1821.] Dr. Clarke on Arragonite. 61 



which caused it, as a carbonate of lime, to be confounded with 

 common calcareous or oriental alabaster. Its chemical and 

 mineralogical characters are all of them those of arragonite ; and 

 it possesses the discriminative marks which have been before 

 stated as proofs of the identity of this mineral. It dissolves 

 with vehement effervescence in pure muriatic acid, without 

 leaving any insoluble residue. When sulphuric acid is added 

 to the solution, a disengagement of the muriatic acid imme- 

 diately ensues, and the residue is a sulphate, which, as it 

 is not wholly soluble in dilute muriatic acid, and from other 

 trials,* seems to contain sulphate of strontia ; but this requires 

 further examination. Its specific gravity is 2*7. The specific 

 gravity of the arragonite stalactites of Antiparos varies in the 

 different specimens from 2*9 to 2*7 and 2*6, the difference 

 wholly depending upon the degree of crystallization which the 

 mineral has experienced. When the crystallization is perfect, 

 the specific gravity amounts to 2*9, because those stalactites in 

 which an incipient crystallization only is discernible, are of a 

 more porous nature ; the same degree of density does not take 

 place in the mineral, air being admitted and held between the 

 different fibres and layers. For this reason, the specific gravity 

 of the solid hexagonal crystals of arragonite from Arragon equals 

 always 2 - 9; but the arragonite of the Quantock Hills Cavern, in 

 Somersetshire,"!" is exactly 2*71, as estimated both by our present 

 Professor of Chemistry, the Rev. I. Cumming, and by myself; 

 thereby agreeing with the specific gravity of the arragonite of the 

 Theban Soros, discovered by Mr. Belzoni. The specific gravity also 

 of the common coralloidal arragonite, or Jios fern, deserves to 

 be noticed ; because no account of it has yet been published ; 

 which made me the more desirous of making the experiment. 

 For this purpose I selected a specimen from the mines of Styria, 

 weighing 682-j^ths grains. By immersion in pump water, the 

 weight lost amounted to 250-/g-ths. 



Consequently its specific gravity being 2*725 strikingly corre- 

 sponds with the specific gravity of the arragonite from the 

 Somersetshire cavern, and also with that of the remarkable Soros 

 which has given rise to the preceding observations. 



From all, therefore, that has been now adduced, it is plain that 

 the same specific gravity does not apply to all the sub-varieties of 

 this remarkable mineral ; but that its specific gravity may be 

 greater or- less as crystallization is more or less advanced. Some 



* The insoluble sulphate, after being exposed to the action of dilute muriatic acid for 

 the solution of the sulphate of lime, was exposed to a red heat in a plaiinum crucible, 

 and again placed in dilute muriatic acid. It was then calcined at a very high tempera« 

 ture, and found to be soluble in distilled water ; but being exposed to atmospheric air, a white 

 pellicle was speedily formed upon the surface which fell to the bottom, another and 

 another pellicle succeeding, until the whole sJbstance in solution was precipitated. This 

 precipitate tinged the flame of burning alcohol of a purple hue, and was, therefore, 

 believed to be carbonate of strontian. 



•f About Beven miles from Bridgewater. 



