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MEIGS ON THE RELATION OF 



If sulphur be melted and allowed to solidify at 230° F., it assumes the form of an 

 oblique rhombic prism ; if it be made to crystallize from its solution in bisulphuret of 

 carbon or oil of turpentine, at a temperature under 100°, it appears in the shape of 

 octohedrons with rhombic bases. According to Graham, the crystals of sulphur 

 produced at the higher of two temperatures, become opaque when kept for some days 

 in the air, and pass spontaneously into the other form, in consequence of a new 

 arrangement of atoms ; at the same time their transparency is destroyed, because a 

 mass of crystalline particles takes the place of one crystal, thus causing the light to 

 be refracted in various directions. The crystals produced at the lower temperature 

 are disintegrated and changed into the other form by a moderate heat. 



As in the case of carbon, the varieties of sulphur differ in atomic heat.* 



If chloride of calcium and carbonate of ammonia be mixed together, and the solution 

 brought to a temperature of 50° F., the precipitating carbonate of lime will take the 

 form of rhombohedric crystals, as in calc-spar; if the solution be kept at 150% the 

 crystals appear as cubes, as in arragonite. If these cubic crystals are allowed to 

 remain in the liquid, while the latter is gradually cooling, they are slowly but com- 

 pletely converted into calc spar.f 



According to Fownes, green sulphate of iron crystallizes in two different forms, and 

 with two different proportions of water, according to the temperature at which the 

 salt separates from the solution.J 



A prism of arragonite, exposed to the flame of a spirit-lamp, decrepitates at a low 

 red heat, and breaks up into numerous minute rhombic grains of calc spar. Melted 

 chalk, on cooling into marble, exhibits a rhombohedral structure. From these facts 

 it appears, that while a low temperature gives to CaO, C0 2 the form of calc-spar, a 

 higher temperature is necessary to produce arragonite, — which latter is indeed formed 

 only between very narrow thermometric limits. Below are the atomic heats of 

 different varieties of carbonate of lime. 



CaO, C0 2 

 Calc-spar, 

 Artificial, 

 Arragonite, 

 Iceland spar, 

 Chalk, . 

 Statuary marble, 



Atomic Heat. 

 10.0747 

 10.2515 

 10.3575 

 10.5343 

 10.8474 

 10.8979 



Carbonate of strontia precipitates in an indeterminate form, when chloride of stron- 

 tium is decomposed by carbonate of ammonia in the cold. "When heated, it takes the 

 form of arragonite. But the chlorides of barium and lead, when mixed with carbo- 

 nate of ammonia in the cold, respectively precipitate PbO, C0 2 and BaO, C0 2 in the 



*Regnault. Op. cit., pp. 206, 207. fRose. Philosoph. Mag., 3d ser., vol. xii. p. 465. 



X Elements of Chemistry, p. 176. 



