. qfCalc Spar and Arragonite. 471 



the form of arragonite, possessed a higher specific gravity 

 than calc spar, and therefore occupied a smaller space than 

 the hitter. AUhough this opinion has from that time been 

 pretty commonly admitted, it has never yet been strictly 

 proved, and on this account I found it necessary to make a 

 few experiments with respect to it. For this purpose I heated 

 some crystalline fragments of arragonite from Bilin : after 

 having previously weighed them, 1 weighed again the fallen 

 powder in order to convince myself that no carbonic acid had 

 escaped, and now took the specific gravity of the powder. 

 I always found it as follows in three different experiments, 

 which were always performed with different quantities : 2*703, 

 2*704, and 2*709. In the latter experiment the powder had 

 previously been boiled for some time. According to this, 

 therefore, we may suppose with certainty that arragonite at a 

 weak red heat changes into calc spar; for even if the num- 

 bers found are somewhat lower than those obtained when the 

 specific gravity of small crystals of calc spar is taken, this 

 without any doubt has its cause in the above-mentioned cir- 

 cumstance. 



The disintegration of arragonite at a low red heat is very 

 visible in large crystals, and is a very remarkable phseno- 

 menon ; it occurs, however, only in large crystals, never in 

 small ones or fibrous masses. The Sprudelstein of Karlsbad 

 loses its transparency on being heated, but does not disinte- 

 grate; nor do those small arragonite crystals disintegrate 

 which are found upon the branches of the coralloidal arrago- 

 nite {Eisenbluthe) from Steiermark, nor the microscopic cry- 

 stals of the arragonite artificially prepared. 



If we examine the powder obtained by the disintegration 

 of the larger crystals of arragonite, under the microscope, it 

 has the appearance of quite irregular fragments which are 

 perfectly transparent, but full of cracks and rents. The mi- 

 nute crystals of the coralloidal arragonite from Steiermark 

 retain with their transparency their form also ; they appear, 

 however, in the interior full of rents, and have on their sides 

 cracks often very wide*. The larger only of the microscopic 

 crystals of the artificially prepared arragonite have some rents ; 

 the smaller do not appear at all changed, and possess the same 



* For this reason therefore it would be better to perform the heating in 

 a glass tube blown out at the rriddle into a globe, and during the heating 

 to pass some carbonic acid over the arragonite. In order to be assured 

 whether at the heating of the arragonite any portion of the mass had be- 

 come caustic, it is not sufficient after the addition of some water to see 

 whether the red litmus paper turns blue ; for undecomposed carbonate 

 pf lime always produces the same effect if it be powdered and immersed 

 in water. 



