Part 2

ALKALI _volatile nitratum_ (nitrous ammoniac) is generally found along with common nitre.

§ 52.

ALKALI _volatile ſalitum_ (ſal ammoniac or common ammoniac.) I have examined ſome from Veſuvius, and ſome from the Solfaterra near Naples.

The ſalts hitherto enumerated are perfect neutrals, thoſe which follow are imperfect (§§ 53, 56.)

§ 53.

ALKALI FOSSIL, only in part ſaturated with a peculiar acid is called tinkal; after depuration, borax. It is dug out of the earth in the kingdom of Thibet[25]. Borax takes nearly an equal weight of acid before the alkaline properties entirely diſappear[26].

I believe no one has yet found the acid of borax united either to the vegetable or volatile alkalies.

§ 54.

ALKALI VEGETABILE _aeratum_ (mild vegetable alkaly) is hardly ever found native, unleſs in the neighbourhood of woods deſtroyed by fire.

In the year 1774, at Douai in Flanders, a ſpring was diſcovered ſurrounded by a wall, whoſe waters, beſides other impregnations, contained 11 grains of vegetable alkaly in a pint[27].

§ 55.

ALKALI MINERALE _aeratum_ (mild foſſil alkaly, natron, the nitre of the ancients) is found plentifully in many places, particularly in Africa and Aſia, either concreted into chryſtallized ſtrata, or fallen to a powder; or effloreſcing on old brick walls, or laſtly, diſſolved in ſprings. It frequently originates from decompoſed common ſalt. I am not ignorant that the acid of common ſalt adheres ſtrongly to its baſis ſo as not to be expelled by fire; but perhaps the viciſſitudes of the atmoſphere continually acting for ages, may be more powerful. In immenſe plains covered over with this alkaly, ſcarcely any common ſalt is found upon the ſurface, but the deeper you dig the more it is contaminated by it, the common ſalt being yet undecompoſed for want of acceſs of air.

§ 56.

ALKALI VOLATILE _aeratum_ (mild volatile alkaly) has been found in pump waters in London[28], in Lauchſtadt[29], at Frankfort on the Mayne[30], and copper immerſed therein is ſaid to have been diſſolved into a blue liquor.

The three alkalies mentioned above as ſaturated with aerial acid, differ greatly from cauſtic alkalies, in the mildneſs of their taſte, in their property of chryſtallizing, and in their efferveſcing with acids which expel the aerial acid, but they ſtill change vegetable blues to greens, though not ſo powerfully as the cauſtic alkalies do. Therefore, although the ſubtil aerial acid in other reſpects gives them neutral properties, yet in this it does it but imperfectly.

§ 57.

The compounds of earths and acids which poſſeſs ſolubility mentioned at § 20, are decompoſed and precipitated by mild, but not by phlogiſticated alkalies.

§ 58.

TERRA PONDEROSA _vitriolata_, (heavy ſpar, marmor metallicum, calk) is placed with the earths (§ 89.) Terra ponderoſa _nitrata_ i. e. terra ponderoſa united to the nitrous acid, perhaps exiſts ſomewhere, but has never been met with; neither has the terra ponderoſa united to the _aerial_ acid, yet been found[31]. Terra ponderoſa _ſalita_ i. e. terra ponderoſa with the _muriatic acid_ Mr. HIELM ſays[32] is diſſolved in the waters of the lake Vettern and its neighbourhood.

§ 59.

CALX _vitriolata_ (gypſum, ſelenite) is not only found diſſolved in various waters, but alſo in many places forms immenſe ſtrata. It is placed by all mineralogiſts amongſt the earths, but I think improperly. When burnt it generates heat with water, but in a leſs degree than lime does.

§ 60.

CALX _nitrata_ (nitre of lime; terrene nitre) is ſometimes found in water, but very ſparingly. It is ſaid that the chalk hills in ſome parts of France become ſpontaneouſly impregnated with nitrous acid, which may be waſhed out, and after a certain time they will become impregnated with it again.

§ 61.

CALX _Salita_ (fixed ammoniac) occurs very frequently in waters.

§ 62.

CALX _aerata_ (marble, limeſtone, chalk, ſpar) is very commonly found diſſolved in waters in conſequence of an exceſs of the aerial acid. When it greatly abounds, the water is ſaid to be hard (_cruda_). By boiling, or by evaporation, it depoſits ſtreaks or cruſts of calcareous matter.

Calx aerata is not ſoluble in water without an exceſs of the ſubtil acid, and therefore might properly be referred to the earths (§ 21).

§ 63.

MAGNESIA _vitriolata_ (Epſom ſalt) is not unfrequent in the waters of England, Bohemia, and other countries. This ſalt is preſently decompoſed by lime water, which circumſtance readily diſtinguiſhes it from the alk. min. vitriol. or Glauber’s ſalt.

§ 64.

MAGNESIA _nitrata_ (magneſia and nitrous acid) is uſually found together with nitre.

§ 65.

MAGNESIA _ſalita_ (magneſia and muriatic acid) is found diſſolved in various waters, but plentifully in ſea water, to which it gives a diſagreeable bitterneſs.

§ 66.

MAGNESIA _aerata_ (common magneſia) with an exceſs of aerial acid it becomes ſoluble in cold water, otherwiſe it is ſcarce ſoluble at all, and therefore ſhould be claſſed with the earths. (§ 21.)

§ 67.

ARGILLA _vitriolata_ (alum) is ſometimes ſpontaneouſly generated by the decompoſition of pyrites lodged in clay, or in argillaceous ſchiſtus.

It is found in a ſpring at Steckenitz in Bohemia[33], in Eaſt Bothnia and elſewhere. What is commonly called _plumoſe_ alum is not a ſaline ſubſtance.

ARGILLA (clay) united to the _nitrous_, _muriatic_[34], or aerial acids has not to my knowledge hitherto been found in any waters.

METALLIC SALTS.

§ 68.

The native ſalts belonging to this diviſion, may be diſtinguiſhed by the phlogiſticated alkaly which precipitates them all. The few which have ſaline properties (§ 20.) we ſhall mention here, referring the reſt to the mineralized metals.

§ 69.

CUPRUM _vitriolatum_ (vitriol of copper, blue vitriol) is found in the mines of Herregrund, Fahlune, and others which contain copper pyrites.

§ 70.

FERRUM _vitriolatum_ (vitriol of iron, green vitriol) is formed from the decompoſition of the more common pyrites.

§ 71.

FERRUM _aeratum_ (iron with aerial acid) diſſolved by an exceſs of acid in the lighter chalybeate waters.

FERRUM _nitratum_, and _ſalitum_ (iron with nitrous and muriatic acids) have never yet been found native.

§ 72.

NICCOLUM _vitriolatum_ (vitriol of Nickel) ſometimes exiſts from the decompoſition of ſulphureous ores of Nickel.

§ 73.

ZINCUM _vitriolatum_ (vitriol of zinc, white vitriol) is ſometimes, though rarely, produced By the decompoſition of pſeudogalena, or black Jack, becauſe this ſubſtance does not very readily decompoſe ſpontaneouſly.

§ 74.

[35]MANGANESIUM _ſalitum_ (manganeſe united to muriatic acid) exiſts in ſome waters Mr. HIELM ſays.

Whether manganeſe be ever united to waters like iron, by means of an exceſs of aerial acid, we know not.

TRIPLE SALTS.

§ 75.

The compound ſalts hitherto enumerated are ſuch as are compoſed of two ingredients only; but ſometimes three or more are ſo united as not to be ſeparated by chryſtallization. The vitriols that we are acquainted with are hardly ever pure, and two or three of them ſometimes are joined together.

Sometimes likewiſe it happens that neutral ſalts join earthy ſalts, and earthy ſalts metallic ones. I generally diſtinguiſh compound ſalts according to the number of their principles, whether the ſame acid be joined to ſeveral baſes, or the ſame baſis to different acids; or laſtly, whether ſeveral menſtrua and ſeveral baſes are joined together. Hence ariſe ſalts triple, quadruple, &c. which the diligence of after times muſt illuſtrate. I ſubjoin the moſt remarkable examples of triple and quadruple native ſalts which have occurred to me.

§ 76.

ALKALI MINERALE SALITUM (common ſalt) contaminated by _magneſia ſalita_. The common ſalt when pure does not deliqueſce, but this degree of purity is ſeldom found, and in the native foſſil production (_ſal gem_) never.

§ 77.

MAGNESIA _vitriolata_ (Epſom ſalt) contaminated by _ferrum vitriolatum_[36] (vitriol of iron.)

§ 78.

ARGILLA _vitriolata_ (alum) _native_, contaminated by _vitriol of iron_. In the aluminous ſchiſtus it ſometimes effloreſces in a feathery form. Is this the plumoſe alum of the antients?

§ 78*.

ARGILLA _vitriolata_ (alum) native; contaminated by ſulphur and vitriolic acid.

At the places about Wedneſbury and Bilſton, in Staffordſhire, where the coal pits are on fire, this ſubſtance ſublimes to the ſurface, and may be collected in conſiderable quantity during dry or froſty weather. I cannot be certain that this is a true chemical union, but the eye cannot diſtinguiſh the parts. Perhaps the ſulphur volatilizes the alum and ſo becomes intimately mixed with it. The exceſs of vitriolic acid keeps it in a deliqueſcent ſtate.

I believe a ſimilar compound ſubſtance ſublimes at the Solfaterra near Naples. W.

§ 79.

ARGILLIA _vitriolata_ (alum) native, contaminated by _vitriol of cobalt_. In the mines of Herregrund and Idra this may be ſeen, ſhooting out into long ſlender filaments. Perhaps this is the _trichites_ of the Greeks. Diſſolved in water it immediately betrays the preſence of vitriolic acid, upon the addition of terra ponderoſa ſalita (muriatic acid ſaturated with heavy earth.) By the addition of phlogiſticated alkali a precipitate of cobalt is thrown down, which makes a blue glaſs with borax or microcoſmic ſalt.

§ 80.

CUPRUM _vitriolatum_ (vitriol of copper) contaminated by _iron_.

§ 81.

FERRUM _vitriolatum_ (vitriol of iron) contaminated by _nickel_.

§ 82.

CUPRUM _vitriolatum_ (vitriol of copper) and vitriol of iron contaminated by _zinc_. Such is found at Fahlune.

CLASS II. EARTHS.

§ 83.

Before we can underſtand the nature of earths, we muſt know their component parts. Thoſe earths which cannot be further decompoſed we call _primitive_, and thoſe which conſiſt of two or more of theſe intimately united, _derivative_. By this union we do not mean a mere mechanical diffuſion, at leaſt not ſuch as can be diſtinguiſhed by the eye, as is the caſe in ſtones, (_ſaxa_.)

§ 84.

It is evident that the primitive earths will conſtitute ſo many natural Genera, and different mixtures of theſe the Species.

They who would make ſeveral Genera out of one primitive earth, muſt ſeparate the glaſſy, red, white, horny ſilver ores, and other different compoſitions into as many Genera, or elſe act inconſiſtently with their own principles.

§ 85.

At preſent we only know five primitive earths. They who reckon fewer, reſt their opinions upon fanciful metamorphoſes unſupported by faithful experiments[37]. As experiments teach us that there are five primitive earths, it is evident that the Species ariſing from the mixture of theſe cannot exceed twenty-four, viz. 10 double (conſiſting of two earths) 6 triple, 3 quadruple, and the 5 primitive.

Although theſe different mixtures are poſſible, and probably do exiſt, they have not yet been all found. The natural compoſitions of acids with the earths, forming ſubſtances not ſoluble in 1000 times their weight of boiling water, and which may be called ſaline earths, muſt be added to the ſpecies, as they are certainly chemical combinations.

§ 86.

The primitive earths hitherto detected are,

TERRA PONDEROSA, or heavy earth. CALX, calcareous earth. MAGNESIA, magneſia. ARGILLA, argillaceous earth. TERRA SILICEA, ſiliceous earth.

And we muſt believe theſe to be primitive, until it ſhall appear by proper experiments that they may be ſeparated into others ſtill more ſimple, or changed into one another by art.

Theſe are firſt to be conſidered in their greateſt ſimplicity and purity, although nature never preſents us with ſuch, nor can they even by art be rendered abſolutely free from all heterogeneous mixture. Water and aerial acid readily unite with the four firſt, and when expelled by fire, a little of the matter of heat is added, and remains until driven out by a more powerful attraction. But in this ſtate they poſſeſs a degree of purity not to be attained by any other known method. Therefore it is neceſſary to examine them when ſufficiently burnt in order to diſtinguiſh better what properties depend upon adhering heterogeneous matters.

HEAVY EARTH, OR TERRA PONDEROSA.

§ 87.

To obtain this as pure as poſſible, the ſpathum ponderoſum § 89 (heavy ſpar) muſt be reduced to a fine powder, and with equal parts of fixed alkaly and charcoal duſt roaſted for an hour in a covered crucible. Powder the maſs, and add nitrous or muriatic acid diluted until all efferveſcence ceaſes, and the liquor be ſenſibly acid. To this liquor add mild fixed alkaly, and the heavy earth will be precipitated in a mild ſtate. If the acids or the alkaline ſalt contain any vitriolic acid, the heavy ſpar will immediately be regenerated. What remains undiſſolved by the acid is heavy ſpar, not decompoſed. The proceſs may be repeated upon this, but the product will then contain ſome martial earth and ſome clay from the crucible, therefore the firſt part will be the moſt pure.

§ 88.

TERRA PONDEROSA _aerata_, (heavy earth) has a ſpecific gravity of 3, 773[38]. 100 parts of it contain about 28 of water, 7 of aerial acid, and 65 of pure earth. It efferveſces with acids: with the vitriolic acid forms heavy ſpar, not ſoluble in water; with the nitrous and muriatic acids, it yields chryſtals, not very readily ſoluble; but with the vegetable acid the chryſtals deliqueſce.

When free from all contamination of acid or alkaly it ſcarcely melts in the fire, but loſes ³⁵⁄₁₀₀ of its weight. When united with the matter of heat, (i. e. rendered cauſtic) it diſſolves in 900 times its weight of water; and when this ſolution is expoſed to the atmoſphere, a cream or cruſt ſeparates at the top, which efferveſces with acids. After burning, it unites to acids without efferveſcence; but heat is produced, and the union is more tardy than when it is in a mild ſtate[39].

When cauſtic, it expels the volatile alkaly from ſal ammoniac, and forms a hepar with ſulphur, the watery ſolution of which is but imperfectly decompoſed by the nitrous or muriatic acids, upon account of the remarkable attraction betwixt this earth and the acid of the ſulphur, which it even takes from the vegetable alkaly[40].

When we compare theſe properties with thoſe which belong to common calcareous earth, mentioned at (§§ 92, 93), we ſhall readily ſee wherein they agree, and wherein they differ.

§ 89.

TERRA PONDEROSA _vitriolata_ (heavy ſpar) is full four times as heavy as an equal bulk of water. It diſſolves entirely, though ſparingly, in concentrated boiling vitriolic acid, but the addition of a ſingle drop of water occaſions a precipitation. The ſame thing happens to gypſum; but that requires much leſs acid to diſſolve it, and the precipitation is made more ſlowly. If the heavy ſpar contained any ſulphur, it muſt certainly have appeared when the whole was diſſolved, but I never could find any thing like it.

CRONSTEDT, Min. § 18. 2.

_Marmor metallicum druſicu_ § 19 C. Ponderous Spar.

§ 90.

TERRA PONDEROSA _vitriolata_, impregnated with bitumen, and mixed with gypſum, alum, and ſiliceous earth.

CRONSTEDT Min. § 24. _Lapis hepaticus._ Liver Stone.

A nucleus of this kind, taken out of a piece of alum ore from Andrarum in the province of Skone, yielded, in 100 parts, by analyſis, 33 of ſiliceous earth, 29 of cauſtic heavy earth, earth of alum about 5, and quick-lime from 3 to 7, beſides the water and vitriolic acid. By calculation it appears, that theſe baſes, together with vitriolic acid enough to ſaturate them, ought to weigh 71, which, with the addition of 33, exceeds the amount of the original 100. This increaſe points out the difference of a maſs newly chryſtallized, and of one carefully dried.

§ 91.

When we conſider that the terra ponderoſa was altogether unknown before the year 1774, and that many mineralogiſts are even now unacquainted with it, we cannot wonder that we know ſo few ſpecies of it. I have ſcarce a doubt but the _terra ponderoſa aerata_ may be found mixed with other earths in many ſpecimens, when they come to be examined by chemical means more accurately than they could be heretofore. (See notes to §§ 58 and 88.)

CALCAREOUS EARTH, OR CALX.

§ 92.

As calcareous earth united to the aerial acid is found native, it requires but little trouble to have it pure. Let ſelected pieces of chalk, reduced to fine powder, be repeatedly boiled in pure water: this diſſolves any calx or magneſia ſalita which it may contain. This done, it holds no heterogeneous matter but what mechanically adheres to it, the quantity of which is generally extremely ſmall. If we deſire to be free from this likewiſe, diſſolve the waſhed chalk in diſtilled vinegar, precipitate with volatile alkaly, and after waſhing the precipitate well, dry it.

§ 93.

The ſpecific gravity of calcareous earth thus purified, is 2,720. 100 parts of it contain about 34 of aerial acid, 11 of water, and 55 of pure earth.

Acids unite with it efferveſcing, and a centenary (centenarius) excites about 22 degrees of heat. The vitriolic acid forms gypſum, difficult to diſſolve, (§ 59). The nitrous and muriatic acids form deliqueſcent ſalts (§§ 60, 61), and the acetous acid permanent chryſtals.

Pure calcareous earth does not melt in the fire, but loſes ⁴⁵⁄₁₀₀ of its weight. It diſſolves in 700 times its weight of water, generating heat[41]. Acids diſſolve it, producing from a centenary 252 degrees of heat, but without any efferveſcence. This laſt circumſtance may be beſt obſerved by immerging the burnt earth in water, to diſſipate a part of the heat, which would otherwiſe make the acid boil. The water likewiſe expels the atmoſpheric air from the pores of the lime. In this ſituation, if nitrous or muriatic acid be poured upon it, and if it was previouſly well burnt, no efferveſcence will take place. The ſolution proceeds ſlowly[42], but the ſaturation becomes as perfect as if the calcareous earth had been in a mild ſtate. This burnt earth, or lime, expels the volatile alkaly from ſal ammoniac in a cauſtic ſtate, and it diſſolves ſulphur; but this compound is ſeparated upon the addition of any acid, even the aerial.

§ 94.

Amongſt the native Species of this genus, we muſt firſt mention the CALX _aerata_ (marble, limeſtone, chalk) which conſtitute immenſe ſtrata. Its chief properties are enumerated above (§ 92). It is very rarely found entirely free from iron, which exiſts even in the pureſt Icelandic ſpar, and indeed in almoſt every foſſil production; upon which account only the more remarkable impregnations with iron will be noticed in the following pages.

CRONSTEDT Min. §§ 5–12.

§ 95.

CALX _aerata_ (calcareous earth _mild_), with more or leſs _petroleum_. It efferveſces with acids, and diſſolves; with the vitriolic acid frequently turning brown. Is fœtid when heated or rubbed. The oil is not in ſufficient quantity to be collected, by diſtillation, in drops; it only fouls the inſide of the veſſels, unleſs a very great quantity be operated upon. In an open fire the colour preſently vaniſhes, from the petroleum drying up. It generally contains a portion of martial clay.

CRONSTEDT Min. §§ 22, 23. _Lapis ſuillus._ Fœtid ſtone.

§ 96.

CALX _fluorata_ (calcareous earth and _fluor acid_), when pure, is wholly ſoluble in nitrous and muriatic acids. Expoſed to heat, below ignition, it emits a phosphoreſcent light. Fluor acid, dropped into lime water, precipitates a powder which has all the properties of the calx fluorata. It is ſometimes, but not always, contaminated by a ſmall proportion of ſiliceous earth and muriatic acid.

CRONSTEDT Min. §§ 97–101. _Sparry fluor._ Blue John.

§ 97.

CALX (calcareous earth) ſaturated with a _peculiar acid_, perhaps of a metallic nature (§ 33). In acids, particularly in the muriatic, it aſſumes a remarkable yellow colour, but is not very ſoluble.

CRONSTEDT Min. § 210. Lapis ponderoſus. Tungſten.

§ 98.

CALX _aerata_ (calcareous earth _mild_), contaminated by a ſmall proportion of _magneſia ſalita_.

Magneſia.

§ 99.

CALX _aerata_ (calcareous earth _mild_) contaminated by _clay_.

Argillaceous.

§ 100.

CALX _aerata_ (calcareous earth _mild_), contaminated by _ſiliceous earth_.

Siliceous.

§ 101.

CALX _aerata_ (calcareous earth _mild_), contaminated by _clay_ and _ſiliceous earth_. (See § 115.)

CRONSTEDT Min. §§ 25. 28. Calcareous Marle.

§ 102.

CALX _aerata_ (calcareous earth _mild_), contaminated by _iron_ and _manganeſe_. Martial.

CRONSTEDT Min. §30. See alſo §203. _Hæmatites._

103.

There can be no doubt that the four firſt (§§ 94–97.), if not the laſt (§ 102), are genuine and diſtinct ſpecies; there is ſome difficulty as to the reſt, dependent, perhaps, only upon mechanical mixtures. If the heterogeneous matters can be diſcerned by the eye, we cannot heſitate to refer the ſubſtance to the ſaxa (ſtones); but in theſe the eye cannot diſcern them. Moreover, we know that the earths have a mutual attraction to each other, and form combinations more intimate than mechanical ones. Earth of alum, precipitated by a cauſtic alkali, and thrown into lime water, preſently loſes its pellucid and ſpongy texture, turns white, and condenſes, abſorbing the lime from the water, and forming an union not to be ſeparated but by chemical means.

From theſe conſiderations, I dare not venture to exclude doubtful ſpecies.

We ſay a thing is _contaminated_ by another, when the mixture is of the mechanical kind; but when things are joined by the ſtronger power of attraction, we ſay they are _united_.

MAGNESIA.

§ 104.

Magnesia, called in the diſpenſatories, and by apothecaries _magneſia alba_, is a precipitation from its union with vitriolic acid, called Epſom ſalt. If this earthy precipitate be wanted in the greatest degree of purity, the Epſom ſalt must be taken chryſtallized, and well depurated, diſſolved in distilled water, and precipitated by volatile alkaly. Let the liquor be boiled for a few minutes, in order that what is kept in ſolution by the aerial acid may ſubside.

§ 105.

Magneſia, thus obtained, has a ſpecific gravity of 2,155. 100 parts of it contain about 25 of aerial acid, 30 of water, and 45 of earth[43]. It diſſolves in acids, with a violent efferveſcence, but without heat. It again forms Epſom ſalt, with the vitriolic acid; with the nitrous acid it chryſtallizes, but the chryſtals are deliqueſcent; with the muriatic and vegetable acids it does not chryſtallize, and after drying, greedily attracts moiſture from the atmoſphere.

It does not melt in a moderate heat, but loſes ⁵⁵⁄₁₀₀ of its weight, and then has no attraction for water; diſſolves ſlowly, even in acids, and that without efferveſcence, but with ſome degree of heat. After calcination, it expels the volatile alkaly from ſal ammoniac, and unites to ſulphur, though very feebly.

MAGNESIA _aerata_ (common magneſia) is never found native and unconnected, unleſs in waters, when it is diſſolved by an exceſs of aerial acid. (§ 66.)

§ 106.

MAGNESIA _aerata_ (common magneſia) united with _ſiliceous_ matter. This efferveſces with acids, and not unfrequently ſtrikes fire with ſteel.

§ 107.

MAGNESIA intimately united with _ſiliceous_ matter. The ſoluble part is ſlowly taken up by acids, without efferveſcence.

CRONSTEDT Min. §§79–83. and perhaps § 102–105 alſo; but I have not yet ſubmitted the aſbeſti to the liquid analyſis.

_Soaprock._ _Serpentine._

§ 108.

MAGNESIA united to _argillaceous_, _ſiliceous_, and _pyritical_ matters.

M. MONNET diſcovered this, and the next ſpecies.

§ 109.

MAGNESIA united to _argillaceous_, _ſiliceous_, and _pyritical_ matters, and likewiſe contaminated by petroleum.

This ſpecies reſembles aluminous ſchiſtus, but upon examination is found to contain more magneſia than clay.

§ 110.

All the ſpecies, except the firſt, are more or leſs contaminated by iron, but they do not owe all their colour to this ſubſtance. The green colours altogether vaniſh during ignition, and leave only a white opake maſs.

ARGILLACEOUS EARTH, OR ARGILLA.

§ 111.

By earth of alum (argilla) I do not mean common clay, which is never free from ſiliceous matter, but a pure clay, unmixed, at leaſt, with any other earth. It may be readily obtained by diſſolving Roman or roach alum in diſtilled water, filtering, and precipitating by mild volatile alkaly.

§ 112.

The ſpecific gravity of this pure clay, or earth of alum, is 1,305. It diſſolves in acids, with a little efferveſcence. With the vitriolic acid it forms alum; with the nitrous, muriatic and vegetable acids, deliqueſcent ſalts.