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very extensive researches by Debus, Higgins, and especially by Schunk. The
latest papers on madder have been published by Wolff and Strecker, whose
formulae are quoted in the following abstract.

ALIZARIN. The aqueous decoction of madder is precipitated by sulphuric
acid, and the precipitate washed and boiled with sesquichloride of aluminum,
which dissolves the red pigments ; an insoluble brownish residue remaining
behind. The solution, when mixed with hydrochloric acid, yields a precipi-
tate consisting chiefly of alizarin, however, still contaminated with purpurin.
The impure alizarin thus obtained may be farther purified by again throwing

1 Mem. of the Chem. Soc. vol. iii. p. 464.



478 RED AND YELLOW DYES.

down the alcflholic solution with hydrate of alumina, and boiling the preci-
pitate with a concentrated solution of soda, which leaves a pure compound
of alumina and alizarin behind. From this the alizarin is separated by
hydrochloric acid, and re-crystallized from alcohol. Pure alizarin crystal-
lizes in splendid red prisms, which may be sublimed. It is but slightly solu-
ble in water and in alcohol, but dissolves in concentrated sulphuric acid with
a deep red colour. On addition of water, the colouring matter is re-precipi-
tated unchanged. It is also soluble in alkaline liquids, to which it imparts
a magnificent purple colour. It is insoluble in cold solution of alum. Ali-
zarin is the chief colouring matter of madder ; it contains C 20 H 6 6 -|-4HO, and
is a feeble acid ; but a few definite compounds with mineral oxides have been
prepared, among which a lime-compound, C 20 H 6 6 ,3Ca04-3HO, may be
quoted. The action of nitric acid upon alizarin gives rise to the formation
of oxalic acid and phthalic acid, a substance which will again be men-
tioned among the products of decomposition of naphthalin.

C M H 6 6 +2HO+80 = 2(C,O a> HO) + C ie H 6 O g

Alizarin. Phthalic acid.

PURPURIN. Madder is allowed to ferment and then boiled with a strong
solution of alum. The solution, when mixed with sulphuric acid, yields a
red precipitate, which is purified by re-crystallization from alcohol. Purpurin
thus obtained crystallizes in red needles, which contain C 18 H 6 6 -j-2HO, i. e.,
2 eq. of carbon less than alizarin. When treated with nitric acid, purpurin,
like alizarin, furnishes oxalic and phthalic acids. Purpurin likewise con-
tributes to the tinctorial properties of madder, but less so than alizarin.
Together with alizarin and purpurin, several other substances occur in
madder, among which may be noticed an orange pigment, rubiacin, convertible
by oxidizing agents into a peculiar acid, rubiacic acid, a yellow pigment,
xanthin, a bitter principle, rubian, sugar, pectic acid, and several resins, &c.

Garancin is a colouring material, which is produced by the action of sul-
phuric acid upon madder. This substance possesses a higher tinctorial power
than madder itself.

The beautiful Turkey red of cotton cloth is a madder-colour ; it is given by
a very complicated process, the theory of which is not perfectly elucidated.
An abstract of it will be found in Prof. Graham's " Elements of Chemistry."

SAFFLOWER. This substance contains a yellow and a red colouring matter,
the latter being insoluble in water, but soluble in alkaline liquids. The saf-
flower may be exhausted with water acidulated with acetic acid, and the
solution mixed with acetate of lead, and filtered from the dark-coloured
impure precipitate. The lead-compound of the yellow pigment may then be
thrown down by addition of ammonia, and decomposed by sulphuric acid.
In its purest form the yellow matter forms a deep yellow, uncrystallizable,
and very soluble substance, very prone to oxidation. In its lead-compound
it has probably the composition C^H^O^.

The red matter or carthamin is obtained from the residual safflower by a
dilute solution of carbonate of soda ; pieces of cotton wool are immersed in
the liquid, and acetic acid gradually added. The dried cotton is then digested
in a fresh quantity of the alkaline solution, and the liquid supersaturated
with citric acid, which throws down the carthamin in carmine-red flocks. It
forms, when pure and dry, an amorphous, brilliant, green powder, nearly
insoluble in water, but soluble in alcohol with splendid purple colour. It
contains C 14 H 8 7 .

Brazil-wood and Logwood give red and purple infusions, which are largely
used in dyeing ; the colouring principle of logwood is termed hematoxylin,



RED AND YELLOW DYES. 479

and has been obtained in crystals. This substance contains C 40 H 7 16 -f-8HO
Acids brighten these colours, and alkalis render them purple or blue.

Among yellow dyes, quercitron-bark, fustic-wood, and saffron may be men-
tioned, and also turmeric ; these all give yellow infusions to water, and furnish
more or less permanent colours.

Pwre& or Indian yellow, a body of unknown origin, used in water-colour
painting, according to the researches of Stenhouse and Erdmann, is a com-
pound of magnesia with a substance termed purreic or euxanthic acid. The
latter, when pure, crystallizes in nearly colourless needles, sparingly soluble
in cold water, and of sweetish bitter taste. It forms yellow compounds with
the alkalis and earths, and is decomposed by heat with production of a
neutral crystalline sublimate, pnrrenone or euxanthone. Purreic acid contains
C 40 Hjg0 2 i, purrenone C, 3 H 4 4 . By the action of chlorine, bromine, and nitrio
acid, a series of substitution-products are formed.



Certain of the products of the action of nitric acid upop aloes resemble
very much some of the derivatives of indigo, without, however, it seems,
being identical with them. Powdered aloes, heated for a considerable time
with excess of moderately strong nitric acid, yields a deep red solution, which
deposits on cooling a yellow crystalline mass. This, purified by suitable
means, constitutes chrysammic acid; it crystallizes in golden-yellow scales,
which have a bitter taste, and are but sparingly soluble in water. Its potassa-
salt has a carmine-red tint, and exhibits a green metallic lustre, like that of
murexide. The formula of chrysammic acid is not perfectly established. It
is probably C 14 HN 2 11 ,HO. Like picric acid, it yields with chloride of lime,
chloropicrin. The mother-liquor from which the chrysammic acid has been
deposited contains a second acid, the chrysolepic, which Also forms golden-
yellow, sparingly soluble, scaly crystals. The potassa-salt forms small,
yellow prisms, of little solubility. It explodes by heat. Chrysolepic acid
contains C, 2 H 2 N 3 0, 3 ,HO ; it is isomeric and possibly identical with picric acid.

To these may be added the styphnic acid recently described by MM.
Boettger and Will, produced by the action of nitric acid of sp. gr. 1-2 upon
assafoztida and several v&er gum-resins and extracts. Purree, when treated
with excess of nitric acid, likewise yields styphnic acid. It crystallizes,
when pure, in slender, yellowish-white prisms, sparingly soluble in water,
readily dissolved in alcohol and ether. It has a purely astringent taste,
and stains the skin yellow. By gentle heat it melts, and on cooling becomes
crystalline ; suddenly and strongly heated, it burns like gunpowder. It also
furnishes chloropicrin. The salts of this substance mostly crystallize in
orange-yellow needles, and explode with great violence by heat. Styphnio
acid contains C, 2 H 2 N 3 15 ,HO, i. e., picric acid-f-2 eq. of oxygen. It may be
viewed as a nitro-substitute of the same acid, C 12 H 5 3 ,HO, which, by the in-
troduction of chlorine in the place of hydrogen, furnishes chloroniceic acid
(see page 463).

Hypothetical niceic acid C 12 H 5 ,0 3 ,HO

Chlovoniceic acid C 12 (H 4 C1)0 3 ,HO

Trinitroniceic acid C 12 H 2 (N0 4 )30 S ,HO.



OILS AND FATS.



SECTION VII.

OILS AND FATS.



THE oils and fats form an interesting and very natural group of substances,
which have been studied with great success. The vegetable and animal fats
agree so closely in every respect, that it will be convenient to discuss them
under one head.

Oily bodies are divided into volatile and fixed: the former are capable of
"being distilled without decomposition, the latter are not. When dropped or
spread upon paper, they all produce a greasy stain ; in the case of a vola-
tile oil, this stain disappears when the paper is "warmed, which never happens
with a fixed fatty substance. All these bodies have an attraction, more or
less energetic, for oxygen : this in some cases reaches such a height as to
occasion spontaneous inflammation, as in the instance of large masses of cot-
ton or flax moistened with rape ojr linseed oil. The effect of this absorption
of oxygen leads to a farther classification of the fixed oils into drying and
non-drying oils, or those which become hard and resinous by exposure to air,
and those which thicken slightly, become sour and rancid, but never solidify.
To the first class belong the oils used in painting, as linseed, rape, poppy-
seed, and walnut ; and to the second, olive and palm-oils, and all the oils and
fats of animal origin. The parts of plants which contain the largest quanti-
ties of oil are, in general, the seeds. Olive-oil is, however, obtained from the
fruit itself. The leaves of many plants are varnished on their upper surface
with a covering of waxy fat. Among the natural orders, that of the cruciferce
is conspicuous for the number of oil-bearing species.

The fixed oils in general have but feeble odour, and scarcely any taste ;
whenever a sapid oil or fat is met with, it is invariably found to contain some
volatile oily principle, as in the case of common butter. They are all insolu-
ble in water, and but slightly soluble in alcohol, with the exception of castor-
oil ; in ether and in the essential oils, on the other hand, they dissolve in
large quantity.

The consistence of these substances varies from that of the thinnest olive-
oil to that of solid, compact suet; and this difference proceeds from the vari-
able proportions in which the proximate solid and fluid fatty principles are
associated in the natural product. All these bodies may, in fact, by mere
mechanical means, or by the application of a low temperature, be separated
into two, or sometimes three, different substances, which dissolve in, or mix
with each other, in all proportions. Thus, olive oil exposed to a cold of
40 (4-5C) deposits a large quantity of crystalline solid fat, which may be
separated by filtration and pressure ; this is termed margarirt, from its pearly
aspect. That portion of the oil which retains its fluidity at this, or even an
inferior degree of cold, has received the name olcin or elain. Again, a solid
animal fat may, by pressure between folds of blotting-paper, be made much
harder, more brittle, and more difficult of fusion. The paper becomes im-
pregnated with a permanently fluid oil, or olein, while the solid part is found
to consist of a mixture of two solid fats, one resembling the margarin of olive-



OILS AND FATS. 481

oil, and the other having a much higher melting-point, and other properties
Which distinguish it from that substance ; it is called stearin.

These remarks apply to all ordinary oils and fats : it is, however, by no
means proved that the olein and margarin of all vegetable and animal oils
are identical; it is very possible that there may be essential differences
among them, more especially in the case of the first-named substance.

Fixed fatty bodies, in contact with alkaline solutions at a high tempera-
ture, undergo the remarkable change termed saponification. When stearin,
margarin, or olein, are boiled with a strong solution of caustic potassa or
soda, they gradually combine with the alkali, and form a homogeneous,
viscid, transparent mass, or soap, freely soluble in warm water, although in-
soluble in saline solutions. If the soap so produced be afterwards decom-
posed by the addition of an acid, the fat which separates is found completely
changed in character ; it has acquired a strong acid reaction when applied
in a melted state to test-paper, and it has become soluble with the greatest
facility in warm alcohol ; it is in fact a new substance, a true acid, capable
of forming salts, and a compound ether, and has been generated out of the
elements of the neutral fat under the influence of the base. Stearin, when
thus treated, yields slearic acid, margarin gives margaric add, olein gives
oleic acid, and common animal fat, which is a mixture of the three neutral
bodies, affords by saponification by an alkali and subsequent decomposition
of the soap, a mixture of the three fatty acids in question. These bodies
are not, however, the only products of saponification ; the change is always
accompanied by the formation of a very peculiar sweet substance, called
glycerin, which remains in the mother-liquor from which the acidified fat has
been separated. The process of saponification itself proceeds with perfect
facility in a close vessel ; no gas is disengaged ; the neutral fat, of whatso-
ever kind, is simply resolved into an alkaline salt of the fatty acid, or soap,
and into glycerin. 1

STEARIN AND STEARIC ACID. Pure animal stearin is most easily obtained
by mixing pure mutton-fat, melted in a glass flask, with several times ita
weight of ether, and suffering the whole to cool. Stearin crystallizes out,
while margarin and olein remain in solution. The soft pasty mass may then
be transferred to a cloth, strongly pressed, and the solid portion still farther
puritied by re-crystallization from ether. It is a white friable substance, in-
soluble in water, and nearly so in cold alcohol ; boiling spirit takes up a
small quantity. Boiling ether dissolves it with great ease, but when cold
retains only ^t of its weight. The melting-point of pure stearin, which is
one of its most important physical characters, may be placed at about 130
(54 C -5C).

When stearin is saponified, it yields, as already stated, glycerin and etearic
acid. The latter crystallizes from hot alcohol in milk-white needles, which
are inodorous, tasteless, and quite insoluble in water. It dissolves in its
own weight of cold alcohol, and in all proportions at a boiling heat ; it is
likewise soluble in ether. Alkaline carbonates are decomposed by stearic
acid. Exposed to heat, it fuses, and at a higher temperature, if air be ex-
cluded, volatilizes unchanged. The melting-point of stearic acid is about
158 (70C).

MARGARIN AND MARGARIC ACID. The ethereal mother-liquor from which
stearin has separated in the process just described yields on evaporation a
soft-solid mixture of margarin and olein with a little stearin. By compres-

1 We are indebted to M. Chevreul for the first series of scientific researches on the fixed
oile and fats, and on the theory of saponification. These admirable investigations are detailed
in the early volumes of the ' Annales de Chimie et de Physique," and were afterwards pub-
lished in a Beparat* form in 1823, under the title of ; ' Rccherches chimiquet tur lee Corps grm
<FOrit/ine animate."
41



482 OILS AND FATS.

sion between folds of blotting-paper, and re-solution in ether, it is rendered
tolerably pure. Iii this state margarin very mvich resembles stearin ; it is
however, more fusible, melting at 116 (46-GC), and very much more solu-
ble in cold ether. By saponification it yields glycerin and margaric acid.
The properties of this last-named substance resemble in the closest manne?
those of stearic acid ; it is different in composition, however, more soluble
in cold spirit, and has a lower melting-point, viz., 140 (60C) or there-
abouts. Its salts also resemble those of stearic acid.

A more or less impure mixture of stearic and margaric acids is noia
very extensively used as a substitute for wax and spermaceti in the manu-
facture of candles. It is prepared by saponifying tallow by lime, decom-
posing the insoluble salt so formed by boiling with dilute sulphuric acid, and
then pressing out the fluid or oily portion from the acidified fat.

The solid part of olive-oil is said to be a definite compound of true mar-
garin and olein, inasmuch as its melting-point, 68 (20C), is constant ; it
gives by saponification a mixture of margaric and oleic acids.

OLEIN AND OLEIC ACID. It is doubtful whether a perfectly pure olein has
yet been obtained ; the separation of the last portions of margarin, with
which it is always naturally associated, is a task of extreme difficulty. Any
fluid oil, animal or vegetable, which has been carefully decolorized, and
filtered at a temperature approaching the freezing-point of water, may be
taken as a representative of the substance. Oleic acid much resembles olein
in physical characters, being colourless and lighter than water, but it has
usually a distinct acid reaction, a sharp taste, and is miscible with alcohol
in all proportions. When submitted to the action of nitric acid, it yields
almost the whole series of acids, of which formic, acetic, propionic, butyric,
&c., are members, and which has been mentioned in a previous section of
this work (see page 395).

When stearic or margaric acid, or ordinary animal fats, are exposed to
destructive distillation, they yield margaric acid, a fatty body incapable of
saponification, termed marffctrone, a liquid carbide of hydrogen, and various
permanent gases. The neutral fats furnish besides an extremely pungent
and even poisonous, volatile principle, called acrolein, described farther on.

In the manufacture of ordinary soaps both potassa and soda are used ; the
former yielding soft, and the latter hard soaps. Animal and vegetable fats
are employed indifferently, and sometimes resin is added.

Composition of the preceding Substances. The following are the formulce at
present assigned to the fatty acids in question : they are chiefly founded on
investigations made at Giessen.

Stearic acid ................................... C 6g fT 66 5 ,2HO

Margaric acid ................................ C^E^



Margaric is thus seen to differ from stearic acid in containing 1 eq. of oxy-
gen more, and stearic acid can actually be converted into margaric by the
action of oxidizing agents. Stearic acid is bibasic, and in its crystallized
state contains 2 eq. of water. Margaric acid, as represented by the above
formula, is likewise bibasic, but many chemists consider it as a monobasic
acid C^HggO^HO; its bibasic nature being, in fact, by no means so we'.l
established as that of stearic acid. The subject requires farther examina-
tion, especially since an opinion has lately been expressed, that stearic and
margaric acids are isomeric modifications of the same acid. 1

1 According to Huntz, mnnrarie ncid is a mixture of rtearic and prJmitio acid?, and tli?t
one part of stearic acid mixed with 9-10 parts of palmitic arid (melting at 144; 62-2C), pro-
duced a compound fusing at 140 (0C), and possessing all the properties and ultimate com-
position of margnric ncid. Moreover, when mar^aric acid obtained from mutton-fat was acted
OH by acetate of baryta, the first precipitate gave an acid melting at 135'5 (57 C), and solili-



OILS AND FATS. 483

acid from almond-oil, butter, and beef-suet, gave results agreeing
well, and leading to the formula 035113303,110, the oleic acid of goose-
r,nd olive-oil, having the same composition. Former researches had led
to different results which are explained by the extreme proneness to oxida-
tion of the substance itself. The oleic acid obtained from linseed-oil appears
to differ from the preceding substance; its analysis having led to the for-
mula C^H^O^HO. (?)

Margarone probably contains C^HggO, or margaric acid minus 1 eq. of
carbonic acid.

The composition of stearin, margarin, and oleine is most safely deduced
from a comparison of that of the acids to which they give rise, and of gly-
cerin.

Margaric, stearic, and oleic acids have many properties in common ; their
salts much resemble each other, those of the alkalis being soluble in pure
water when warm, but not in saline solution. A large quantity of cold water
added to an alkaline margarate or stearate occasions the separation of a
crystalline, insoluble acid salt. The margarates, stearates, and oleates of
lime, baryta, and the oxides of the metals proper are insoluble in water.
They are easily obtained by double decomposition, and in some few cases by
direct action on the neutral fat. A solution of soap in alcohol is sometimes
used as a test for the presence and quantity of lime, &c., in waters under
examination (see page 241).

GLYCERIN. This substance is very readily obtained by heating together
olive or other suitable oil, protoxide of lead, and water, as in the manufacture
of common lead-plaster ; an insoluble soap of lead is formed, while the gly-
cerin remains in the aqueous liquid. The latter is treated with sulphuretted
hydrogen, digested with animal charcoal, filtered, and evaporated in vacua
at the temperature of the air. In a pure state, glycerin forms a nearly colour-
less and very viscid liquid, of sp. gr. 1-27, which cannot be made to crystal-
lize. It has an intensely sweet taste, and mixes with water in all propor-
tions ; its solution does not undergo the alcoholic fermentation, but when
mixed with yeast and kept in a warm place, it is gradually converted into
propionic acid (see page 377). Glycerin has neither basic nor acid proper-
ties. Exposed to heat, it volatilizes in part, darkens, and becomes destroyed,
one of its products of destruction being a substance possessing a most power-
fully penetrating odour, which is called acrolein (see page 345). Nitric acid
converts it into oxalic acid.

Glycerin is composed of C 6 H 8 6 .

Glycerin combines with the elements of sulphuric acid, forming a compound
acid, the sulphogly eerie, C 6 H 7 6 ,2S0 3 ,HO, which gives soluble salts with lime,
baryta, and protoxide of lead. 1

PALM AND COCOA OILS. These substances, which at the common tempera-
ture of the air have a soft-solid or buttery consistence, are now largely con-
sumed in this country. Palm-oil is the produce of the Elais guianensis, and
comes chiefly from the coast of Africa. It has, when fresh, a deep orange-
red tint, and a very agreeable odour ; the colouring matter, the nature of

fied without crystallizing ; the other one, after repeated crystallization, melted at 142-7 (61-5
C). crystallized in needles, and exhibited the properties of palmitic acid. R. B.

1 Glycerin has been combined with acids. To effect this, the acid is mixed with the glyce-
rin, and a current of hydrochloric acid passed through the mixture for several hours. This
Is set aside for periods, varying from a few days to several weeks. The hydrochloric acid is
saturated by carbonate of soda, and then washed repeatedly.

These compounds are oleaginous, nearly or quite insoluble in water, do not unite with,
carbonated, but are slowly decomposed by caustic alkali, the glycerin separating unaltered.

Acetate of glycerin (acetine) has the appearance of a limpid, colourless oil, of a taste, at
first, sweet, then sharp, the odour of acetic ether, and is volatile, without decomposition.

Valerate of glycerin (valerene) resembles phocenine, with which it should be identical.

Benzoate of glycerin (benzoicine) has an aromatic and peppery taste. R. B.



484 OILS AND FATS.

which is unknown, is easily destroyed by exposure to light, especially at s
high temperature, and also by oxidizing agents. The oil melts at 80 (26 -6
C). By cautious pressure it may be separated into a fluid olein and a solid
substance, palmitin, which, when purified by crystallization from hot ether,
is perfectly white, fusible at 118 (47 -8C), soluble to a small extent only in
boiling alcohol, and convertible by saponification into palmitic acid. The latter
resembles in the closest manner margaric acid, and has the same melting-
point; it differs in composition, however, containing H 32 C 31 3 ,HO. By keep-
ing, palm-oil seems to suffer a change similar to that produced by saponifi-
fication; in this state it is found to contain traces of glycerin, and a
considerable quantity of oleic acid, together with a solid fatty acid, first
supposed to be margaric, which is probably palmitic acid. The oil becomes
harder and rancid, and its melting-point is raised at the same time. Cocoa-
oil, extracted from the kernel of the common cocoa-nut, is white, and has a
far less agreeable smell than the preceding. It contains olein and a solid fat,
often used as a substitute for tallow in making candles, which by saponifica-
tion gives a crystallizable fatty acid, cocinic acid, having the usual properties



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