_Rhubarb_; F. _Rhubarbe_; G. _Rhabarber_.
=Botanical Origin=—No competent observer, as far as we know, has ever
ascertained as an eye-witness the species of Rheum which affords the
commercial rhubarb. Rheum officinale, from which it seems, at least
partly, derived is the only species yielding a rootstock which agrees
with the drug.
_Rheum officinale_ Baillon is a perennial noble plant resembling the
Common Garden Rhubarb, but of larger size. It differs from the latter
in several particulars: the leaves spring from a distinct crown rising
some inches above the surface of the ground; they have a subcylindrical
petiole, which as well as the veins of the under side of the lamina is
covered with a pubescence of short erect hairs. The lamina, the outline
of which is orbicular, cordate at the base, is shortly 5-to 7-lobed,
with the lobes coarsely and irregularly dentate; it attains 4 to 4½
feet in length and rather more in breadth. The first leaves in spring
display before expanding the peculiar metallic red hue of copper.
The plant was discovered in South-eastern Tibet, where it is said to be
often cultivated for the sake of its medicinal root; but it is supposed
to grow in various parts of Western and North-western China, whence
the supplies of rhubarb are derived. It was obtained by the French
missionaries about the year 1867 for Dabry, French Consul at Hankow,
who transmitted specimens to Dr. Soubeiran of Paris. From one of these
which flowered at Montmorency in 1871, a botanical description was
drawn up by Baillon.[1801]
To what extent the rhubarb of commerce is derived from this plant is
not known. But that the latter may be a true source of the drug is
supported by the fact, that there is at least no important discrepancy
between it and the accounts and figures, scanty and imperfect though
they are, given by Chinese authors and the old Jesuit missionaries; and
still more by the agreement in structure which exists between its root
and the Asiatic rhubarb of commerce.
We have engaged in 1873 Mr. Rufus Usher at Bodicott (see below, p. 500)
to cultivate Rheum officinale, which is there admirably succeeding;
but it must be granted that as yet the root, notwithstanding the most
careful preparation in drying it, is far from displaying the rich
yellow of the commercial drug. It is most obviously marked on the other
hand with the characteristic ring of stellate markings, which we have
constantly observed in many roots of Rheum officinale cultivated by us
at Clapham Common near London, as well as at Strassburg or, by other
observers, at Paris.
_Rheum palmatum_ L., a species known as long as 1750, has always been
supposed to yield also rhubarb, and this has again been asserted by the
Russian Colonel Przewalski, who observed in 1872 and 1873 that plant
in the Alpine parts of Tangut round the Lake Kuku-nor, in the Chinese
province of Kansu, in 36°-38° North Lat.—Rheum palmatum has been
frequently cultivated in Russian Asia and in many parts of Europe since
the last century, but without producing a root agreeing with Chinese
rhubarb. Now, Przewalski states that from this species the drug under
notice is largely collected along the river Tetung-gol (or Datung-ho),
a tributary of the upper Hoang-ho, northward of the Kuku-nor. Specimens
of that root were largely brought to St. Petersburg by Przewalski, but
Dragendorff expressly points out in his _Jahresbericht_ for 1877 (p.
78) that it is _dissimilar_ to true rhubarb.
[1801] _Adansonia_, x. 246; _Association Française pour l’avancement
de la Science_, Comptes Rendus de la 1ʳᵉ Session, 1872. 514-529. pl.
x.—The figure which is reproduced in Lanessan’s French translation of
the _Pharmacographia_, ii. (Paris, 1878) 210, gives a good idea of the
highly ornamental character of Rheum officinale.
=History=[1802]—The Chinese appear to have been acquainted with the
properties of rhubarb from a period long anterior to the Christian
era, for the drug is treated of in the herbal called _Pen-king_,
which is attributed to the Emperor Shen-nung, the father of Chinese
agriculture and medicine, who reigned about 2700 B.C. The drug is named
there _Huang-liang_, yellow, excellent, and _Ta-huang_, the great
yellow.[1803] The latter name also occurs in the great Geography of
China, where it is stated that rhubarb was a tribute of the province
Si-ning-fu, eastward of Lake Kuku-nor,[1804] from about the 7th to the
10th centuries of our era.
As regards Western Asia and Europe, we find a root called ῤᾶ or ῤῆον,
mentioned by Dioscorides as brought from beyond the Bosphorus. The same
drug is alluded to in the fourth century by Ammianus Marcellinus,[1805]
who states that it takes its name from the river Rha (the modern
Volga), on whose banks it grows. Pliny describes a root termed
_Rhacoma_, which when pounded yielded a colour like that of wine but
inclining to saffron, and was brought from beyond Pontus.
The drug thus described is usually regarded as rhubarb, or at least
as the root of some species of _Rheum_, but whether produced in the
regions of the Euxine (Pontus), or merely received thence from remoter
countries, is a question that cannot be solved.
It is however certain that the name _Radix pontica_ or _Rha ponticum_,
used by Scribonius Largus[1806] and Celsus,[1807] was applied in
allusion to the region whence the drug was received. Lassen has shown
that trading caravans from Shensi in Northern China arrived at Bokhara
as early as the year 114 B.C. Goods thus transported might reach Europe
either by way of the Black Sea, or by conveyance down the Indus to
the ancient port of Barbarike. Vincent suggests[1808] that the _rha_
imported by the first route would naturally be termed _rha-ponticum_,
while that brought by the second might be called _rha-barbarum_.
We are not prepared to accept this plausible hypothesis. It receives no
support from the author of the Periplus of the Erythrean Sea (_circa_
A.D. 64), whose list of the exports of Barbarike[1809] does not include
rhubarb; nor is rhubarb named among the articles on which duty was
levied at the Roman custom-house of Alexandria (A.D. 176-180).[1810]
The terms _Rheum barbarum_ vel _barbaricum_ or _Reu barbarum_ occur in
the writings of Alexander Trallianus[1811] about the middle of the 6th
century, and in those of Benedictus Crispus,[1812] archbishop of Milan,
and Isidore[1813] of Seville, who both flourished in the 7th century.
Among the Arabian writers on medicine, the younger Mesue, in the early
part of the 11th century, mentions the rhubarb of China as superior to
the _Barbaric_ or Turkish.[1814] Constantinus Africanus[1815] about the
same period speaks of Indian and Pontic _Rheum_, the former of which he
declares to be preferable. In 1154 the celebrated Arabian geographer
Edrisi[1816] mentions rhubarb as a product of China, growing in the
mountains of Buthink—probably the environs of north-eastern Tibet near
Lake Tengri Nor (or Bathang in Western Szechuen?).
[1802] For further particulars see Flückiger, _Pharm. J._ vi. (1876)
861; also _Proc. Americ. Pharm. Assoc._ 1876. 130, with fig. showing
Rheum officinale grown in a poor soil.
[1803] Bretschneider, _Chinese Botanical Works_, Foochow, 1870. 2.
[1804] Flückiger, _l.c._
[1805] _Scriptores Historiæ Romanæ latini veteres_, ii. (1743) 511
(Amm. Marc. xxii. c. 8.)
[1806] _De Compositione Medicamentorum_, c. 167.
[1807] _De Medicinâ_. lib. v. c. 23.
[1808] Vincent, _Commerce and Navigation of the Ancients_, ii. (1807)
389.
[1809] _Ibid._, _op. cit._ ii. 390.
[1810] _Ibid._, _op. cit._ ii. 686.
[1811] Lib. viii. c. 3 (Haller’s edition).
[1812] Migne, _Patrologiæ Cursus_, lxxxix. 374.
[1813] Migne. _op. cit._, lxxxii. 628. The explanation given by Isidore
is this:—“_Reubarbarum_, sive _Reuponticum_: illud quod trans Danubium
in solo barbarico; istud quod circa Pontum colligitur, nominatum est.
_Reu_ autem _radix_ dicitur. _Reubarbarum_ ergo, quasi _radix barbara_.
_Reuponticum_ quasi _radix pontica_.” But Isidore was fond of such
derivations.
[1814] _Ravedsceni_, _Raved barbarum_, and _Raved Turchicum_ are the
terms used in the Latin translations we have consulted.
[1815] _De omnibus medico cognitu necessariis_, Basil. 1539. 354.
[1816] Translation of Jaubert, i. (Paris, 1836) 494.
Rhubarb in the 12th century was probably imported from India, as we
may infer from the tariff of duties levied at the port of Acon in
Syria, in which document[1817] it is enumerated along with many Indian
drugs. A similar list of A.D. 1271, relating to Barcelona, mentions
_Ruibarbo_.[1818] In a statute of the city of Pisa called the _Breve
Fundacariorum_, dating 1305, rhubarb (_ribarbari_) is classified with
commodities of the Levant and India.[1819]
The first and almost the only European who has visited the
rhubarb-yielding countries of China is the famous Venetian traveller,
Marco Polo,[1820] who speaking of the province of Tangut says—“ ... et
par toutes les montagnes de ces provinces se treuve le _reobarbe_ en
grant habondance. Et illec l’achatent les marchans et le portent par le
monde.”
A sketch of the history of rhubarb would be incomplete without some
reference to the various routes by which the drug has been conveyed
to Europe from the western provinces of the Chinese Empire, and which
have given rise to the familiar designations of _Russian_, _Turkey_ and
_China Rhubarb_.[1821]
[1817] _Assises de Jérusalem_ contained in the _Recueil des Historiens
des Croisades_, _Lois_, ii. (1843) 176.
[1818] Capmany, _Memorias de ... Barcelona_, i. (1779) 44.
[1819] Bonaini, _Statuti inediti della città di Pisa dal xii al xiv
secolo_, iii. (Firenze, 1857) 106. 115.
[1820] Pauthier, _Le Livre de Marco Polo ... rédigé en français sous sa
dictée en 1298 par Rusticien de Pise_, i. (1865) 165. ii. 490.
[1821] For further particulars, see my paper mentioned at page 493,
note 1.—F. A. F.
The _first_ route is that over the barren steppes of Central Asia by
Yarkand, Kashgar, Turkestan, and the Caspian to Russia; the _second_
by the Indus or the Persian Gulf to the Red Sea and Alexandria, or by
Persia to Syria and Asia Minor; and the _third_ by way of Canton, the
only port of the Chinese Empire which, previous to the year 1842, held
direct communication with Europe.
In 1653 China first permitted Russia to trade on her actual frontiers.
The traffic in Chinese goods was thereupon diverted from the line of
the Caspian and Black Sea further north, taking its way from Tangut
across the steppes of the high Gobi, and through Siberia by Tobolsk to
Moscow. Thus it is mentioned in 1719 that Urga on the north edge of
the Gobi desert was the principal depôt for rhubarb. From the earliest
times, Bucharian merchants appear to have been agents on this traffic,
the producers of the drug never concerning themselves about its export.
Consequent on the rectification of frontier in 1728, a line of
custom-houses was established by treaty between Russia and China,
whereby the commerce, previously unrestricted, was limited to the
government caravans which passed the frontier only at Kiachta and at
Zuruchaitu, south of Nerchinsk. The latter place always remained
unimportant, while Kiachta and the opposite Chinese town of Maimatchin
became the staple depôts of rhubarb.
The root was subjected to special control as early as 1687-1697 by
the Russian Government, who finally monopolized the trade about 1704.
Caravans fitted out by the Crown alone brought the drug to Moscow,
until 1762, when the caravan-trade was for a while thrown open. It was
not until this period that the export of rhubarb became considerable,
although the stringent regulations, established in 1736, were still
maintained. The surveillance of rhubarb was exercised at Kiachta in a
special court or office called the _Brake_,[1822] under instructions
from the Russian Minister of War, by an apothecary appointed for
six years, the object being to remove from the rhubarb brought for
inspection all inferior or spurious pieces, and to improve the selected
drug by trimming, paring and boring. It was then carefully dried, and
packed in chests, which were sown up in linen, and rendered impervious
to wet by being pitched and then covered with hide. The drug was
dispatched, but only in quantities of 1000 _puds_ (40,000 lb.), once
a year by way of Lake Baikal and Irkutsk to Moscow, whence it was
transmitted to St. Petersburg, to be there delivered to the Crown
apothecaries and in part to be sold to druggists.
We are indebted for these accounts chiefly to Calau,[1823] an
apothecary appointed to supervise the examination of rhubarb, and who
resided a long time at Kiachta. An exact account of the remarkable
policy of the Russian Government in relation to that drug was also
given by Von Schröders[1824] in 1864.
So long as China kept all her ports closed to foreign commerce except
Canton in the extreme south, a large supply of fine rhubarb found its
way to Europe by way of Russia. But the unpleasant accompaniments
of the Russian supervision, which was exercised with unsparing
severity,[1825] and the extreme tediousness of the land-transport, made
the Chinese very ready to accept an easier outlet for their goods.
Accordingly we find that the opening of a number of ports in the north
of China exerted a very depressing influence on the trade of Kiachta,
which was augmented by the rebellion that raged in the interior of
China for some years from 1852.
On these accounts Russia in 1855 removed certain restrictions on the
trade, though without abandoning the Rhubarb Office. She withdrew in
1860 the custom-house to Irkutsk, and declared Kiachta a free port,
while by the treaty with China of November 1860, she insisted on that
country abandoning all restrictions on trade.
But the overland rhubarb trade had already been destroyed: the Chinese,
tempted by the increased demand occasioned by the new trading-ports,
became less careful in the collection and curing of the root, while the
Russians insisted with the greatest strictness on the drug being of the
accustomed quality. Hence it happened that from 1860 hardly any rhubarb
was delivered at Kiachta, either for the government use or to private
traders; and in 1863 the Rhubarb Office was abolished.
[1822] From the German word _Bracke_, the name applied to persons
appointed for the examination of merchandize brought to the ports of
the Baltic.
[1823] Gauger’s _Rep. für Pharm. und Chemie_, 1842. 452-457; _Pharm.
Journ._ ii. (1843) 658.
[1824] Canstatt’s _Jahresbericht_ for 1864. i. 35-42.
[1825] Thus in 1860 the Russians compelled the Chinese to burn 6000 lb.
of rhubarb, on the pretext that it was _too small_!
Thus the so-called _Russian_ or _Muscovitic_ or _Crown Rhubarb_,
familiarly known in England as _Turkey Rhubarb_, a drug which for its
uniformly good quality long enjoyed the highest reputation, has become
a thing of the past, which can only now be found in museum collections.
It began to appear in English commerce at the commencement of the last
century. Alston,[1826] who lectured on botany and materia medica at
Edinburgh in 1720, speaks of rhubarb as brought from Turkey and the
East Indies,—“and of late, likewise from Muscovy.”
It has been shown (p. 494) that rhubarb was shipped from Syria in
the 12th century. Vasco da Gama[1827] mentions it in 1497 among the
exports of Alexandria. In fact, the drug was carried from the far
east to Persia, whence it was brought by caravans to Aleppo, Tripoli,
Alexandria, and even to Smyrna. From these Levant ports it reached
Europe, and was distributed as _Turkey Rhubarb_; while that which was
shipped direct from China, or by way of India, became known as _China_,
_Canton_, or _East India Rhubarb_. The latter was already the more
common sort in England as early as 1640.[1828]
As the rhubarb of the Levant disappeared from trade, that of Russia
took not only its place but likewise its name, until the term “_Turkey
Rhubarb_” came to be the accepted designation of the drug imported from
Russia. This strange confusion of terms was not however prevalent on
the Continent, but was chiefly limited to British trade.
The risk and expense of the enormous land-transport over almost the
whole breadth of Asia, caused rhubarb in ancient times to be one of the
very costly drugs. Thus at Alexandria in 1497, it was valued at twelve
times the price of benzoin. In France in 1542,[1829] it was worth
ten times as much as cinnamon, or more than four times the price of
saffron. At Ulm in 1596,[1830] it was more costly than opium. A German
price-list of the magistrate of Schweinfurt, of 1614, shows _Radix Rha
Barbari_ to be six times as dear as fine myrrh, and more than twice
the price of opium. An official English list[1831] giving the price
of drugs in 1657, quotes opium as 6_s._ per lb., scammony 12_s._, and
rhubarb 16_s._
=Production and Commerce=—The districts of the Chinese Empire which
produce rhubarb extend over a vast area. They are comprised in the
four northern provinces of China Proper, known as Chihli, Shansi,
Shensi,[1832] and Honan; the immense north-western province of
Kansuh, formerly partly included in Shensi, but now extending across
the desert of Gobi and to the frontiers of Tibet; the province of
Tsing-hai inhabited by Mongols, which includes the great salt lake of
Koko-nor and the districts of Tangut, Sifan, and Turfan; and lastly the
mountains of the western province of Szechuen. The plant is found on
the pasturages of the high plateaux, growing particularly well on spots
that have been enriched by encampments.
[1826] _Lectures on the Mat. Med._ i. (1770) 502.
[1827] _Roteiro da viagem de Vasco da Gama_, por A. Herculano e o Barão
de Castello de Paiva, ed. 2. Lisboa, 1861. 115.—For an abstract of the
“Roteiro,” see Flückiger, _Documente zur Geschichte der Pharm._ 1876.
13.
[1828] Parkinson, _Theatrum Botanicum_, 1640. 155.
[1829] Leber, _Appréciation de la fortune privée au moyen âge_, éd. 2.
1847. 308-9.
[1830] Reichard, _Beiträge zur Geschichte der Apotheken_, Ulm, 1825.
208.
[1831] _Book of the Values of Merchandize imported, according to which
Excize is to be paid by the First Buyer_, Lond. 1657.
[1832] According to Consul Hughes of Hankow, San-yuan in Shensi (north
of Sin-ganfu) is one of the principal marts for rhubarb.
What little we know regarding the production of rhubarb and its
preparation for the market, from Catholic missionaries,[1833] is of a
rather meagre and unsatisfactory character. The root is dug up at the
beginning of autumn when the vegetation of the plant is on the decline,
and the operation is probably continued for a few months, or in some
districts for the whole winter. It is cleaned, its cortical part sliced
off, and the root cut into pieces for drying. This is performed either
by the aid of fire-heat, or by simple exposure to sun and air, or the
pieces are first partially dried on a hot stone, and then strung on a
cord and suspended until the desiccation is complete.
According to F. von Richthofen[1834] the best rhubarb is collected
exclusively from plants growing wild in the high alps of western
Szechuen, especially in the Bayankara range, between the sources of the
Hoang-ho and the rivers Ya-lung-Kiang and Min-Kiang. This variety is
chiefly known under the name Shensi rhubarb, although the inhabitants
of the province of Szechuen pretend the superiority of the drug of
their own country. The important places for the commodity are Sining-fu
in the province of Kansu, and Kwan-hien in Szechuen. In the plain of
Tshing-tu-fu, according to Richthofen, rhubarb is cultivated in fields,
but its product is stated to be much inferior to that of the true plant
which is said not to succeed under culture.
Rhubarb is now purchased for the European market chiefly at Hankow on
the upper Yangtsze, whither it is brought from the provinces of Shensi,
Kansu, and Szechuen. From Hankow it is sent down to Shanghai, and there
shipped for Europe. The exports from Hankow are stated in official
documents[1835] to have amounted to the following numbers of peculs
(one pecul = 133⅓ lb. = 60·479 kilogrammes):
1866 1867 1868 1869 1870 1871 1872
2985 3425 2866 3398 3370 3859 3167
In 1877 there were exported by way of Hankow 2096 peculs from Shensi
and 3385 peculs from Szechuen.—From all the Chinese ports, 5124 peculs
of rhubarb were shipped in 1874.
Much smaller quantities (554 peculs in 1872, 1055 peculs in 1874) are
shipped from Tientsin; and there are occasional exportations from
Canton, Amoy, Foochow, and Ningpo. The imports of rhubarb into the
United Kingdom in 1870 amounted to 343,306 lb., the estimated value of
which was £62,716.[1836]
We have no information about the rhubarb which is stated by
Bellew[1837] to grow on the hills near Kayn or Ghayn in eastern Persia
(about 32½° N. lat.).
[1833] Chauveau, Vicar Apostolic of Tibet (1870), and Biet, a French
missionary, both quoted by Collin in his thesis _Des Rhubarbes_, Paris,
1871. 22. 24.
[1834] _Petermann’s Geograph. Mittheilungen_, viii. (1873) 302.
[1835] _Reports on Trade at the Treaty Ports of China for 1870_;
_Commercial Reports_ from Her Majesty’s Consuls in China, 1872. No. 3.
p. 57, and 1874 (1875) No. 5.
[1836] _Annual Statement of the Trade and Navigation of the United
Kingdom for 1870._ 79.
[1837] _From the Indus to the Tigris_, London, 1874. 321.
=Description=—China Rhubarb as imported into Europe[1838] consists
of portions of a massive root which display considerable diversity
of form, arising from the various operations of paring, slicing and
trimming, to which they have been subjected. Thus some pieces are
cylindrical or rather barrel-shaped, others conical, while a large
proportion are plano-convex, and others again are of no regular shape.
These forms are not all found in the same package, the drug being
usually sorted into _round_ and _flat rhubarb_. In dimensions we find 3
to 4 inches the commonest length, though an occasional piece 6 inches
long or more may be met with. The width may be stated at 2 to 3 inches.
The outer surface of the root is somewhat shrivelled, often exhibiting
portions of a dark bark that have not been pared away. Many pieces are
pierced with a hole, in which may be found the remains of a cord used
to suspend the root while drying. The drug is dusted over with a bright
brownish-yellow powder, on removal of which the outer side of the root
is seen to have a rusty-brown hue, or viewed with a lens to be marked
by the medullary rays, which appear as an infinity of short broken
lines of deep brown, traversing a white ground.
The character which most readily distinguishes the rhubarb of China is
that well-developed pieces, broken transversely, display these dark
lines arranged as an internal ring of _star-like spots_. Although this
character is by no means obvious in every piece of Chinese rhubarb, it
is of some utility from the fact that in European rhubarb, such spots
are generally wholly wanting, or at most occur only sparingly and in an
isolated manner.
In judging of rhubarb, great stress is laid upon the appearance of
the root when broken, and the circumstance of the fractured surface
presenting no symptoms of decay, discoloration, or sponginess.[1839]
In good rhubarb, the interior is found to be compact, and beautifully
veined with reddish-brown and white, sometimes not unmixed with
iron-grey. The root when chewed tastes gritty, by reason of the
crystals it contains of oxalate of calcium; but it is besides bitter,
astringent and nauseous. The odour is peculiar, and except by the
druggist, is mostly regarded as very disagreeable.
_Microscopic Structure_—The tissue of rhubarb is made up of a white
parenchyme, brown medullary rays and a few irregularly scattered very
large fibro-vascular bundles, which are devoid of ligneous cells.
On a transverse fracture of specimens, which are not too much peeled,
a narrow dark cambial zone may be distinguished. In that part of the
root, only the medullary rays display the usual radial arrangement, and
in the interior of the root no regular structure is met with. There
is no well-marked pith, but the central portion of the tissue shows a
mixture of white parenchyme and brown medullary rays running in every
direction. In full-grown roots, the central part is separated from the
cambial zone by the band of stellate patches[1840] already mentioned.
[1838] It is now often trimmed by wholesale druggists to simulate the
old Russian rhubarb.
[1839] The quality and appearance of rhubarb are far more regarded in
England than on the Continent. To ensure a fine powder of brilliant
hue, the drug is most carefully prepared, each root being split open,
and any dark or decayed portion removed with a chisel or file, while
the operator is not allowed to handle the drug except with leather
gloves.
[1840] Their formation has been investigated by Schmitz, Proceedings of
the “_Naturforschende Gesellschaft zu Halle_”; the author also shows
that the drug is chiefly afforded by the rhizome.—An abstract of the
paper will be found in Just’s _Botanischer Jahresbericht_, 1874. 461.
As to the contents of the white cells, they are loaded either with
starch or tufted crystals of oxalate of calcium, the amount of the
latter being especially liable to variation. Scheele, after having
discovered the oxalic acid, pointed out in 1784 that the crystals under
notice consist of that acid in combination with lime; he was the first
to point out the true composition of those crystals which are of so
wide a distribution throughout the vegetable kingdom. The medullary
rays contain the substances peculiar to rhubarb, but none of them occur
in a crystalline state.
=Chemical Composition=—The active constituent of the root has long
been supposed to reside in the yellowish-red contents of the medullary
rays. Schrader as early as 1807 prepared a _Rhubarb-Bitter_, to which
he attributed the medicinal powers of the drug. Since then several
substances of the same kind have been separated by various methods,
and described under different names: such are the _Rhabarberstoff_ of
Trommsdorff, the _Rheumin_ of Hornemann, the _Rhabarberin_ of Buchner
and Herberger, the _Rhubarb-Yellow_ or _Rheïn_, and the _Rhabarbaric
Acid_ of Brandes.
Schlossberger and Döpping in 1844 first recognized among the
above-named substances a definite chemical body named _Chrysophan_ or
_Chrysophanic Acid_,
{CH₃ }
C₁₄H₅ { }O₂,
{(OH)₂}
which had been found in 1843 by Rochleder and Heldt in the yellow
lichen, _Parmelia parietina_. It partly forms the yellow contents of
the medullary rays of rhubarb, and when isolated crystallizes in golden
yellow needles or in plates. It dissolves in ether, alcohol, or benzol;
though scarcely soluble in water, it is nevertheless extracted from
the root to some extent by that solvent, probably by reason of some
accompanying substance. Alkalis dissolve it, forming fine dark red
solutions. Chrysophan, C₁₅H₁₀O₄, is a derivative of anthracene, C₁₄H₁₀,
and closely allied to alizarin, C₁₄H₈O₄.
By precipitating alcoholic solutions of extract of rhubarb with ether,
Schlossberger and Döpping obtained, together with chrysophan, resinous
bodies which they named _Aporetin_, _Phæoretin_ and _Erythroretin_.
De la Rue and Müller (1857) extracted from rhubarb, in addition to
chrysophan, an allied substance, _Emodin_, which crystallizes in
orange-coloured prisms, sometimes as much as two inches long. Its
constitution was subsequently found to agree with the formula
{CH₃ }
C₁₄H₄ { }O₂.
{(OH)₃}