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.
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.
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.
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.
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.
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.
CALX aerata (calcareous earth mild), contaminated by a ſmall proportion of magneſia ſalita.
CALX aerata (calcareous earth mild) contaminated by clay.
CALX aerata (calcareous earth mild), contaminated by ſiliceous earth.
CALX aerata (calcareous earth mild), contaminated by clay and ſiliceous earth. (See § 115.)
Cronstedt Min. §§ 25. 28. Calcareous Marle.
CALX aerata (calcareous earth mild), contaminated by iron and manganeſe. Martial.
Cronstedt Min. §30. See alſo §203. Hæmatites.
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.