ing with the composition of size and
vvhiting above described, the proper ja-
pan ground must be laid on, which is
much the best formed of shell-lac var-
nish, and the color desired, except white,
which requires a peculiar treatment;
and if brightness is wanted, then also
other means must be pursued.

The colors used with the shell-lac var-
nish may be any pigments whatever,
which give the tint of the ground desiied.
As metals never require to be under-
coated with whiting, they may be treat-
ed in the same manner as wood or lea-
ther.

Method of painting Japan work. —
Japan work ought properly to be painted



DEFINITION OF TERMS.



183



with colors in varnish; though for the
greater despatch, and in some very nice
work, in small, for the freer use of the
pencil, the colors are sometimes temper-
ed in oil, which should previously have
a fourth part of its weight of gum aninii
dissolved in it; or in default of that gum
sandarach, or gum maslich. When the
oil is thus used, it should be well diluted
with oil of turpentine, that the colors
may lie more evenly and thin; by which
means, fewer of the polishing or upper
coats of varnish become necessary. In
some instances, water-colors are laid on
grounds of gold, in the manner of other
paintings; and are best, when so used in
their proper ap])carance, without any var-
nish over them; and they are also some-
times so managed as to have the effect of
embossed work. The colors employed
in this way for painting, are best pre-
pared by means of isinglass size, correct-
ed by honey or sugar candy. The body,
of which the embossed work is raised,
need not, however, be tinged with the
exterior color, but may be best formed
of very strong gum water, thickened to
a proper consistence by bole armenian
and whiting in equal parts; which being
laid on the proper figure, and repaired
when dry, may be then painted with the
proper colors, tempered with the isinglass
size, or in the usual manner, with shell-
lae varnish.

Manner of varnishing Japan work.
—The finishing of japan work depends
on the laying on and polishing the outer
coats of varnish which are necessary, as
well in the pieces that have only one
simple ground of color as with those that
are painted. This is in general done
best with common seed-lac varnish, ex-
cept in these instances, and those occa-
sions, where particular methods are
deemed to be more expedient; and the
same reasons which decide as to the fitness
or impropriety of the varnishes, with re-
spect to the colors of the ground, hold
equally with regard to those of the paint-
ing. For where brightness is the most
material point, and a tinge of yellow will
injure it, seed-lac must give way to the
whiter gums; but where hardness and a
greater tenacity are most essential, it
must be adhered to; and where both are



so necessary, that it is proper one should
give way to the other in a certain degree
reciprocally, a mixed varnish must be
adopted. T[iis mixed varnish, as we
have already observed, should be made
of the picked seed-lac. The common
seed-lac varnish, which is the most use-
ful preparation of the kind hitherto in-
vented, may be thus made. Take of seed-
lac three ounces, and put it into water to
free it from the sticks and filth that are
frequently intermixed with it, and which
must be done by stirring it about, and
then pouring off the water, and adding
fresh quantities, in order to repeat the
operation till it is freed from all impuri-
ties, as is very effectually done by this
means. Dry it then and powder it
grossly, and put it with a pint of rectified
spirit of wine, into a bottle, of which it
will not fill above two-thirds. Shake the
mixture well together, and place the bot-
tle in a gentle heat, till the seed-lac ap-
pears to be dissolved; the shaking being
in the mean time repeated as often as
may be convenient; and then pour off all
that can be obtained clear by this method,
and strain the remainder through a coarse
cloth. The varnish thus prepared, must
be kept for use in a bottle well stopped.
When the spirit of wine is very strong
it will dissolve a greater proportion of
the seed-lac; but this quantity will satu-
rate the common, which is seldom of a
strength sufficfent to make varnishes in
perfection.

As the chilling which is the most in-
convenient accident attending varnishes
of this kind, is prevented or produced
more frequently, according to the strength
of the spirit, we shall, therefore, take
this opportunity of showing a method by
which weaker rectified spirits may with
great ease at any time be freed from the
phlegm, and rendered of the first degree
of strength. Take a pint of the com-
mon rectified spirit of wine, and put it
into a bottle, of which it will not fill
above three parts; add to it half an ounce
of pearl-ashes, salt of tartar, or any other
alkaline salt, heated red-hot and powder-
ed as well as it can be without much loss
of its heat. Shake the mixture frequent-
ly for the space of half an hour; before
which lime, a great part of the phlegm



184



DEFINITION OF TERMS.



will be separated from the spirit, and will
appear, together with the undissolved
part of the salts, in the bottom of the
bottle. Let the spirit be poured off or
freed from the phlegm and the salts, by
means of a tcitorium, or separating fun-
nel; and let half an ounce of the pearl-
ashes, heated and powdered as before, be
added to it, and the same treatment re-
peated. This may be done a third time,
if the quantify of phlegm separated by the
addition of the pearl-ashes appears con-
siderable. An ounce of alum reduced
to powder, and made hot, but not burnt,
must then be put into the spirit, and suf-
fered to remain some hours, the bottle
being frequently shaken; after which the
spirit, being poured off from it, will be
fit for use.

The addition of the alum is necessary
to neutralize the remains of the alkaline
salt, which would otherwise greatly de-
prave the spirit, with respect to varnishes
and lacquer where vegetable colors are
concerned, and must consequently ren-
der another distillation necessary. The
manner of using the seed-lac, or white
varnish, is the same, except with regard
to the substance used in polishing; which,
where a pui;e white of a great clearness
of other colors is in question, should be
itself white; whereas the browner sorts
of polishing dust, as being cheaper, and
doingthe business with greater despatch,
may be used in other cases. The pieces
of work to be varnished, should be placed
near a fire or in a room where there is a
stove, and made perfectly dry; and then
the varnish may be rubbed over them by
the proper brushes made for that purpose,
beginning in the middle, and passing the
brush to one end, and then with another
stroke from the middle, passing it to the
other. But no part should be crossed, or
twice passed over, in forming one coat,
where it can be possibly avoided. When
one coat is dry, another must be laid over
it; and this must be continued at least
five or six times, or more, if on trial
there is not sufficient thickness of var-
nish to bear the polish, without laying
bare the painting or ground color under-
neath. When a sufficient number of
coats is thus laid on, the work is fit to be
polished: which must be done in com-



mon cases by rubbing it with a rag
dipped in tripoli or rotten-stone, finely
powdered ; but towards the end of the
rubbing, a little oil of any kind should
be used along with the powder; and
when the work appears sufficiently bright
and glossy, it should be well rubbed with
the oil alone, to clean it from the pow-
der, and give it a still brighter lustre.

Jatropha, the cossada plant, a genus
of the monadelphia order, in the monoe-
cia class of plants, and in the natural
method ranking under the thirty-eighth
order, tricocca. There are nine species,
of which the most remarkable are — 1.
The curcas, or English physic nut. 2.
The gossypifolia, cotton leaved jatropha.

3. The multifida, or French physic nut.

4. The manihot or bitter cassada, 5. The
janiphii,or sweet cassada. 6. The elasti-
ca. The root of the bitter cassada has no
fibrous or woody filaments in the heart,
and neither boils nor roasts soft. The
sweet cassada has all the opposite quali-
ties. The bitter, however, may be der
prived of its noxious qualities (which re^
side in the juice) by heat, Cassada bread
is therefore made of both the bitter and
sweet. Thescrapings of fresh bittercassada
are successfully applied to ill disposed
ulcers. Cassada roots yield a great quan-
tity of starch, which the Brazilians ex-
port in little lumps, under the name of
tapioca. A fermented drink called ouycau,
is prepared with this root. West India
potatoes and molasses. The sixth species
is the hevea guianensis, of Aublet, "or
tree that yields the elastic resin caout-
chouc (India rubber.)

Jelly, in chemistry. If we press
out the juice of ripe blackberries,
currents, and many other fruits, and
allow it to remain for some time in a
state of rest, it partly coagulates into a
tremulous soft substance, well known by
the name of jelly. If we pour off the
incoagulated parts, and wash the coagulum
with a small quantity of water, we ob-
tain jelly approaching to a state of pu-
rity. In this state it is nearly colorless,
unless tinged by the peculiar coloring
matter of the fruit ; it has a pleasant
taste, and a tremulous consistency. It is
scarcely soluble in cold water, but very
soluble in hot water, and when the solu-



DEFINITION OF TERMS.



185



tion cools, it again coagulates into the
form of a jelly. When long boiled, it
loses the property of gelatinizing by cool-
ing, and becomes analogous to mucilage.
This is the reason that in making current
jelly or any other jelly, when the quan-
tity of sugar added is not sufficient to
absorb all the watery parts of the fruit,
and consequently it is necessary to con-
centrate the liquid by long boiling, the
mixture often loses the property of coa-
gulating, and the jelly, of course, is
spoiled.

Jelly combines readily with alkalies.
Nitric acid converts it into oxalic acid,
without separating any azotic gas. When
dried it becomes transparent. When
distilled it affords a great deal of pyro-
mucous acid, a small quantity of oil, and
scarcely any ammonia. Jelly exists in
all the acid fruits, as oranges, lemons,
gooseberries, &c. If the juice of these
fruits is allowed to gelatinize, and then
poured upon a scarce, the acid gradually
filtrates through and leaves the other;
which may be washed with a little cold
water, and allowed to dry. Its bulk gra-
dually diminishes, and it concretes into a
hard transparent brittle mass, which pos-
sesses most of the properties of gum.
Perhaps, then, jelly is merely gum com-
bined with vegetable acid.

Joint tenants, are those that come to



Online LibraryD. PeirceObserver and record of agriculture, Science and art (Volume v.1) → online text (page 33 of 35)