Chapter C: W. HEATON, F.I.C., F.C.S., Lecturer on Chemistry at the (10)

_Prep., &c._ No General rules can be given for this purpose. Alloys of metals differing greatly in fusibility, are commonly made by adding the more fusible one, either in the melted state, or in small portions at a time, to the other melted, or heated to the lowest possible temperature at which a perfect union will take place between them. The mixture is usually affected under a flux, or some material that will promote liquefaction, and prevent volatilisation and unnecessary exposure to the air. Thus, in melting lead and tin together, for solder, resin, or tallow is thrown upon the surface; in tinning copper, the surface is rubbed with sal ammoniac; and in combining some metals, powdered charcoal is used for the same purpose. Quicksilver combines with many metals in the cold, forming AMALGAMS.

_Comp._ The following _Table_ exhibits the composition of the more important compounds of this class:--

_Table of the principal Alloys._[27]

NAMES. COMBINING METALS.

ALBATA See German Silver.
AMALGAMS Mercury and other metals.
BATH-METAL Copper and zinc.
BELL-METAL Copper and tin.
BRASS Copper and zinc.
BRITANNIA METAL Tin with antimony, copper, and bismuth.
BRONZE Tin and copper.
BRONZE ALUMINIUM Copper and aluminium.
CANNON-METAL Tin and copper.
DUTCH GOLD Copper and zinc.
FUSIBLE METAL Bismuth, lead, and tin.
GERMAN SILVER Copper, nickel, and zinc, with,
sometimes, a little iron and tin.
GOLD (_standard_) Gold with copper.
GOLD (_old standard_) Gold with copper and silver.
GUN-METAL See Cannon-metal.
MOSAIC GOLD Copper and zinc.
OR-MOLU Copper and zinc.
PEWTER (_common_) Tin and lead.
PEWTER (_best_) Tin with antimony, bismuth and copper.
POT-METAL, COCK-METAL Copper and lead, with,
sometimes, a little zinc.
QUEEN'S METAL Tin with antimony, bismuth, and copper.
SHOT-METAL Lead with a little arsenic.
SILVER (_standard_) Silver and copper.
SOLDER Tin and lead.
SPECULUM-METAL Tin and copper, and arsenic.
STEREOTYPE-METAL Lead, antimony, and bismuth.
TOMBAC, RED TOMBAC Copper and zinc.
TUTANIA See Britannia metal.
TYPE-METAL Lead and antimony.
WHITE COPPER (_Packfong_; Copper and arsenic.
_Whitetombac_)

[Footnote 27: For the proportions of the component metals, refer to the alloys under their respective heads.]

_Prop., &c._ Alloys generally possess characteristics unshared by their component metals. Thus, copper and zinc form brass, which has a different density, hardness, and colour to either of its constituents. Whether the metals tend to unite in atomic proportions, or in any definite ratio, is still undetermined. The evidence afforded by the natural alloys of gold and silver, and by the phenomena accompanying the cooling of several alloys from the state of fusion, goes far to prove that such is the case. (Rudberg.) The subject is, however, one of considerable difficulty, as metals and metallic compounds are generally soluble in each other, and unite by a simple fusion and contact. That they do not combine indifferently with each other, but exercise a species of elective affinity not dissimilar to other bodies, is clearly shown by the homogeneity and superior quality of many alloys in which the constituent metals are in atomic proportions. The variation of the specific gravity and melting-points of alloys from the mean of those of their component metals, also affords strong evidence of a chemical change having taken place. Thus, alloys generally melt at lower temperatures than those required for their separate metals. They also usually possess more tenacity and hardness than the mean of their constituents.

Matthiessen found that when weights are suspend to spirals of hard-drawn wire made of copper, silver, gold, or platinum, they become nearly straightened when stretched by a moderate weight; but wires of equal dimensions composed of copper-tin (12% of tin), silver-platinum (36% of platinum), and gold-copper (84% of copper), scarcely undergo any permanent change in form when subjected to tension by the same weight.

The same chemist gives the following approximative results upon the tenacity of certain metals and wires hard drawn through the same gauge (No. 23):

Breaking strain for:

lbs.
Copper 25-30
Tin under 7
Lead " 7
Tin-lead (20% lead) about 7
Tin-copper (12% copper) " 7
Copper-tin (12% tin) " 80-90
Gold 20-25
Gold-copper (8·4% copper) 70-75
Silver 45-50
Platinum 45-50
Silver-platinum (30% platinum) 75-80

On the other hand, their malleability, ductility, and power of resisting oxygen is generally diminished. The alloy formed of two brittle metals is always brittle; that of a brittle and a ductile metal, generally so; and even two ductile metals sometimes unite to form a brittle compound. The alloys formed of metals having different fusing-points are usually malleable whilst cold, and brittle whilst hot. The action of the air on alloys is generally less than on their simple metals, unless the former are heated. A mixture of 1 part of tin and 3 parts of lead is scarcely acted on at common temperatures; but at a red heat it readily takes fire, and continues to burn for some time like a piece of bad turf. In like manner, a mixture of tin and zinc, when strongly heated, decomposes both moist air and steam with almost fearful rapidity.

The specific gravity of alloys is never the arithmetical mean of that of their constituents, as commonly taught; and in many cases considerable condensation or expansion occurs. When there is a strong affinity between two metals, the density of their alloy is generally greater than the calculated mean; and _vice versâ_, as may be seen in the following Table:--

_Alloys having a density_--

Greater than the mean of Less than the mean
their constituents:-- of their constituents:--

Copper and bismuth, Gold and copper,
" palladium, " iridium,
" tin, " iron,
" zinc, " lead,
Gold and antimony, " nickel,
" bismuth, " silver,
" cobalt, Iron and antimony,
" tin, " bismuth,
" zinc, " lead,
Lead and antimony, Nickel and arsenic,
Palladium and bismuth, Silver and copper,
Platinum and molybdenum, Tin and antimony,
Silver and antimony, " lead,
" bismuth, " palladium,
" lead, Zinc and antimony.
" tin,
" zinc.

"Every alloy," says Dr Ure, "is, in reference to the arts and manufactures, a new metal, on account of its chemical and physical properties. A vast field here remains to be explored. Not above sixty alloys have been studied by chemists, out of many hundreds which may be made, and of these very few have yet been practically employed. Very slight modifications often constitute very valuable improvements upon metallic bodies." See ANALYSIS, ASSAYING, BRASS, BRONZE, ELECTROTYPE, GERMAN SILVER, GOLD, METALS, SPECIFIC GRAVITY, &c.

=ALL'SPICE.= See PIMENTO.

=ALLU''VIAL.= (-l'[=o][=o]v'-y[)a]l). _Syn._ ALLU''VIOUS*; ALLU''VIUS, L.; D'ALLUVION, Fr. In _geology_, applied to partial deposits of mud, sand, gravel, &c., left by rivers and floods upon land not permanently submerged beneath water; in _agriculture_, applied to soils so formed or deposited.

=ALLU''VIUM.= [L., Eng.] _Syn._ ALLUVION, Fr.; ANFLÖSSUNG, ANSCHWEMMUNG, Ger. In _geol._ and _agr._, alluvial deposit or soil. See SOILS, &c.

=AL'LYL= (-l[)i]l). C_{3}H_{5}. In _chemistry_, the radical of the essential oils containing sulphur, as those of assaf[oe]tida, garlic, horseradish, mustard, onions, &c., which are either sulphides or sulphocyanides of allyl. Its probable existence was first shown by Captain Reynolds, who succeeded in producing several of its derivatives. It has since been obtained, in a separate state, by the action of sodium upon iodide of allyl. It is an oily substance with a high boiling point.

=Allyl, Sulphide of=, (C_{3}H_{5})_{2}S; obtained (artificially) by acting on sulphocyanide of allyl with sulphide of potassium. See OIL OF GARLICK.

=Allyl, Sulphocy'anide of=, C_{3}H_{5}CNS; obtained by submitting iodide of allyl to the action of sulphocyanide of potassium; or by gently heating a mixed alcoholic solution of sulphide of allyl and bichloride of mercury, with sulphocyanide of potassium. See OIL OF MUSTARD (VOLATILE).

=AL'MOND= (ah'-m[)u]nd). _Syn._ AMYG'DALA (also -US, -UM*), L.; AMANDE, Fr.; MANDEL, Ger., Dut., Dan., Swed. The 'almond-tree' (_amyg'dalus commu'nis_--Linn.; Ph. L., E., and D.; _Amandier_--Fr.), a tree of the nat. ord. Rosaceæ, indigenous to Persia, Syria, and the north of Africa; but also extensively cultivated in southern Europe. The almond-tree is about the size of the peach-tree, which it much resembles in appearance. It is incapable of ripening its fruit in this country, and is, therefore, only grown here for the sake of its beautiful vernal flowers. There are several varieties, of which the most important are the sweet and the bitter, so named from the flavour of the seed or kernel. These, for the most part, resemble each other in appearance. De Candolle ('Prodromus,' ii, 530) gives five varieties of this species:--A. AMA''RA (_bitter-almond_); A. DUL'CIS (_sweet-a._); A. FRAGILIS (_tender-shelled a._); A. MACROCAR'PA (_large-fruited a._, _pista'chio a._, _sultana a._); A. PERSICO'ÏDES (_peach a._).

=Almond, Per'sian.= The peach.

=AL'MONDS=. _Syn._ AMYG'DALÆ, L.; AMANDES, Fr.; MANDELN, Ger. The seed or kernels of the almond-tree. They are met with in commerce both in the shell (AMYG'DALÆ CUM PUTAM'INE, -[)i]n-e, L.), and shelled (AMYGDALÆ, L.). In the retail shops, most commonly in the latter form. Those rancid, broken, or worm-eaten should be rejected.

=Almonds, Bitt'er.= _Syn._ AMYG'DALÆ AMA''RÆ, L.; AMYGDALA AMARA, Ph. E.; AMANDES AMÈRES, Fr.; BITTERE MANDELN, Ger. A variety imported from Mogadore, chiefly characterised by possessing the bitter flavour, and when rubbed with water, the odour of peach-kernels. They are also smaller and thicker than the sweet almond.

_Uses, &c._ Bitter almonds are used to relieve the flavour of sweet almonds, to clear muddy water, and to flavour confectionery, liqueurs, &c. By pressure, they yield their bland oil (OIL OF ALMONDS; O'LEUM AMYG'DALÆ, L.); the resulting cake (BITTER-A. CAKE; PLACEN'TA A. AMARÆ, L.) is distilled for the volatile oil (ESSENTIAL OIL OF A.; O. A. A., L.), and is afterwards again pressed into cakes (A.-CAKE), and used to fatten pigs, and for other purposes. Bitter almonds are now seldom employed in medicines, although it is said that they have cured 'intermittents' when bark had failed (Bergius), and that their emulsion has been found useful in pulmonary and dyspeptic affections, hooping-cough, and asthma; and externally as a lotion in acne. (Thomson.) In large quantities they are poisonous, and even in the smallest quantities have been known to produce nettle-rash (_urticaria_) and other unpleasant symptoms. They have long been in repute as an antidote to intoxication. The ancient bacchanals chewed them at their orgies, to lessen the effects of wine, and to enable them to take it in larger quantities with impunity.

=Almonds, Blanched'= (bl[)a]ncht'-). _Syn._ AMYG'DALÆ DECORTICA'TÆ, L. Almonds from which the husk or seed-coat has been removed. This is effected by soaking them for a short time in warm water, until the skin can be easily removed by pressure between the thumb and forefinger. They are then peeled, rinsed in cold water, drained, and dried. When intended for the table, the last is effected by wiping them with a soft towel; but when they are intended to be powdered, or kept, they are dried by a very gentle heat in a stove, or in the sun.

=Almonds, Burnt'.= _Syn._ ROASTED ALMONDS; ALMOND COFFEE. Used to colour and flavour liqueurs and confectionery; and formerly, as a substitute for coffee.

=Almonds, Guia'na.= (g_h_e-[=a]_h_'-n[)a]; _g_ hard). Brazil-nuts.

=Al'monds, In'dian.= The fruit of _terminalia catappa_ (Linn.). They are oleaginous, and nutritious; and are used as a substitute for almonds.

=Almonds, Ja'va= (j[=a]_h_'-). The nuts or kernels of _canarium commune_ (Linn.). They are eaten, made into bread, and pressed for their oil.

=Almonds, Sweet'.= _Syn._ ALMONDS; AMYG'DALÆ, L.; A. DULCES, Ph. D.; AMYGDALA, A. JORDAN'ICA, Ph. L.; A. DULCIS, Ph. E., & Ph. L. 1836; AMANDES, AMANDES DOUCES, Fr.; SÜSSE MANDELN, Ger. These are the well-known dessert or table fruit of the name, and are the kind always referred to when 'almonds' (simply) are spoken of or ordered.

_Comm. var._--1. JOR'DAN ALMONDS, which are the finest, and are imported from Malaga. Of these there are two kinds; the one, above an inch in length, flat, and with a clear brown cuticle, sweet, mucilaginous, and rather tough; the other, more plump, and pointed at one end, brittle, but equally sweet with the former.--2. VALEN'TIA A. (which come next in quality) are about 3/8ths of an inch broad, not quite an inch long, round at one end, and obtusely pointed at the other, flat, of a dingy brown colour, with a dusty cuticle.--3. BAR'BARY and ITAL'IAN A., which resemble the latter, but are generally smaller and less flattened.--4. A variety, of medium quality, imported in baskets from Spain.

_Uses, &c._ Sweet almonds are nutritive, emollient, and demulcent; but frequently disagree with weak stomachs. The husk is apt to occasion indigestion and nausea. Owing to a peculiar idiosyncrasy of some habits, dyspepsia, diarrh[oe]a, [oe]dematous swelling of the face, and urticaria (_nettle-rash_), sometimes, though seldom, follow the use of unblanched almonds. Blanched almonds do not produce these inconveniences, and, therefore, should be preferred for the table. In _medicine_, almonds are employed chiefly under the form of emulsion, confection, &c., and to suspend oily substances in water. Their uses for dietetical purposes are well known. Preparations of them are also employed as cosmetics. The cake left after expressing the oil (ALMOND-CAKE) is used for washing the skin, which it is said to render beautifully soft and clear. See ALMOND PASTE, &c.

=AL'NIGHT=[dagger] (awl'-). A cake of wax with a wick in the midst. The forerunner of, and a rude form of the modern dumpy night-lights called MORTARS.

=AL'OE= ([)a]l'-o). _Syn._ AL'OË (-o-[=e]), L., Fr. (or ALOÈS), Ger., Ital., Sp., Belg., Dan., Dut., Swed. The aloe-tree. In _botany_, a genus of plants of the nat. ord. Liliaceæ (DC). The species, of which there are several, are succulent plants or small trees with endogenous stems, and stiff, fleshy, hard, pointed leaves, abounding in a purgative principle (ALOES), which is obtained from them by either evaporating the expressed juice or the decoction. They are all natives of warm climates, and most of them are indigenous to southern Africa.

_Hist._ [Hebrew: a-ènx], _aehleem_ (aloe-trees), were known to the sacred historians; and both the plant and the inspissated juice are described by Dioscorides[28] and Pliny.[29]

[Footnote 28: Lib. iii, c. xxv.]

[Footnote 29: 'Hist. Nat.,' lib. xxvii, c. v.]

_Uses, &c._ In Africa, the leaves of the Guinea aloe are made into ropes, fishing-lines, bow-strings, stockings, hammocks, &c. The leaves of another species are used to catch and hold rain-water. The expressed juice and decoction are also used by the natives as a distaff. (Vide _infrà_.) Comparative trials, made in Paris, of the strength of cordage and cables formed of hemp, and of the aloe from Algiers, are said to have shown the great superiority of the latter. Fabroni obtained a fine violet colour from the recent juice of the aloe, which has been proposed as a dye for silk.[30]

[Footnote 30: 'Annales de Chimie,' xxv, 305.]

=American Aloe.= The _agave Americana_ (Linn.) is a plant unconnected with the preceding, and belonging to the nat. ord. Bromeliaceæ. It is found in all parts of tropical America, and is largely cultivated on the shores of the Mediterranean; and less frequently, as an exotic plant in this country. It grows to the height of about 20 feet, and takes many years to produce its gigantic and magnificent pyramid of flowers; shortly after which it perishes, exhausted, as it were, by its efforts in bestowing its rare beauty on the floral world. The vulgar belief is that it blossoms only once in a century; but, as stated by the late Mr Loudon, it flowers sooner or later according to the culture bestowed on it. Its sap yields a kind of honey (AGAVE HONEY), and by fermentation an intoxicating liquor (PULQUE); desiccated juice, mixed with wood ashes, is used as soap, and lathers either with sea or fresh water; leaf-fibre, used as hemp to make thread and twine.

=AL'OE-RESIN.= _Syn._ RESI'NA AL'OËS, L. The resinous matter deposited by a decoction of aloes as it cools.

_Prep._ (Ph. L. 1746.) Boil aloes, 1 part, in water, 8 parts, and allow the decoction, strained whilst hot, to repose until the next day; then wash the deposited RESIN, and dry it by a gentle heat. It is probably a mixture of aloine and oxidised extractive.

=AL'OES= (-[=o]ze). _Syn._ BITT'ER ALOES[double-dagger]; AL'OË (-o-[=e]), L.; ALOÈS, SUC D'ALOÈS, Fr.; ALOE, GLAUSINDE ALOE, Ger.[31] The inspissated juice or extract of several species of aloe.

[Footnote 31: Also see ALOE, (above).]

_Comp., Prep., &c._ Aloes is a complex resinous substance containing a body called aloin, which is its active or purgative principle. It is completely soluble in boiling water, and in alcohol or rectified spirit. The decoction deposits an impure resin or resinoid on cooling.

_Phys. eff., Uses, &c._ Aloes is a warm stimulating purgative, in doses of 3 to 10 gr.; whilst even 1 or 2 gr. seldom fail to produce one motion without pain or inconvenience. It is considered highly serviceable in hypochondriacal, hysterical, and dyspeptic affections, particularly in phlegmatic habits, and in cases arising from deficiency of bile. As an emmenagogue, and a vermifuge, few medicines are more valuable. It acts on the large intestines, and principally on the rectum; and, therefore, should be administered with caution, or only in small doses, where there is a tendency to prolapsus or piles, and in cases where uterine stimulants (as in pregnancy, &c.) would be improper. "It is remarkable with regard to it, that it operates almost to as good a purpose in a small as in a large dose; and one or two grains will produce one considerable dejection, and twenty grains will do no more, except it be that in the last dose (case) the operation will be attended with griping, &c. It is one of the best cures for habitual costiveness." (Cullen.) Many of the effects complained of arise from its slow solubility in the primæ viæ, and may be obviated by administering it in a liquid form, or in a solid form combined with soap, which renders it freely soluble in the juices of the stomach.

Aloes is more frequently taken than, perhaps, any known purgative. It enters into the composition of a majority of the aperient medicines prescribed by the faculty, and forms the principal ingredient of nearly all the advertised purgative, antibilious, and universal pills of the nostrum-mongers. The fact of aloetic pills not acting until about 8 to 10 hours after being swallowed--so that if taken on retiring to rest at night they do not generally disturb the patient before the usual time of rising in the morning--has contributed more than anything else to make such remedies popular with parties whose habits or business avocations would be otherwise interfered with.

Aloes is also extensively used in veterinary practice. It is the most valuable and reliable purgative for the horse of the whole materia medica; but is less to be depended on for cattle, sheep, and hogs. Barbadoes aloes is the best for this purpose. Cape aloes are, however, often employed, when 1-4th more must be given.--_Dose_ (of the former), for a HORSE, 4 to 8 dr.;[32]--CATTLE, 3 to 6 dr. (followed by a purging drench);--HOGS, 5 to 15 gr.;--SHEEP, 15 to 30 gr.;[33]--DOGS (small ones), 10 to 30 gr., (middle-sized) 20 to 44, or even 60 gr., (large) 3/4 to 1 dr., or even 2 dr.

[Footnote 32: Aloes takes from 18 to 30, or even 36 hours, to operate on a horse.]

[Footnote 33: Aloes, however large the dose, often fails to purge sheep. In very large quantities it is poisonous to them.]

Aloes is also used in dyeing; and as a colouring matter in stains, lacquers, and varnishes. Aloes, and several of its preparations, are likewise extensively employed to adulterate porter.

_Var._ These, arranged in the order of their reputed medicinal value, are--Socotrine, Hepatic, Barbadoes, Cape, &c.; and alphabetically, as given below:--

=Aloes, Barba'does.= _Syn._ ALOES IN GOURDS; AL'OË BARBADEN'SIS, L., Ph. L. & E. Imported from Barbadoes and Jamaica, usually in gourds; sometimes in boxes. The best is the inspissated juice of the cut leaf of _aloë vulga''ris_; an inferior quality is prepared from the decoction.--_Char., &c._ Opaque, lustreless, of a liver colour, a little tending to black, with a bitter nauseous taste, and a very disagreeable odour, especially when breathed on; powder a dull olive-yellow. It is the 'hepatic' aloes of most continental writers, and said to be the [Greek: Aloê] of Dioscorides. It is more active than the other varieties of aloes; but is also more apt to occasion hæmorrhoids, and to gripe, than any of them.

=Aloes, Cab'alline= (-l[=i]ne.) _Syn._ F[OE]T'ID ALOES, HORSE A.; ALOË CABALLI'NA, A. GUINIEN'SIS, L.; ALOÈS CABALLIN, Fr. From _aloë In'dica_ (O'Shaughnessy); or from _aloë spica'ta_ by long and careful boiling. (Lindley.) Used only by farriers. Scarcely known in English commerce.

=Aloes, Cape.= _Syn._ ALOË CAPEN'SIS, A. LU'CIDA (_Geiger_), L. Imported from the Cape of Good Hope, and obtained from _aloë spica'ta_, and other Cape species. Odour stronger and even more disagreeable than that of Barbadoes aloes; colour deep greenish-brown; appearance shining and resinous; fracture generally glassy; powder a lively greenish-yellow; almost completely soluble in boiling water, decoction paler than that of other kinds. It is weaker than Barbadoes or even hepatic aloes, and is more apt to gripe, &c., than the latter. A finer kind, known as '_Bethelsdorp aloes_,' imported from Algoa Bay, is more of a liver colour, and softer than the preceding, and hence often called CAPE HEPATIC-ALOES.

=Aloes, Hepat'ic.= _Syn._ BOMBAY' ALOES*, EAST-INDIA A.*, LIVER-COLOURED SOCOTRINE A.*; ALOË HEPAT'ICA, Ph. L. & D.; A. IN'DICA, Ph. E. Imported from Bombay and Madras. It is usually said to be obtained from "uncertain species of aloes;" but it is almost certain that it is "the juice of the Socotrine aloes plant which has been solidified without the aid of artificial heat."[34]--_Char., &c._ "Opaque, of a liver colour, bitter taste, and an unpleasant odour." (Ph. L.) It is less odorous, darker coloured, and more opaque than Socotrine aloes; its powder has also a duller colour, and weak spirit leaves much undissolved matter. Its decoction on cooling frequently deposits a yellow powder. The finer and brighter varieties of hepatic aloes are commonly sold for 'Socotrines,' and their medicinal virtues are nearly similar. (See _below._)

[Footnote 34: Pereira, 'Elem. Mat. Med. and Therap.,' vol. ii, 188, 4th Ed.; 'Pharm. Journ.,' vol. xi.]

=Aloes, In'dian= (various);--1. Deep brown or black, very opaque, and less soluble than ordinary aloes. Scarcely known in commerce.--2. Several varieties ranging in character from 'Cape aloes' to 'hepatics,' and occasionally to 'Barbadoes,' obtained from several species.

=Aloes, Mo'cha= (-k[)a]h). _Syn._ ALOË DE MOCHÂ, L. Imported from Muscat. An inferior kind of Indian aloes. (Christison.) It is obtained from the same plant as produces genuine hepatic aloes. (Lindley.) It holds an intermediate position between 'Cape' and 'hepatics,' but contains much impurity; the latter often amounting to upwards of 25%. Some specimens are, however, of excellent quality. When melted and 'doctored,' it is sold for Barbadoes, hepatic, and even Socotrine aloes.

=Aloes, Soc'otrine= (-tr[)i]n; s[)u]k'-[double-dagger]). _Syn._ SOC'OTORINE ALOES, SMYR'NA A., TUR'KEY A.; ALOË SOCOTRI'NA, Ph. L.; ALOË, Ph. L. 1836; A. SOCOTRI'NA, Ph. E. "The juice of the cut leaf of uncertain species hardened by the air." (Ph. L.) Genuine Socotrine aloes is generally supposed to be obtained from _aloë spica'ta_; but is referred by De Candolle to a distinct species, A. SOCOTRI'NA; and by Martius, also to _a. purpuras'cens_. Formerly this variety was brought from the Island of Socotra or Zocotora (hence the name), by way of Smyrna and Malta; but it is now chiefly obtained from Bombay and Madras.--_Char., &c._ Colour garnet red to golden red; smell peculiar and aromatic, not unlike a decaying russet apple, especially when fresh-broken, or breathed on, or warmed; taste permanently and intensely bitter; fracture conchoidal; softens in the hand, and becomes adhesive, yet retains considerable brittleness; powder bright golden-yellow colour; central portions of the lumps often soft, especially when first imported. "It is brittle, bitter, of a reddish-brown colour, and an aromatic odour. Light permeates thin recently broken laminæ." (Ph. L.) "In thin pieces, translucent and garnet red; almost entirely soluble in spirit of the strength of sherry. Very rare." (Ph. E.)

Socotrine aloes are always preferred for medicinal purposes, and are the only variety used in perfumery, varnishes, and other nice purposes in the arts.

=Aloes, Strained.= _Syn._ MELTED ALOES; ALOË COLA'TA, L. _Proc._ 1. The aloes are melted in a copper pan, by the heat of steam or a water bath, and are then pressed through a strong hair or wire sieve, and allowed to cool.

2. As above, but with the addition of about twice its weight of water; the decoction being strained and evaporated.

_Obs._ Mocha, Indian, and other common aloes, treated in this way and coloured, are frequently sold for melted or strained 'Socotrines' and 'hepatics.' The colouring matter usually employed is the precipitated carbonate of iron (sesquioxide), or Venetian red, in very fine powder, with, sometimes, a little annatto. This fraud is not readily detected by mere inspection, by those unaccustomed to these matters; and hence the impunity with which it is perpetrated.

The object in melting aloes is to deprive it of the foreign matters, as sand, leaves, pieces of wood, &c., which the commoner kinds generally contain in large quantities. The action of the heat drives off much of their nauseous smell, at the same time that it deepens their colour, and renders their appearance more translucent and resinous, to the disguise of their original nature. The operation, on the large scale, is usually carried on at night, in consequence of the horribly nauseous fumes evolved, which may be smelt at a great distance, and contaminate the clothes of those engaged in it for a long time afterwards.

=AL'OES HEMP.= A plant growing in Peru, the East and West Indies, and Mexico (_A. Americana_, _A. vivapara_, _A. f[oe]tida, &c._), where the leaf is cultivated for its fibre, which is generally of a yellowish-white colour, and used for rope-making.

=AL'OES WOOD.= _Syn._ AL'OE-WOOD; EAGLEWOOD; AGAL'LOCHUM (-k[)u]m), LIG'NUM AL'OËS, L. AGAL'LOCHI, L. A. VE''RI, L. AQ'UILÆ, L. ASPAL'ATHI, L.; AGALLOCHE, BOIS D'ALOÈS, Fr.; ALOEHOLZ, Ger.; CALAM'BAC, CALAM'BOUC, Ind.; XYLO-AL'OËS[dagger]. A name applied to the wood of _alöex'ylon agal'lochum_ (Lam.), a leguminous tree of Cochin China; and, though apparently less correctly, to that of _aquila''ria agallochum_ and _a. ova'ta_ (Lour.), trees of tropical Asia, belonging to a different nat. order. Both are highly fragrant and aromatic; used in fumigations and pastilles, and occasionally by cabinet makers and inlayers. The essential oil of the wood, dissolved in spirit, was regarded by Hoffmann as one of the best cordials and invigorants known. The same has also been said of a tincture of its resin.

The same name and synonyms are popularly applied to the resin of the above woods (ALOES-WOOD RESIN), of which there are two varieties:--the one, light and porous, and filled with a highly fragrant resinous substance; the other, denser and less resinous. It is an oily concretion in the centre of the tree, the result of disease, which gradually hardens, and, in time, kills it. It is highly fragrant, and is said to be nervine, cephalic, cardiac, and stimulant. The powder is regarded as tonic and astringent. Of all perfumes this is said to be the one most esteemed by oriental nations.

=ALOE'TIC.= _Syn._ ALOËT'ICUS, L.; ALOÉTIQUE, Fr. Of or belonging to aloes. In _medicine_, _pharmacy_, &c., applied to any preparation containing aloes as a characteristic ingredient; made or obtained from aloes. Substantively, an aloetic medicine.

=AL'OIN= (-o-[)i]n). C_{17}H_{18}O_{7}. [Eng., Fr.] _Syn._ AL'ÖIN; ALOÏ'NA, L. The Messrs T. & H. Smith, of Edinburgh, have applied this name to a crystalline substance, which they assert to be the pure cathartic principle of aloes. Their process is to evaporate to the consistence of a syrup, in vacuo, a solution obtained by exhausting a mixture of aloes and sand, with cold water, and then to set it aside for a few days. The resulting dark crystalline mass is purified by pressure between folds of bibulous paper, and repeated crystallisation from hot water. Barbadoes aloes are commonly used for the purpose; but soft or semi-liquid Socotrine aloes, or the unevaporated Socotrine-aloes juice, is probably its best source. Tilden gives the following process for the preparation of aloin:--The aloes crushed small is to be dissolved in nine or ten times its weight of boiling water acidified with sulphuric acid. After cooling and standing for a few hours, the clear liquid is decanted from the resin, and evaporated. The concentrated solution deposits a mass of yellow crystals, which can be purified by washing, pressure, and recrystallisation from hot spirit. After several recrystallisations the aloin is obtained in the form of beautiful yellow needles, which are pretty soluble in water and in alcohol, but soluble with difficulty in ether.--_Dose_, 1 to 2 gr.

=ALOPE'CIA= (-sh'[)a]). [L.] _Syn._ AL'OPECY, FOX'-EVIL; ALOPÉCIE, Fr.; FUCHSRAUDE, Ger. In _pathology_, baldness from disease, often extending to the beard and eyebrows; as distinguished from 'calvities,' or ordinary baldness arising from attenuation of the scalp or defective nutrition. See BALDNESS.

=ALPAC'A.= A species of Llama, popularly known as the PERUVIAN SHEEP, an animal intermediate between the camel and sheep, having long silky hair, nearly as fine as that of the Cashmere goat. It was introduced to the British manufacturers in 1834, when only 5700 lbs. of it was imported; but it soon became an important article of commerce, the quantity imported having gradually risen to above 2-1/4 millions of lbs. in 1853; whilst the price has risen from about 9d. to 2s. 7d. the lb., in the same time. The name is also given to fabrics woven from the wool of this animal; and to others in fine wool, made in imitation of them. The gigantic factory, &c., erected at Saltaire, Yorkshire, in 1852, for this manufacture, covers about 12 acres of land. See LLAMA.

=ALPENKRAUTER-BRUST-TEIG= (Grablowitz, Gras). Pectoral cakes of Alpine herbs. Gum arabic, 100 parts; sugar, 200 parts; extract liquorice, 1 part; saffron, 1/8th part. Each box contains 48 lozenge-shaped yellowish cakes. Made into a mass with decoction of marsh mallow. (Hager.)

=ALPENKRAUTER GESUNDHEIT'S LIQUEUR= (Rudolph Bohl). Medicinal liqueur of Alpine herbs. A bottle containing 350 grammes of a liqueur which is an extract of star anise, cassia, frangula bark, centaury, chicory, gentian, and a little aloes. (Hager.)

=ALPENKRAUTER-MAGENBITTER= (Hauber). Stomachic bitters of Alpine herbs. A brown liqueur of bitter, spirituous, and slightly aromatic flavour, containing in 100 parts: oil of anise, 0·5; oil of cloves, 0·5; aloes, 1·5; alcohol, 40; water, 50. 157 grammes in each bottle. (Wittstein.)

=ALPHA-ORSELL'IC ACID.= See ORSELLIC ACID.

=ALPINE ROSE SOAP, SWISS.= A preservative against syphilitic infection (G. A. Sarpe, Zurich). A glass cylinder corked and sealed, about 2 inches long, and containing a hard brownish-grey mass weighing 12 grammes, prepared thus:--Ammonia, 1 part; sublimate, 3 parts; tannin, 2 parts; chloride of lime, 24 parts; Castile soap, 190 parts; oil of cloves, 1 part; spirit of wine, q. s. (Hager.)

=AL'QUIFOU= (-ke-f[=o][=o]). _Syn._ BLACK LEAD-ORE, POTTER'S ORE. A native sulphide of lead used by potters to give a green glaze to coarse wares.

=ALSTONIA SCHOLARIS.= (Ind. Ph.) _Habitat._ Common in forests throughout India.--_Officinal part._ The bark (_Alstoniæ cortex_). It occurs in thick, irregular, more or less contorted pieces, easily broken. It consists of a rough greyish epidermis, investing a buff or pale cinnamon-coloured bark; internally, still lighter in colour, and of a spongy texture, having a very bitter taste, but devoid of odour.--_Properties._ Astringent, tonic, anthelmintic, antiperiodic--_Therapeutic uses._ In chronic diarrh[oe]a and the advanced stages of dysentery; also as a tonic in debility after fevers, and other exhausting diseases.--_Dose._ 3 to 5 grains, either alone or combined, in bowel affections, with small doses of ipecacuanha and extract of gentian.--_Preparations._ TINCTURE OF ALSTONIA (_Tinctura Alstoniæ_). Take of alstonia bark, bruised, 2-1/2 ounces; proof spirit, 1 pint. Macerate for seven days in a closed vessel, with occasional agitation; filter, and add sufficient proof spirit to make 1 pint. Or prepare by percolation, as Tincture of Calumba.--_Dose_, 1 to 2 fluid drachms.

=Alstonia, Infusion of.= (_Infusum Alstoniæ._) Take of alstonia bark, bruised, 1/2 an ounce; boiling water, 10 fluid ounces. Infuse in a covered vessel for an hour and strain.--_Dose._ From 1 to 2 fluid ounces twice or thrice daily. A good serviceable tonic.

=AL'TERATIVE= (awl'-t[)e]r-[)a]-t[)i]v). _Syn._ AL'TERANT*; AL'TERANS ([)a]l'-), L.; ALTÉRANT, ALTÉRATIF, Fr. In _medicine_, having power to alter; applied to substances and agents which occasion a change in the habit or constitution, and thus re-establish the healthy functions of the body, or any part of it, without producing any sensible evacuation or other obvious effect.

=ALTERATIVE EXTRACT=, or =GOLDEN MEDICAL DISCOVERY= (Dr Pierce, Buffalo), for the cure of all severe, acute, chronic, or long-standing coughs, inflammations, hoarseness, scrofulous, and syphilitic diseases. A clear light-brown fluid, 220 grms., composed of 15 grms. purified honey, 1 grm. extract of lettuce, 2 grms. laudanum, 100 grms. of proof spirit tasting of fusel oil and wood spirit, and 105 grms. water. (Hager.)

=AL'TERATIVES= (-t[)i]vz). _Syn._ ALTERAN'TIA, L.; ALTÉRATIFS, &c., Fr. Alterative medicines or agents. The preparations of mercury and iodine, when properly administered, are the most useful members of this class; and are those which are now the most generally employed.

=ALTHE'IN= ([)a]l-th[=e]'-[)i]n). _Syn._ ALTHÆ'INA, L. The name given by Braconnot to a substance identical with asparagin, which he discovered in the 'marsh-mallow' (_althæ'a officina'lis_, Linn.).

=ALTHOFF WATER= (aqua mirabilis), for torpid ulcers. Wine vinegar, 750 parts; sulphate of copper, 100 parts; potash, 25 parts; ammonia, 30 parts; salt of sorrel, 8 parts; French brandy, 375 parts. Digest for a few days in a glass vessel and distil to dryness from a glass retort. (Wittstein.)

=AL'UDEL= (-[=u]-). In _chemistry_, a pear-shaped glass or earthen pot open at both ends, formerly much used for connecting other vessels in the process of sublimation. A number of them joined together are still employed for the distillation of quicksilver, in Spain.

=AL'UM= K_{2}SO_{4}.Al_{2}(SO_{4})_{3}.24Aq. _Syn._ POT'ASH-ALUM, SUL'PHATE OF ALUMINUM AND POTASSIUM, COMMON ALUM; ALU'MEN, A. POTAS'SICUM, L.; ALUN, SULFATE D'ALUMINE ET DE POTASSE, Fr.; ALAUN, Ger.; ALUME, Ital.

The principal alum-works in England, until recently, were those of Lord Glasgow, at Hurlett and Campsie, near Glasgow, and those of Lords Dundas and Mulgrave, at Whitby, Yorkshire (est. 1600); but those of Mr Spence, at Manchester, and at Goole (Yorkshire), and of Mr Pochin, at Manchester, are now among the largest, if they be not actually the largest in the world. There are also extensive alum-works at and near Newcastle-on-Tyne; but none of importance, that we know of, in any other part of these realms.

_Nat. hist._ Alum is found native in some places (NATIVE ALUM), either effloresced on the surface of bituminous alum-schist (Göttwigg, Austria); or united with the soil in the neighbourhood of volcanoes (Solfatara, Naples); when it may be obtained by simple lixiviation and evaporation, a little potash being commonly added to convert the excess of sulphate of alumina present into alum. It is also found in certain mineral waters (East Indies).

_Sources._ The alum of commerce is usually obtained from schistose pyritic clays, commonly termed alum-ores, aluminous shale, a.-schist, &c.; and from alum-rock, a.-stone, or alunite. At La Tolfa, Civita Vecchia, where the best Roman-alum is produced, the source is stratified alum-stone. On the Continent, and in Great Britain, it is generally pyritaceous clays, volcanic aluminous ores, aluminous shale, or alum-slate. These minerals contain sulphide of iron, alumina, bitumen or carbon, and frequently a salt of potassium. Of late years large quantities of alum have been prepared on the banks of the Tyne from aluminous clay.

_Prep._ The manufacture of alum is technically said to be conducted according to the natural process when prepared from alum-schist or alum-ore; and according to the artificial process when made by acting on clay with sulphuric acid, and adding a potassium salt to the resulting lixivium. The manufacture of alum and of sulphate of alumina from such materials as contain only alumina, to which consequently sulphuric acid and alkaline salts have to be added, has come largely into practice in England. The materials employed are, in addition to clay, cryolite or Greenland spar, a fluoride of aluminum and soda; bauxite, a hydrate of alumina, of more or less purity; and slag. The following are the details of these processes:--

_a._ From ALUM-ORE, ALUMINOUS SCHIST, or SHALE, &c.:--

1. The mineral (alum-ore, a.-schist, &c.) is placed in heaps, and moistened from time to time with water, when it becomes gradually hot, and falls into a pulverulent state. This decomposition commonly occurs either wholly, or partially, on the floor of the mine. If the ore does not possess this property on mere exposure to air and moisture, it is broken into pieces and laid upon a bed of brushwood and small coal, to the depth of about four feet, when the pile is fired and fresh lumps of the alum-mineral thrown on, until the mass becomes of considerable height and size. The combustion, as soon as established, is conducted with a smothered fire, until the calcination is complete; care being taken to prevent fusion, or the disengagement of either sulphurous or sulphuric acid, from contact between the ignited stones and the carbonaceous fuel.[35] To promote these ends the pile, at the proper time, is 'mantled' (as the workmen call it) or covered with a layer of already calcined and exhausted ore, in order to protect it from high winds and heavy rains; as also to moderate the heat, and let it proceed gradually, so that the sulphur present may not be lost or wasted by volatilisation. The roasting is finally checked by a thicker 'mantling,' and the whole allowed to cool. By this time the pile has usually lost about one half its bulk, and become open and porous in the interior, so that the air can circulate freely through the mass; the latter, in dry weather, as the heap cools, being usually promoted by sprinkling a little water on it, which, by carrying down some of the saline matter, renders the interior still more open to the atmosphere. The whole, when cold, or nearly cold, is, if necessary, still further exposed to the action of air and moisture. The time required to calcine the heap properly, including that taken by the burned ore to cool, varies, according to its size and the state of the weather, from three to nine, or even twelve months. The residuum of the calcination is next placed in large stone or brick cisterns, and edulcorated with water, until all the soluble portion is dissolved out; the solution is then concentrated in another stone cistern, so made that the flame and heated air of its reverberatory furnace sweep the whole surface of the liquor. (See _engr._) The evaporation is continued until it just barely reaches the point at which crystals are deposited on cooling; when it is run off into coolers. After the sulphate of iron, always present, has been deposited in crystals, the mother-liquor, containing the sulphate of aluminum, is run into other cisterns, and a saturated solution of chloride of potassium, or of sulphate of potassium, or (sometimes) impure sulphate or carbonate of ammonium, or a mixture of them,[36] is added until a cloud or milkiness ceases to be produced on addition of more.[37] It is next allowed to settle and get thoroughly cold, and the supernatant 'mother-liquor' being drawn off with a pump or syphon, the precipitate, which is alum in the form of minute crystals (technically termed 'flour'), is well drained, and subsequently washed by stirring it up with a little very cold water, which is then drained off, and the operation repeated a second time with fresh water. A saturated solution of the pulverulent alum ('flour') is next formed in a leaden boiler, and the clear portion is run or pumped off, while boiling hot, into crystallising vessels, called roaching casks (see _engr._), the staves of which are lined with lead, and nicely adjusted to each other. After the lapse of a week or ten days, the hoops and staves of these 'casks' are removed, when a thick crust of crystallised alum is found, which exactly corresponds in form and size to the interior of the cask. A few holes are then made in the sides of this mass, near the bottom, to allow the contained mother-liquor to drain off, after which the whole is broken up and packed in casks for sale. Sometimes the alum thus obtained, or the lower portion of it, is washed with a little very cold water, and, if discoloured, or small or slimy, is purified by a second crystallisation.

[Footnote 35: The generality of alum-minerals require roasting; and their own bituminous matter is, in many cases, sufficient to produce the heat required, which need not necessarily exceed 600 to 650° Fahr., provided it be continued for a sufficient period. It is only when they are less bituminous or carbonaceous that slack or saw-dust, &c., is employed.]

[Footnote 36: For pure POTASH-ALUM a salt of potash only must be employed. When ammonia (usually in the form of gas-liquor or gas-sulphate) is used as the precipitant, the product is AMMONIA-ALUM. The ordinary alums of commerce are now generally mixtures of the two.]

[Footnote 37: The respective quantities required to produce 100 parts of alum from the sulphate of alumina liquor are--

Chloride of potassium 15·7
Sulphate of " 18·4
" ammonium 13·9

In practice, the exact quantity required may be found by a previous trial of a little of the aluminous liquor; but the indications mentioned in the text will always show the operator when a sufficient dose is added.]

2. As ammonia-alum (Spence's process; see _below_), but using a potash-salt as the precipitant, either wholly or in part, instead of ammonia; and, in the latter case, supplementing the deficiency of potash with ammonia, as there explained.

_b._ From ALUMINOUS CLAY and OIL OF VITRIOL:--

1. Clay, free or nearly free from carbonate of lime and oxide of iron, is chosen for this purpose. It is moderately calcined (in lumps) in a reverberatory furnace, until it becomes friable; great care being taken that the heat be not sufficient to indurate it, which would destroy its subsequent solubility. It is next reduced to powder, sifted, and mixed with about 45% of its weight of sulphuric acid (sp. gr. 1·45), the operation being conducted in a large stone or brick basin arched over with brickwork. Heat is then applied, the flame and hot air of a reverberatory furnace being made to sweep over the surface of the liquor. The heat and agitation are continued for 2 or 3 days, when the mass is raked out and set aside in a warm place for a few weeks (6 to 8), to allow the acid the more perfectly to combine with the clay. At the end of this time the newly-formed sulphate of alumina is washed out, the solution evaporated until of a sp. gr. of about 1·38 (1·24 for 'ammonia-alum'), and the salt of potash added. The remaining operations resemble those above described. Good alum may be produced by this process at about two thirds the cost of rock or mine alum.

2. (Process of Mr Pochin.) Fine China clay is heated in a furnace, and mixed with a suitable proportion of sulphuric acid; the latter being considerably diluted with water, in order to moderate its action, which would otherwise be far too violent. The mixture is then passed into cisterns furnished with movable sides, where, in a few minutes, it heats violently and boils. The thick liquid gradually becomes thicker, until it is converted into a solid porous mass; the pores being produced by the bubbles of steam which are driven through it, owing to the heat resulting from the reaction of the ingredients on each other. This porous mass (ALUM-CAKE; CONCENTRATED ALUM) appears perfectly dry, although retaining a large amount of combined water. It also contains all the silica of the original clay, but in such a state of fine division, that the whole appears homogeneous; whilst it imparts a dryness to the touch which can scarcely be given to pure sulphate of alumina. From this substance a solution of pure sulphate of alumina is easily obtainable by lixiviation, and allowing the resulting solution to deposit its silica before using it, but for many purposes the presence of the finely divided silica is not objectionable. The sulphate of alumina solution so obtained is adapted to all the purposes in dyeing for which alum is now employed; the sulphate of potash or of ammonia in the latter being an unnecessary constituent, and one merely added to facilitate the purification and subsequent crystallisation of the salt. To obtain ALUM from the porous alum-cake, the proper proportion of acid having been used in its preparation, or subsequently added, it is only necessary to precipitate its concentrated solution with a strong solution of a salt of potash, or of ammonia, or a mixture of them, and to otherwise proceed as before.

_Ratio._ In the above process the sulphide of iron of the shale or schist is converted by atmospheric oxygen into sulphate of iron and sulphuric acid; the sulphuric acid decomposes the clay, setting silica free, and producing sulphate of aluminum. The sulphate of iron is mostly got rid of by concentrating the solution of the mixed sulphates, and the mother-liquors are converted into alum by the addition of the salt of potassium. When chloride of potassium is used, it yields chloride of iron and sulphate of potassium, the latter combining with the sulphate of aluminum, and the former remaining behind in the mother-liquor. See ALUMS (in Chemistry).

_Comp._ Potassium alum has the formula K_{2}SO_{4}.Al_{2}(SO_{4})_{3}.24Aq.

_c._ From CRYOLITE.

1. (Thomson's method.) Decomposition of cryolite by ignition with carbonate of lime. From the ignited mass the aluminate of soda is obtained by lixiviation with water, and into the solution carbonic acid gas is passed, when there result precipitated hydrated gelatinous alumina and carbonate of soda, which remains in solution. If it be desired to obtain the alumina as an earthy compact precipitate, bicarbonate of soda is used instead of carbonic acid. While the clear liquor is boiled down for the purpose of obtaining carbonate of soda, the precipitated alumina is dissolved in dilute sulphuric acid; this solution is evaporated for the purpose of obtaining sulphate of alumina (the so-called concentrated alum), or the solution after having been treated with a potassa or an ammonia salt is converted into alum.

2. (Sauerwein's method.) Decomposition of cryolite by caustic lime by the wet way. Very finely ground cryolite is boiled with water and lime, the purer the better, and as free from iron as possible, in a leaden pan. The result is the formation of a solution of aluminate of soda, and insoluble fluoride of calcium (lime). When the fluoride of calcium has deposited, the clear liquid is decanted, and the sediment washed, the first wash-water being added to the decanted liquor, and the second and third wash-waters being used instead of pure water at a subsequent operation. In order to separate the alumina from the solution of aluminate of soda, there is added to the liquid while being continuously stirred very finely pulverised cryolite in excess, the result of the decomposition being alumina and fluoride of sodium, (soda). When no more caustic soda can be detected in the liquid, it is left to stand for the purpose of becoming clear. The clarified solution of fluoride of sodium is then drawn off, and the alumina treated as above described. The solution of fluoride of sodium having been boiled with caustic lime yields a caustic soda solution, which having been decanted from the sediment of fluoride of calcium is evaporated to dryness. Recently the fluoride of calcium occurring as a by-product has been used in glass-making.

3. The decomposition of cryolite by sulphuric acid yields sulphate of soda convertible into carbonate by Leblanc's process, and sulphate of alumina free from iron. This method of decomposing cryolite is, however, by no means to be recommended, as owing to the liberation of hydrofluoric acid, peculiarly constructed apparatus are required, whilst the sulphate of soda has to be converted into carbonate.

_d._ From Bauxite. This mineral, occurring in some parts of Southern France, in Calabria, near Belfast, and in other parts of Europe, consists essentially (viz. 60 per cent.) of hydrate of alumina, more or less pure. In order to prepare alums and sulphate of alumina from it, the mineral is first disintegrated by being ignited with carbonate of soda, or with a mixture of sulphate of soda and charcoal; in each case the lixiviation of the ignited mass yields aluminate of soda, from which, by the processes already described under "Cryolite," alum, or sulphate of alumina, and soda are prepared.

_e._ From blast-furnace slag. Lürmann recommends the slag to be decomposed by means of hydrochloric (muriatic) acid. From the resulting solution of chloride of aluminum the alumina is precipitated by carbonate of lime, any dissolved silica being precipitated at the same time. The alumina is dissolved in sulphuric acid, leaving the silica.

_Prop._ Alum crystallises in regular octahedrons, often with truncated edges and angles; (see _engr._); and sometimes in cubes, but only when there is a deficiency of acid in its composition, with the alkali in slight excess of the proper quantity. (Löwel.)[38] It is slightly efflorescent in dry air: soluble in 18 parts of cold water, and in rather less than its own weight of boiling water; tastes sweet, acidulous, and very astringent; is styptic; and reddens litmus. When heated it melts, loses its water of crystallisation, and becomes white and spongy (DRIED ALUM); a strong heat, short of whiteness, decomposes it, with the evolution of oxygen and a mixture of sulphuric and sulphurous anhydride; calcined with carbonaceous matter it suffers decomposition, and furnishes a pyrophoric residuum (HOMBERG'S PYRO'PHORUS). Ignited with alkaline chlorides, hydrochloric acid is liberated; which also occurs when their concentrated solutions are boiled together. Ammonia precipitates pure hydrate of aluminum from potassium alum; but only a subsulphate from the simple sulphate of alumina. Sp. gr. 1·724; but, when containing ammonia, often so low as 1·710.

[Footnote 38: The ordinary alum, of commerce, consisting of large crystalline masses, which do not present any regular geometrical form; but by immersion in water for a few days, octahedral and rectangular forms are developed on its surface. (Daniell.)]

_Tests, &c._ It is easily recognised by its crystalline form, its taste, and by its complete solubility in water. Its aqueous solution gives a white gelatinous precipitate soluble in excess; a platinum wire moistened with the solution imparts a violet colour to the blowpipe flame; and chloride of barium gives a white precipitate insoluble in nitric acid.

_Pur._ When pure, its solution is not darkened by tincture of galls, sulphuretted hydrogen or ferrocyanide of potassium; neither does it give any precipitate with solution of nitrate of silver. Heated with caustic potassa, or quick-lime, it does not evolve fumes of ammonia.

_Adult., &c._ The principal impurity, and one which renders alum unfit for the use of the dyer, is iron. This may be readily detected by the blue precipitate it gives with ferrocyanide of potassium, or the black precipitate with sulphide of ammonium, which are very delicate tests.[39] Lime, another very injurious contamination, may be detected by precipitating the alumina and iron (if any) with ammonia, and then adding oxalate of ammonia to the boiled and filtered liquid. The liquid filtered from the last precipitate (oxalate of lime) may still contain magnesia, which may be detected by the white precipitate caused on the addition of an alkaline phosphate. Common alum frequently contains ammonia, from urine, or the crude sulphate of the gas-works, having been employed in its manufacture. Powdered alum is frequently adulterated with common salt, in which case it gives a white curdy precipitate with nitrate of silver, turning black by exposure to the light.

[Footnote 39: Good English alum contains less than 0·1% of iron. The best Roman or Italian alums seldom contain more than ·005% of iron-alum, notwithstanding their exterior colour.]

_Phys. eff. &c._ In small quantities alum acts as an astringent; in larger doses as an irritant. It acts chemically on the animal tissues and fluids, is absorbed, and has been discovered in the liver, spleen, and urine (Orfila), the last often becoming acid (Kraus). Externally, it is astringent. The almost general use of alum by the English bakers is one of the most fertile sources of dyspepsia and liver and bowel complaints in adults; and of debility and rickets in children. Bad teeth and their early decay is another consequence of the daily use of alum in our food. The bone matter (phosphate of lime) of bread, instead of being assimilated by the system, is either wholly, or in part, converted into a salt of alumina, which is useless and incapable of appropriation. When alum has been taken in poisonous doses an emetic should be given, followed by warm diluents and demulcents, containing a little carbonate of soda; and subsequently by a purgative.