258 Mr. J. Joly. [Nov. 18, 



The case of aragonite is unexpected. Its specific heat has been 

 obtained by Regnault, Kopp, Neumann, and myself. The experi- 

 ments fall into a,- and /3-groups, having values identical with those of 

 ealcite, and the remarkable fact appears that although the minerals 

 differ in crystalline symmetry and specific gravity, the evidence is in 

 favour of ascribing the same thermal capacities to both. The experi- 

 ments are — 



Sp. h. Sp. gr. Observer. 



r Two transparent crystals (Bohemia) 0-2040 2'955 J. 

 "I „ „ „ (Auvergne) Q'2039 2-955 J. 



[Aragonite 0-2030 — K. 



p „ 0-2085 — R. 



Neumann's result, 0*2018, probably comes under the « variety. A 

 coincidence of error adequate to account for this nearly unanimous 

 agreement between the two forms of ealcite is improbable. The in- 

 ference would appear to be that in both forms the molecules possess 

 nearly equal freedom. From my own results on transparent crystals 

 of both forms the molecular restraint seems perhaps greater in 

 aragonite. This is probable, too, from the phenomena attending the 

 heating of aragonite. The crystals spontaneously break and develope 

 cracks even at the low temperature of the steam ; a phenomenon which, 

 be it observed, probably in some slight degree falsifies the results. 



The sp. h. of a specimen of massive rough barites from Glenda- 

 lough, co. Wicklow, is sufficiently remarkable to justify notice. In 

 this case the nearly pure nature of the specimen was placed beyond 

 doubt by analysis. The sp. h. obtained was — 



Sp. lu Sp. gr. 



Rough crystalline barites .... 0*10316 4*172 



my other observations on this mineral ranging from 0'1092 to 

 0*1117. Neumann records 0*1088 ; Regnault, 0-1128, As the 

 specimen was unaffected by acids, the presence of PbS0 4 was sug- 

 gested as the only likely admixture competent to lower the sp. h. 

 On this account I analysed the substance. The result is — 



BaS0 4 991 



Mn0 2 0-3 



CuFeS 2 0-2 



Pb trace 



Ca . . trace 



Fe 3 3 0-6 



100-2 



The specific gravity, it will be seen y is also abnormal for barites 

 (4-3 — 4'7, Dana). The sp. gr. of the other specimens examined by 



