MAGNESIA.
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.
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.)
MAGNESIA aerata (common magneſia) united with ſiliceous matter. This efferveſces with acids, and not unfrequently ſtrikes fire with ſteel.
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.
MAGNESIA united to argillaceous, ſiliceous, and pyritical matters.
M. Monnet diſcovered this, and the next ſpecies.
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.
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.
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.
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.
When dry, it abſorbs water greedily, becomes ſoft, and, with a due quantity of water, gains ſuch a tenacity, that it may be moulded at pleaſure. This maſs contracts greatly in the fire, from whence ariſe numerous cracks; and with a due degree of heat, it becomes hard enough to ſtrike fire with ſteel. By this burning it loſes its glutinous tenacity, and the water is excluded by the approach of the particles; nor does it again aſſume its former properties, but by ſolution and precipitation.
It may be diſſolved in the dry way, by means of fixed alkaline ſalt, as well as in the liquid way, by acids. The vitriolic acid is better than the others for this purpoſe, becauſe more eaſily concentrated.
Earth of alum neither diſſolves ſulphur, nor decompoſes ſal ammoniac.
ARGILLA (argillaceous earth) united to ſiliceous matter only.
Cronstedt Min. §78. Argilla porcellana. Porcelain clay.
Pipe clay.
I never examined any clay which did not contain a large quantity of ſiliceous earth; generally more than half its weight[[44]].
ARGILLA (argillaceous earth) united to ſiliceous and irony matter.
Cronstedt Min. §§ 87 and 90. Bole. Dye-earth.
Clay.
ARGILLA (argillaceous earth) united to ſiliceous and calcareous matter.
Cronstedt Min. §25. Marga argillacea. Marle.
ARGILLA (argillaceous earth) united to ſiliceous earth and magneſia.
Cronstedt Min. §§ 84, 4. B. Terra lemnia.
Its component parts reſemble thoſe of talc, but differ in their proportions, and are alſo leſs intimately united.
ARGILLA (argillaceous earth) united to ſiliceous, calcareous, and magneſia earths.
Lithomarga.([[45]]) Cronstedt Min. § 84. A.
Stone marrow.
ARGILLA (argillaceous earth) contaminated by vegetable alkaly and ſulphur, or at leaſt by the acid of ſulphur.
Cronstedt Min. § 124. 2. b. Minera aluminis romani.
Alum ore.
It certainly contains vitriolic acid[[46]], and perhaps, alſo, a ſmall portion of ſulphur. The vegetable alkaly ſufficiently ſhews its volcanic origin.
ARGILLA (argillaceous earth) contaminated by ſiliceous matter, pyrites, and petroleum.
Cronstedt Min. § 124. 2. c. Schiſtus aluminaris[[47]].
Alum ſlate.
ARGILLA (argillaceous earth) intimately united with leſs than half its weight of ſiliceous earth, and a ſmall quantity of mild calcareous earth.
Cronſtedt Min. §§ 43–48. Gemma.
The Gems ſuffer no change under the blowpipe, with foſſil fixed alkaly, but are diſſolved by microcoſmic ſalt and borax.
| To this head belong | Rubinus, the | ruby; |
| Saphirus, | ſapphire; | |
| Topazius, | topaz; | |
| Smaragdus, | emerald. |
The tourmaline holds a kind of middle place betwixt the gems and the ſcherle. The colour, in all of them, is owing to iron.
ARGILLA (argillaceous earth) intimately united to half its weight of ſiliceous earth (or more), and a little mild calcareous earth. Scherle.
Cronſtedt Min. §§ 68–71. Granatus et Baſaltes, which I call Scherle.
The remote varieties of theſe are eaſily diſtinguiſhed, the near ones difficultly.
ARGILLA (argillaceous earth) looſely united to half its weight, or more, of ſiliceous earth, and a little calcareous earth.
Cronstedt Min. §§ 108–112. Zeolithus. Zeolite.
There is a great affinity betwixt this and Scherle; but in the zeolite, the component parts cohere ſo looſely, that acids attach and ſeparate them without their being previouſly treated with alkalies; but this is not the caſe with the ſcherles.
Zeolite, contaminated by magneſia, I have not yet examined.
ARGILLA (argillaceous earth) intimately united to a large proportion of ſiliceous earth, and a ſmall proportion of magneſia.
Cronstedt Min. §§ 93–96. Mica. Talcum. [[48]]Glimmer. Talc.
SILICEOUS EARTH,
OR
TERRA SILICEA.
This, like the other primitive earths, is ſeldom found pure. In order to have it ſo, reduce clear quartz chryſtals into powder; melt it with four times the weight of fixed alkaly; diſſolve the whole in water; precipitate by a large quantity of ſtrong acid; carefully waſh and dry the precipitate.
The acid muſt be uſed in a ſuperfluous quantity, that any other earths contained may be diſſolved.
The ſpecific gravity of this earth, is 1,975. The particles, when firſt precipitated, occupy, in water, at leaſt twelve times the ſpace that they do when dried; ſo that, when ſufficiently fine, they may remain ſuſpended therein; nay, when vehemently heated in a cloſe veſſel, they may be diſſolved. No acid, except that of fluor ſpar (§ 30) has any action upon this earth. Fixed alkalies unite with it in the liquid way, but in the dry way they ſeize it with great vehemence, and convert twice their weight of it into a permanent transparent glaſs. Such is its affinity to alkalies, that it imparts to clay, which is always loaded with it, the power of ſeparating ſome of the acid from nitre and common ſalt. When pure, it is refractory in the fire.
Although ſiliceous earth is not altogether ſimple, yet, in mineralogy, it muſt be conſidered as primitive, until deciſive experiments ſhew us from which of the preceding earths it is derived[[49]].
TERRA SILICEA (ſiliceous earth) united to very ſmall quantities of calcareous and argillaceous earth.
Cronstedt Min. § 51. Quartzum. Quartz.
TERRA SILICEA (ſiliceous earth) united to argillaceous earth.
Cronstedt Min. § 58. Calcedonius. Chalcedony.
And perhaps the Opal. The Hydrophanus is only a variety of theſe.
Whether the carnelian, and other ſiliceæ, of finer or coarſer texture, belong to this or the preceding ſpecies I cannot yet determine with certainty.
TERRA SILICEA (ſiliceous earth), united to an argillaceous and highly martial earth.
Cronstedt Min. §§ 64, 65. Jaſpis. Jaſper.
TERRA SILICEA (ſiliceous earth), loaded with martial earth.
Martial.
Cronstedt Min. § 53.
This ſpecies is often called jaſper, but improperly, becauſe it contains no argillaceous earth.
TERRA SILICEA (ſiliceous earth), united to argillaceous and a ſmall quantity of calcareous earth.
Cronstedt Min. § 63. Petroſilex. Chert.
TERRA SILICEA (ſiliceous earth) united to argillaceous earth and a little magneſia.
Cronstedt Min. §66. Feldſpathum. Feld ſpat.
TERRA SILICEA (ſiliceous earth), united to magneſia, mild calcareous earth, fluor ſpar and alſo to the calxes of copper and iron. Chryſopraſius. I have not examined this, but inſert it upon the experiments of Mr. Achard.
To determine accurately the ſpecies of earths is the moſt difficult part of mineralogy, for innumerable analyſes yet remain to be made. But that which now ſeems intricate and obſcure will become plain and eaſy when experiments have been ſufficiently multiplied.
CLASS III.
INFLAMMABLES,
OR
BITUMINA.
To this head we refer all foſſils containing phlogiſton in ſuch great abundance, that under proper management they are inflammable. The Genera are obviouſly very few, and accurately ſpeaking there is only one Genus. But ſince phlogiſton is so very ſubtle as not by itſelf to become the object of our ſenſes, it will perhaps be adviſeable to conſider its more ſimple combinations as Genera: this has long been done ſo far as reſpects the metals, by univerſal conſent.