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.