_Aloes_; F. _Aloès ou Suc d’Aloès_; G. _Aloë_.
=Botanical Origin=—Several species of _Aloë_[2539] furnish a bitter
juice which when inspissated forms this drug. These plants are natives
of arid, sunny places in Southern and Eastern Africa, whence a few
species have been introduced into Northern Africa, Spain,[2540] and the
East and West Indies.
The aloes are succulent plants of liliaceous habit with persistent
fleshy leaves, usually prickly at the margin, and erect spikes of
yellow or red flowers. Many are stemless; others produce stems some
feet in height, which are woody and branching. In the remote districts
of Namaqua Land and Damara Land in Western South Africa, and in the
Transkei Territory and Northern Natal to the eastern, aloes have been
discovered which attain 30 to 60 feet in height, with stems as much as
12 feet in circumference.[2541] The following species may be named with
more or less of certainty as yielding the drug.[2542]
_Aloë socotrina_ Lam. (_A. vera_ Miller), native of the southern shores
of the Red Sea and Indian Ocean, Socotra, and Zanzibar (?). It is the
source of the _Socotrine_ and _Moka Aloes_. _A. officinalis_ Forsk. and
_A. rubescens_ DC. are considered to be varieties of this plant. _A.
abyssinica_ Lam. may probably contribute to the aloes shipped from the
Red Sea.
_A. vulgaris_ Lam. _A. perfoliata_, var. π. _vera_ Linn., _A.
barbadensis_ Mill., a plant of India and of Eastern and Northern
Africa, now found also on the shores of Southern Spain, Sicily, Greece,
and the Canaries; introduced in the beginning of the 16th century (or
earlier) into the West Indies. It affords _Barbados_ and _Curaçao
Aloes_. _A. indica_ Royle, a plant of the North-west Provinces of
India, common in Indian gardens, appears to be a slight variety of
_A. vulgaris_ Lam. _A. litoralis_ König, said to grow in abundance
at Cape Comorin, is unknown to us. Dr. Bidie suggests that it is a
form of the preceding, stunted by a poor saline soil and exposure to
the sea breeze. Both _A. indica_ and _A. litoralis_ are named in the
_Pharmacopœia of India_.
_Aloë ferox_ L., and hybrids obtained by crossing it with _A. africana_
Mill. and _A. spicata_ Thunberg, _A. perfoliata_ Linn. (_quoad_ Roxb.)
and _A. linguæformis_ are reputed to yield the best _Cape Aloes_.
_A. africana_ Mill. and its varieties, and _A. plicatilis_ Mill. afford
an extract which Pappe[2543] says is thought to be less powerful.
[2539] From the Syriac _Alwai_.
[2540] _Aloë arborescens_, _A. purpurascens_, and _A. vulgaris_ may be
seen luxuriantly growing in Valencia, Granada, Gibraltar.
[2541] Dyer in _Gardeners’ Chronicle_, May 2, 1874, with figures.
[2542] Good figures of _Aloë africana_, _A. arborescens_, _A. ferox_,
_A. purpurascens_, _A. socotrina_, and _A. vulgaris_ will be found in
the work _Monographia generis Aloës et Mesembryanthemi_, auctore Jos.
Principe de Salm-Reifferscheid-Dyck, Bonnae, 1836-1863. fol.
[2543] _Floræ Capensis Medicæ Prodromus_, ed. 2, 1857. 41.
_A. arborescens_ Mill., _A. Commelini_ Willd. and _A. purpurascens_
Haworth are stated to produce a portion of the _Cape Aloes_ of
commerce.[2544]
Various species of _Agave_, especially _A. americana_ L., are largely
grown, since the first half of the 16th century, in the south of
Europe, and popularly called _Aloë_. All of them are plants of Mexico,
while the true aloes are natives of the old world. Botanically the
genus _Agave_ differs from _Aloë_, in that the former has the ovary
_inferior_, while in the latter it is _superior_. From a chemical point
of view there is also no analogy at all between Aloë and Agave.
=History=—Aloes was known to the Greeks as a production of the island
of Socotra as early as the 4th century B.C., if we might credit a
remarkable legend thus given in the writings of the Arabian geographer
Edrisi.[2545] When Alexander had conquered the king of the Persians
and his fleets had vanquished the islands of India, and he had killed
Pour, king of the Indies, his master Aristotle recommended him to
seek the island that produces _Aloes_. So when he had finished his
conquests in India, he returned by way of the Indian Sea into that of
Oman, conquered the isles therein, and arrived at last at Socotra,
of which he admired the fertility and the climate. And from the
advice which Aristotle gave him he determined to remove the original
inhabitants and to put Greeks in their place, enjoining the latter to
preserve carefully the plant yielding aloes, on account of its utility,
and because that without it certain sovereign remedies could not be
compounded. He thought also that the trade in and use of this noble
drug would be a great advantage for all people. So he took away the
original people of the island of Socotra, and established in their
stead a colony of Ionians, who remained under his protection and that
of his successors, and acquired great riches, until the period when the
religion of the Messiah appeared, which religion they embraced. They
then became Christians, and so their descendants have remained up to
the present time (_circa_ A.D. 1154).
This curious account, which Yule[2546] says is doubtless a fable,
but invented to account for facts, is alluded to by the Mahomedan
travellers of the 9th century[2547] and in the 10th by Masudi,[2548]
who says that in his time aloes was produced only in the island of
Socotra, where its manufacture had been _improved_ by Greeks sent
thither by Alexander the Great.
Aloes is not mentioned by Theophrastus, but appears to have been well
known to Celsus, Dioscorides, Pliny and the author of the Periplus of
the Erythrean Sea, as well as to the later Greek[2549] and the Arabian
physicians. From the notices of it in the Anglo-Saxon leech-books and a
reference to it as one of the drugs recommended to Alfred the Great by
the Patriarch of Jerusalem, we may infer that its use was not unknown
in Britain as early as the 10th century.[2550]
[2544] In the above revision of the medicinal species of _Aloë_ we
have made free use of the observations on the same subject mentioned
in the _Dictionnaire de Botanique_. We have also had the advantage of
consulting W. Wilson Saunders, Esq., F.R.S., whose long familiarity
with these plants in cultivation impart great weight to his opinion.
[2545] _Géographie d’Edrisi_, i. (1836) 47.
[2546] _Marco Polo_, ii. 343.
[2547] _Anciennes Relations des Indes et de la Chine de deux Voyageurs
Mahométans, qui y allèrent dans le neuvième siècle_, traduites de
l’Arabe, Paris, 1718. 113.
[2548] Tome iii. 36.—See Appendix.
[2549] Alexander Trallianus, in Puschmann’s edition (quoted in the
Appendix), i. 578, speaks of Αλόης ὴπατίτιὸυς—_Aloë hepatica_.
[2550] See p. 439. note 1.
At this period and for long afterwards the drug was imported into
Europe by way of the Red Sea and Alexandria. After the discovery of
a route to India by the Cape of Good Hope the old line of commerce
probably began to change.
Pires, an apothecary at Cochin, in a letter on Eastern drugs[2551]
addressed to Manuel, king of Portugal, in 1516, reports that aloes
grows in the island of Çacotora, Aden, Cambaya, Valencia of Arragon,
and in other parts,—the most esteemed being that of Çacotora, and next
is that of Spain; while the drug of Aden and Cambaya is so bad as to be
worthless.
In the early part of the 17th century there was a direct trade in aloes
between England and Socotra; and in the records of the East India
Company there are many notices of the drug being bought of the “King of
Socotra.” Frequently the king’s whole stock of aloes is mentioned as
having been purchased.[2552]
Wellstead, who travelled in Socotra in 1833,[2553] says that in old
times the aloë was far more largely grown there than at present, and
that the walls which enclosed the plantations may still be seen. He
adds that the produce was a monopoly of the Sultan of the island. At
the present day the few productions of Socotra that are exported are
carried by the Arab coasting vessels, coming annually from the Persian
Gulf to Zanzibar, at which place they are transshipped for Indian and
other ports. Dr. Kirk, who has resided at Zanzibar from 1866 to 1873,
informs us that aloes from Socotra arrives in a very soft state packed
in goatskins. From these it is transferred to wooden boxes, in which
it concretes, and is shipped to Europe and America. To avoid loss the
skins have to be washed; and the aloetic liquor evaporated.
Ligon,[2554] who visited the island of Barbados in 1647-50, that is
about twenty years after the arrival of the first settlers, speaks of
the aloë as if it were indigenous, mentioning also the useful plants
which had been introduced. At that period the settlers knew how to
prepare the juice for medicinal use, but had not begun to export it.
Barbados aloes was in the drug warehouses of London in 1693.[2555]
The manufacture of aloes in the Cape Colony of South Africa was
observed by Thunberg in 1773 on the farm of a boer named Peter de Wett,
who was the first to prepare the drug in that country.[2556] Cape Aloes
is enumerated in the stock of a London druggist in 1780, its cost being
set down as £10 per cwt. (1_s._ 9½_d._ per lb.).
A new and distinct sort of aloes, manufactured in the colony of Natal,
appeared in English commerce in 1870. It will be described further on.
_Lignum Aloes_—It is important to bear in mind that the word _Aloes_
or _Lign Aloës_, in Latin _Lignum Aloës_, is used in the Bible and in
many ancient writings to designate a substance totally distinct from
the modern _Aloes_, namely the resinous wood of _Aquilaria Agallocha_
Roxburgh, a large tree[2557] of the order Thymeleaceæ, growing in the
Malayan Peninsula. Its wood constituted a drug[2558] which was, down
to the beginning of the present century, generally valued for use as
incense, but now esteemed only in the East.
[2551] See Appendix.
[2552] _Calendar of State Papers_, Colonial Series, East Indies, China
and Japan, 1513-1616, Lond. 1862.
[2553] _Journ. of the Roy. Geograph. Soc._ v. (1835) 129-229.
[2554] _History of Barbadoes_, Lond. 1673. 98.
[2555] Dale’s _Pharmacologia_ (1693) 361.
[2556] Thunberg, _Travels in Asia, Europe and Africa_, ii. 49. 50.
[2557] Fig. in Royle, _Illustr. of the Himalayan Bot. etc._ (1839) tab.
36. See also _Dictionnaire de Botanique_.
[2558] Hanbury, _Science Papers_, 1876. 263; also Flückiger, _Die
Frankfurter Liste_, Halle, 1873. 37. (_Archiv der Pharm._ cci.
511).—For full historical information see Heyd, _Levantehandel_, ii.
(1879), 559.
=Structure of the Leaf=—The stout fleshy leaves of an aloë have a
strong cuticle and thick-walled epidermis. Their interior substance
is formed of very loose, large-celled, colourless pulp, traversed
by vascular bundles, which, on transverse section, are seen to be
accompanied by a group of large thin-walled cells[2559] containing the
bitter juice which constitutes the drug under notice. These cells, on a
longitudinal section, are seen to be considerably elongated, adjoining
a single row of smaller, prismatic, truncated cells,[2560] by which
the former are separated from the cortical layer. The prismatic cells
contain a yellow juice, apparently different from that which yields
aloes. The cortical tissue is filled with granules of chlorophyll,
and exhibits between the cells groups of needles of calcium oxalate.
Similar crystals are also found sparingly in the pulp.
The transparent pulp-tissue[2561] is rich in mucilage, which after
dilution with water is precipitated by neutral acetate of lead, but is
not coagulated by boiling.
The amount of bitter principles in the leaf probably varies with the
age of the latter and with the season of the year. Haaxman mentions
that, in Curaçao, the maximum is found when the leaves are changing
from green to brown.
=Cultivation and Manufacture=—In Barbados,[2562] where _Aloë vulgaris_
is systematically cultivated for the production of the drug, the
plants are set 6 inches apart, in rows which are 1 to 1½ foot asunder,
the ground having been carefully prepared and manured. They are kept
free from grass and weeds, but yams or pulse are frequently grown
between them. The plants are always dwarf, never in the least degree
arborescent; almost all of those above a year old bear flowers, which
being bright yellow, have a beautiful effect. The leaves are 1-2 feet
long; they are cut annually, but this does not destroy the plant,
which, under good cultivation, lasts for several years.
[2559] The cells lettered _e_ in Berg’s figure C, plate iv. _f._ of his
“_Offizinelle Gewächse_.”
[2560] The cells _d_, in Berg’s figure.
[2561] This central pulpy tissue is _quite tasteless_, and is actually
used as food in times of scarcity in some parts of India.—Stewart,
_Punjab Plants_, 1869. 232.
[2562] For the particulars we here give respecting Barbados aloes,
we have cordially to thank Sir R. Bowcher Clarke, Chief Justice of
Barbados, and also Major-General Munro, stationed (1874) at Barbados in
command of troops.
The cutting takes place in March and April, and is performed in the
heat of the day. The leaves are cut off close to the plant, and placed
_very quickly_, the cut end downwards, in a V-shaped wooden trough,
about 4 feet long and 12 to 18 inches deep. This is set on a sharp
incline, so that the juice which trickles from the leaves very rapidly
flows down its sides, and finally escapes by a hole at its lower end
into a vessel placed beneath. No pressure of any sort is applied to
the leaves. It takes about a quarter of an hour to cut leaves enough
to fill a trough. The troughs are so distributed as to be easily
accessible to the cutters. Their number is generally five; and by the
time the fifth is filled, the cutters return to the first and throw
out the leaves, which they regard as exhausted. The leaves are neither
infused nor boiled, nor is any use afterwards made of them except for
manure.
When the vessels receiving the juice become filled, the latter is
removed to a cask and reserved for evaporation. This may be done at
once, or it may be delayed for weeks or even months, the juice, it
is said, not fermenting or spoiling. The evaporation is generally
conducted in a copper vessel; at the bottom of this is a large ladle,
into which the impurities sink, and are from time to time removed
as the boiling goes on. As soon as the inspissation has reached the
proper point, which is determined solely by the experienced eye of the
workman, the thickened juice is poured into large gourds or into boxes,
and allowed to harden.
The drug is not always readily saleable in the island, but is usually
bought up by speculators who keep it till there is a demand for it in
England. The cultivators are small proprietors, but little capable as
to mind or means of making experiments to improve the manufacture of
the drug. It is said, however, that occasionally a little aloes of very
superior kind is made for some special purpose by exposing the juice
in a shallow vessel to solar heat till completely dry. But such a drug
is stated to cost too much time and trouble to be profitable.[2563]
The manufacture of aloes in the Dutch West Indian island of Curaçao is
conducted in the same manner.[2564]
The manufacture of aloes in the Cape Colony has been thus described to
us in a letter[2565] from Mr. Peter MacOwan of Gill College, Somerset
East:—The operator scratches a shallow dish-shaped hollow in the dry
ground, spreads therein a goatskin, and then proceeds to arrange around
the margin a radial series of aloë leaves, the cut ends projecting
inwards. Upon this, a second series is piled, and then a third—care
being taken that the ends of each series overhang sufficiently, to drop
clear into the central hollow. When these preparations have been made,
the operator either “loafs about” after wild honey, or, more likely,
lies down to sleep. The skin being nearly filled, four skewers run in
and out at the edge square-fashion, give the means of lifting this
primitive saucer from the ground, and emptying its contents into a
cast-iron pot. The liquid is then boiled, an operation conducted with
the utmost carelessness. Fresh juice is added to that which has nearly
acquired the finished consistence; the fire is slackened or urged just
as it happens, and the boiling is often interrupted for many hours,
if neglect be more convenient than attention. In fact, the process is
thoroughly barbarous, conducted without industry or reflection; it is
mostly carried on by Bastaards and Hottentots, but not by Kaffirs.
“The only aloë I have seen used,” says Mr. MacOwan, “is the very large
one with di-or tri-chotomous inflorescence,—_A. ferox_, I believe.”
Backhouse[2566] also names “_Aloë ferox?_” as the species he saw used
near Port Elizabeth in 1838.
[2563] Some extremely fine Barbados aloes in the London market in 1842
was said to have been manufactured in a vacuum-pan.
[2564] Oudemans, _Handleiding tot de Pharmacognosie_, 1865. 316.
[2565] Under date May 7, 1871, addressed to myself.—D. H.
[2566] _Visit to Mauritius and South Africa_, 1844. 157, also 121.
From another correspondent, we learn that the making of aloes in the
Cape Colony is not carried on by preference, but is resorted to when
more profitable work is scarce. The drug is sold by the farmers to
the merchants of the towns on the coast, some of whom have exerted
themselves to obtain a better commodity, and have even imported living
aloe-plants from Barbados.
Nothing is known of the manufacture of the so-called _Socotrine_ or
_Zanzibar Aloes_, or even with certainty in what precise localities it
is carried on.
=General Description=—The differences in the several kinds of
commercial aloes are due to various causes, such as the species of
_Aloë_ employed and the method of extracting the juice. The drug varies
exceedingly: some is perfectly transparent and amorphous, with a glassy
conchoidal fracture; some is opaque and dark with a dull waxy fracture,
or opaque and pallid; or it may be of a light orange-brown and highly
crystalline. It varies in consistence in every degree, from dry and
brittle to pasty, and even entirely fluid and syrup-like.
These diverse conditions are partially explained by an examination
of the very fluid aloes that has been imported of recent years from
Bombay. If some of this aloes is allowed to repose, it gradually
separates into two portions,—the upper a transparent, black liquid,—the
lower, an orange-brown crystalline sediment. If the whole be allowed to
evaporate spontaneously, we get aloes of two sorts in the same mass;
the one from the upper portion being dark, transparent and amorphous,
the other rather opaque and highly crystalline. Should the two layers
become mixed, an intermediate form of the drug results.
The _Hepatic Aloes_ of the old writers[2567] was doubtless this rather
opaque form of Socotrine Aloes; but the term has come to be used
somewhat vaguely for any sort of liver-coloured aloes, and appears to
us unworthy to be retained. Much of the opaque, so-called _Hepatic
Aloes_ does not however owe its opacity to crystals, but to a feculent
matter the nature of which is doubtful.
The odour of aloes is a character which is much depended on by dealers
for distinguishing the different varieties, but it can only be
appreciated by experience, and certainly cannot be described.[2568]
[2567] As Macer Floridus in the 10th century, who writes:—
“Sunt Aloës species geminæ, quæ subrubet estque Intus sicut hepar cum
frangitur, hæc _epatite_ Dicitur et magnas habet in medicamine vires,
Utilior piceo quæ fructa colore videtur.”
[2568] Thus the pale, liver-coloured aloes of Natal is invariably
associated with the transparent Cape Aloes, simply from the fact that
the two drugs have a similar smell. Again, the aloes of Curaçao is at
once recognized by its odour, which an experienced druggist pronounces
to be quite different from that of the aloes produced in Barbados.
=Varieties=—The principal varieties of aloes found in English commerce
are the following:—
1. _Socotrine Aloes_—also called _Bombay_, _East Indian_, or _Zanzibar
Aloes_, and when opaque and liver-coloured, Hepatic Aloes. It is
imported in kegs and tin-lined boxes from Bombay, whither it has
been carried by the Arab traders from the African coast, the Red Sea
ports, or by way of Zanzibar, from Socotra. When of fine quality, it
is of a dark reddish-brown, of a peculiar, rather agreeable odour,
comparable to myrrh or saffron. In thin fragments, it is seen to be
of an orange-brown; its powder is of a tawny reddish-brown. When
moistened with spirit of wine, and examined in a thin stratum under
the microscope, good Socotrine Aloes is seen to contain an abundance
of crystals. As imported, it is usually soft, at least in the interior
of the mass, but it speedily dries and hardens by keeping.[2569] It is
occasionally imported in a completely fluid state (_Liquid Socotrine
Aloes_, _Aloë Juice_), and is not unfrequently somewhat sour and
deteriorated.
Some fine aloes from Zanzibar, of which a very small quantity was
offered for sale in 1867, was contained in a skin, and composed of two
layers, the one amorphous, the other a granular translucent substance
of light colour, which when softened and examined with a lens, was seen
to be a mass of crystals. A very bad, dark, fœtid sort of aloes is
brought to Aden from the interior. It seems to be the _Moka Aloes_ of
some writers.
The quantity of aloes imported into Bombay in the year 1871-72 was 892
cwt., of which 736 cwt. are reported as shipped from the Red Sea ports
and Aden.[2570]
[2569] The average loss as estimated in the drying of 560 lb., upon
several occasions, was about 14 per cent.—Laboratory statistics,
communicated by Messrs. Allen and Hanburys, London.
[2570] _Statement of the Trade and Navigation of the Presidency of
Bombay for 1871-72_, pt. ii. 19.
2. _Barbados Aloes_—Characteristic samples show it as a hard dry
substance of a deep chocolate-brown, with a clean, dull, waxy fracture.
In small fragments it is seen to be translucent and of an orange-brown
hue. When breathed upon, it exhales an odour analogous to, but easily
distinguishable from, that of Socotrine aloes. It is imported in
boxes and gourds. The gourds, into which the aloes has been poured in
a melted state through a square hole, over which a bit of calico is
afterwards nailed, contain from 10 to 40 lb. or more. Of late years,
Barbados aloes having a smooth and glassy fracture has been imported;
it is known to the London drug-brokers as “_Capey Barbados_.” By
keeping, it passes into the usual variety having a dull fracture.
The export of aloes from Barbados in 1871, as shown by the _Blue Book_
for that colony, was 1046 cwt., of which 954 cwt. were shipped to the
United Kingdom.
3. _Curaçao Aloes_—manufactured in the Dutch West Indian islands of
Curaçao, Bonaire, and Aruba, is imported into this country by way
of Holland, packed in boxes of 15 to 28 lb. each. In appearance it
resembles Barbados aloes, but has a distinctive odour.
4. _Cape Aloes_—The special features of this sort of aloes are its
brilliant conchoidal fracture and peculiar odour. Small splinters seen
by transmitted light are highly transparent and of an amber colour;
the powder is of a pale tawny yellow. When the drug is moistened and
examined under the microscope, no crystals can be detected, even after
the lapse of some days. Cape aloes has the odour of other kinds of
aloes, with a certain sourish smell which easily distinguishes it.
Several qualities are recognized, chiefly by the greater or lesser
brilliancy of fracture, and by the tint of the powder.
From the _Blue Book_ for the Colony of the Cape of Good Hope, published
at Cape Town in 1873, it appears that the export of aloes in 1872 was
484,532 lb. (4326 cwt.); and that the average market value during the
year was 3¾_d._, the lowest price, 1½_d._, being at Riversdale and
Mossel Bay, and the highest, 11_d._, at Swellendam. The drug is shipped
from Cape Town, Mossel Bay and Algoa Bay.
5. _Natal Aloes_—Aloes is also imported from Natal, and since 1870 in
considerable quantity. Most of it is of an hepatic kind and completely
unlike the ordinary Cape aloes, inasmuch as it is of a greyish-brown
and very opaque. Moreover it contains a crystalline principle which has
been found in no other sort of aloes.
The drug is manufactured in the upper districts of Natal, between
Pietermaritzburg and the Quathlamba mountains, especially in the Umvoti
and Mooi River Counties, at an elevation of 2000 to 4000 feet above the
sea. The plant used is a large aloë which has not yet been botanically
identified. The people who make the drug are British and Dutch
settlers, employing Kaffir labourers. The process is not very different
from that followed in making Cape aloes, but is conducted with more
intelligence. The leaves are cut obliquely into slices, and allowed to
exude their juice in the hot sunshine. The juice is then boiled down in
iron pots, some care being taken to prevent burning, by stirring the
liquid as it becomes thick. The drug while still hot, is poured into
wooden cases, in which it is shipped to Europe.[2571] The exports from
the colony have been as follows:—[2572]
1868 1869 1870 1871 1872
none 38 cwt. 646 cwt. 372 cwt. 501 cwt.
=Chemical Composition=—All kinds of aloes have an odour of the same
character and a bitter disagreeable taste. The odour which is often not
unpleasant, especially in Socotrine aloes, is due to a _volatile oil_,
which the drug contains only in minute proportion. T. and H. Smith of
Edinburgh, who contributed a specimen of it to the Vienna Exhibition
of 1873, inform us that they obtained it by subjecting to distillation
with water 400 lb. of aloes, which quantity they estimate to have
yielded about an ounce. The oil is stated in a letter we have received
from them, to be a mobile pale yellow liquid, of sp. gr. 0·863, with a
boiling point of 266-271° C.
Pure aloes dissolves easily in spirit of wine with the exception of a
few flocculi; it is insoluble in chloroform and bisulphide of carbon,
as well as in the so-called petroleum ether, the most volatile portion
of American petroleum. The sp. gr. of fine transparent fragments of
aloes, dried at 100° C., and weighed in the last named fluid at 16° C.,
was found by one of us (F.) to be 1·364; showing that aloes is much
more ponderous than most of the resins, which seldom have a higher
sp. gr. than 1·00 to 1·10. In water aloes dissolves completely only
when heated. On cooling, the aqueous solution, whether concentrated
or dilute, becomes turbid by the separation of resinous drops, which
unite into a brown mass,—the so-called _Resin of Aloes_.[2573] The
clear solution, after separation of this substance, has a slightly
acid reaction; it is coloured dark brown by alkalis, black by ferric
chloride, and is precipitated yellowish-grey by neutral lead acetate.
Cold water dissolves about half its weight of aloes, forming an acid
liquid which exhibits similar reactions. The solution of aloes in
potash or ammonia is precipitated by acids, but not by water.
[2571] We have to thank J. W. Akerman, Esq., of Pietermaritzburg, for
the foregoing information as to the manufacture of this drug.
[2572] _Blue Books for the Colony of Natal for 1868, 1869, 1870, 1871,
1872._
[2573] The average yield of aqueous extract made by the pharmacopœia
process from commercial Socotrine aloes containing about 14 per cent.
of water, was found from the record of five experiments, in which 179
lb. were used, to be 62·7 per cent. Barbados aloes, which is always
much drier, afforded on an average 80 per cent.
The most interesting constituents of aloes are the substances known
as _Aloïn_. This name was originally applied to an aloïn which, as
it appears to be found exclusively in Barbados aloes, is now termed
_Barbaloïn_, in order to distinguish it from allied substances
occurring in Natal and Socotrine aloes.
Barbaloïn was discovered by T. and H. Smith of Edinburgh in 1851,[2574]
and was described (1851) by Stenhouse. From good qualities of the drug
it can be obtained, according to Tilden,[2575] as a crystalline mass,
to the extent of 20 to 25 per cent., but in others it appears to occur
partly amorphous or in a chemically altered state. Barbaloïn is a
neutral substance, crystallizing in tufts of small yellow prisms. These
crystals represent _hydrated_ aloïn, and part with one molecule of
water (=2·69 per cent.) by desiccation _in vacuo_, or by the prolonged
heat of a water-bath. Barbaloïn, C₃₄H₃₆O₁₄ + H₂O, dissolves sparingly
in water or alcohol but very freely if either liquid be even slightly
warmed; it is insoluble in ether.
The solutions alter quickly if made a little alkaline, but if neutral
or slightly acid, are by no means very prone to decomposition. By
oxidation with nitric acid, barbaloïn yields, as Tilden (1872) has
shown, about a third of its weight of chrysammic acid, besides aloëtic,
oxalic, and picric acids. It easily combines with bromine to form
yellow needles of _Bromaloïn_, C₃₄H₃₀Br₆O₁₄; _Chloraloïn_, C₃₄H₃₀Cl₆O₁₄
+ 6H₂O, crystallizing in prisms, has likewise been obtained.
In examining Natal aloes in 1871, we observed it to contain a distinct
crystalline body, much less soluble than the ordinary aloïn of Barbados
aloes. We have accordingly named it _Nataloïn_.
Nataloïn exists naturally in Natal aloes, from which it can be easily
prepared in the crude state, if the drug is triturated with an equal
weight of alcohol at a temperature not exceeding 48° C. This will
dissolve the amorphous portion, from which the crystals should be
separated by a filter, and washed with a small quantity of cold spirit.
From 16 to 25 per cent. of crude nataloïn in pale yellow crystals may
be thus extracted. When purified by crystallization from methylic
alcohol or spirit of wine, it forms thin, brittle, rectangular scales,
often with one or more of their angles truncated. The formula assigned
to nataloïn by Tilden, which is supported by the composition of the
acetyl derivative he has succeeded in obtaining, is C₂₅H₂₈O₁₁.
At 15·5° C., 60 parts of alcohol, 35 of methylic alcohol,[2576] 50 of
acetic ether, 1236 of ether, and 230 of absolute alcohol, dissolve
respectively one part of nataloïn. It is scarcely more soluble in
warm than in cold spirit of wine, so that to obtain crystals it is
best to allow the solution to evaporate spontaneously. Water hot or
cold dissolves it very sparingly. Nataloïn gives off no water when
exposed over oil of vitriol, or to a temperature of 100° C. By the
action of nitric acid, it affords both oxalic and picric acids, but no
chrysammic acid. It appears not to combine with chlorine or bromine,
and we have failed in obtaining from it any such body as bromaloïn.
[2574] Most beautiful specimens have been presented to each of us by
these gentlemen.
[2575] _Pharm. Journ._ April 28, 1872. 845.—See also Nov. 5, 1870. 375.
[2576] The best crystals can be got by this solvent.
Liquid Socotrine aloes, imported into London about 1852, was noticed
by Pereira to abound in minute crystals, which he termed the _Aloïn
of Socotrine Aloes_, and regarded as probably identical with that of
Barbados aloes. Some fine dry aloes from Zanzibar of very pale hue, in
our possession, is in reality a perfectly crystalline mass.
Histed was the first to assert that the crystalline matter of Socotrine
or Zanzibar aloes is a peculiar substance, according neither with
barbaloïn nor with nataloïn. This observation was fully corroborated
by our own experiments,[2577] made chiefly on the Zanzibar aloes just
described, and we shall call the substance thus discovered _Socaloïn_.
In this drug, the crystals are prisms of comparatively large size, such
as we have never observed in Natal aloes. They cannot be so easily
isolated as nataloïn, since they are nearly as soluble as the amorphous
matter surrounding them. Histed recommends treating the powdered crude
drug with a little alcohol, sp. gr. 0·960, and strongly pressing the
pasty mass between several thicknesses of calico; then dissolving
the yellow crystalline cake in warm weak alcohol, and collecting the
crystals which are formed by cooling and repose.
Socaloïn forms tufted acicular prisms, which by solution in methylic
alcohol may be got 2 to 3 millimetres long. It is much more soluble
than nataloïn. At ordinary temperatures, 30 parts of alcohol, 9 of
acetic ether, 380 of ether, 90 of water are capable of dissolving
respectively one part of socaloïn; while in methylic alcohol, it is
most abundantly soluble. Socaloïn is a hydrate, losing when dried over
oil of vitriol 11 to 12 per cent. of water, but slowly regaining it if
afterwards exposed to the air. Its elementary composition according to
the analysis made by one of us (F.) is C₃₄H₃₈O₁₅ + 5 H₂O. We have not
succeeded in obtaining any well-defined bromine compound of socaloïn.
The three aloïns, _Barbaloïn_, _Nataloïn_, and _Socaloïn_, are easily
distinguished by the following beautiful reaction first noticed by
Histed:—a drop of nitric acid on a porcelain slab gives with a few
particles of barbaloïn or nataloïn, a vivid crimson,[2578] but produces
little effect with socaloïn. To distinguish barbaloïn from nataloïn,
test each by adding a minute quantity to a drop or two of oil of
vitriol, then allowing the _vapour_ from a rod touched with nitric acid
to pass over the surface. Barbaloïn (and socaloïn) will undergo no
change, but nataloïn will assume a fine blue.[2579]
[2577] Flückiger, _Crystalline Principles in Aloes_,—_Pharm. Journ._
September 2, 1871. 195.
[2578] Rapidly fading in the case of barbaloïn, but permanent with
nataloïn unless heat be applied.
[2579] These reactions may be sometimes got even with the crude drugs.
The researches of E. von Sommaruga and Egger in Vienna (1874) have been
directed in particular to the aloïn of Socotrine aloes. The melting
point of this aloïn was found to be between 118° and 120° C., that
of barbaloïn being much higher. The authors conclude that the three
form an homologous series, that their composition may probably be
represented thus:—
Barbaloïn C₁₇H₂₀O₇
Nataloïn C₁₆H₁₈O₇
Socaloïn C₁₅H₁₆O₇
They derive in all probability from anthracene, C₁₄H₁₀.
The portion of aloes insoluble in cold water was formerly distinguished
as _Resin of Aloes_, from the soluble portion which was called _Bitter
of aloes_ or _Aloëtin_. From the labours of Kossmann (1863), these
portions appear to have nearly the same composition. The soluble
portions treated with dilute sulphuric acid, is said to yield
_Aloëresic_ and _Aloëretic Acids_, both crystallizable, besides the
indifferent substance _Aloëretin_. These observations have not to our
knowledge been confirmed.
It has been shown by Tilden and Rammell[2580] that the _Resin of Aloes_
may by prolonged treatment with boiling water be separated into two
bodies, which they distinguish as _Soluble Resin A._ and _Insoluble
Resin B._ With the first it is possible to form a brominated compound,
which though non-crystalline is apparently of definite composition. In
the view of these chemists the _Resin A._ is a kind of anhydride of
barbaloïn—Barbaloïn, 2(C₃₄H₃₆O₁₄) less H₂O = Aloe Resin A., C₆₈H₇₀O₂₇.
The resin boiled with nitric acid yields a large amount of chrysammic
acid, together with picric and oxalic acids, and carbonic anhydride.
_Insoluble Resin B._ was found to have nearly the same composition as
_Resin A._
[2580] _Pharm. Journ._ Sept. 21, 1872. 235.
Aloes treated with various reagents affords a number of remarkable
products. Thus, according to Rochleder and Czumpelick (1861) it yields,
when boiled with soda-lye, colourless crystals an inch long, which
appear to consist of a salt of _Paracumaric Acid_, together with small
quantities of fragrant essential oils and volatile fatty acids.
When boiled with dilute sulphuric acid, aloes yields paracumaric acid,
from which by fusion with caustic potash, as also directly from aloes,
Hlasiwetz (1865) obtained _Para-oxybenzoic Acid_ (p. 408). Weselsky
(1872-73) has shown that accompanying the last two products, there is a
peculiar, crystallizable acid, C₉H₁₀O₃, which he has named _Alorcinic
Acid_.
By distillation with quicklime, E. Robiquet (1846) obtained _Aloïsol_,
a yellowish oil, which Rembold (1866) proved to be a mixture of
dimethylated phenol (_Xylenol_)
{(CH₃)₂
C₇H₃ {, with acetone and hydrocarbons.
{OH
Nitric acid forms with Barbadoes aloes, but still better, as Tilden
has shown, with barbaloïn, _Aloëtic Acid_, C₁₄H₄(NO₂)₄O₂, _Chrysammic
Acid_, C₁₄H₄(NO₂)₄O₄, and finally _Picric Acid_, together with _Oxalic
Acid_. The first two of these acids are distinguished by the splendid
tints of their salts, which might be utilized in dyeing.
Chlorine, passed into an aqueous solution of aloes, forms a variety of
substitution-products, and finally _Chloranil_, C₆Cl₄O₂.
When somewhat strongly heated, aloes swells up considerably, and after
ignition leaves a light, slow-burning charcoal, almost free from
inorganic constituents. Ordinary Cape aloes, for example, dried at 100°
C., leaves only 1 per cent. of ash.
=Commerce=—There were imported into the United Kingdom in the year
1870, 6264 cwt. of aloes. Of this quantity, South Africa shipped 4811
cwt.; and Barbados 970 cwt. The remainder was probably furnished by
Eastern Africa.
The commercial value of the varieties of aloes is very different.
In 1874, _Barbados Aloes_ was quoted in price-currents at £3 5_s._
to £9 10_s._ per cwt.; _Socotrine_ at £5 to £13; while _Cape Aloes_
was offered at £1 10_s._ to £2. In England, the first two alone
are allowed for pharmaceutical preparations. Even the _Veterinary
Pharmacopœia_[2581] names only _Aloë Barbadensis_. Cape Aloes is
esteemed on the Continent, and chiefly consumed there.
=Use=—Aloes is a valuable purgative in very common use, it is generally
given combined with other drugs.
=Adulteration=—The physical characters of aloes, such as colour of the
powder, odour, consistence and freedom from obvious impurity, coupled
with its solubility in weak alcohol, usually suffice for determining
its goodness.