ON THE THERMAL CONDUCTIVITIES OF CERTAIN ROCKS. 



139 



The specific gravity as well as the specific heat of the specimen of 

 English alabaster proves it (as moistening it with an acid also shows) not 

 to be " oriental alabaster," or calcic carbonate, but calcic sulphate, or a semi- 

 crystalline and compact form of a hydrate of that substance which appears 



Substance 



Coke (of anthra- 

 cite) 



Coal 



Burnt Clay 



White marble... 



Grey marble ... 

 White chalk ... 



Silica (quartz) 



Sodic chloride... 

 Iron pyrites . . . 



Galena. 



Calcic Sulphate, 

 anhydrous . . . 



Calcic Fluoride 



Authority 



Regnault 



Crawford 



Gladolin 

 Regnault 



Specific Heat by 



weight 



0-201 



0-278 



0-185 

 0-216 



0-210 

 0-215 



0-191 



0-214 

 0-130 



O051 

 0197 



Observed 

 1878 



I 



{ 



0-193 

 0-287 



0-374 



0188 

 0-210 



0-221 



0-215 

 0-280 



f 0.187 



\ 0-195 

 0192 

 0-126 



[ 0-084 



| 0-046 

 f 0284 



I O260 

 0-200 



Description of rock, and number 

 of specimens tested (1878) 



Gas-coke (1 specimen). 

 Cannel-coal (3 specimens). 

 /Newcastle house coal (1 speci- 

 J_ men). 

 Brick and firebrick (4 specimens). 

 White Sicilian and Italian mar- 

 bles (2 specimens). 

 Other marbles (7 specimens). 

 " Godstone 



}, chalk „ 



about ' j Pure white f 2s P eCimenS 



chalk 

 Opaqiie white quartz (3 ~| white 

 specimens). >sand 



Quartzite (2 specimens) J - 200 

 Bocksalt (1 specimen). 

 Iron pyrites (1 specimen), 

 f Galena (with 28i p. c. of quartz) ; 

 \. 1 specimen. 



/Galena (with 28^ p. c. of quartz ; 

 I. corrected for quartz). 

 English alabaster (1 specimen). 



/ Plaster of Paris (1 specimen, de- 

 \ ducting half the poss. cor.) 

 Fluor-spar (1 specimen). 



to agree in the property of its specific heat sensibly with plaster of Paris, 

 although not with anhydrous calcic sulphate, to which Regnault assigns a 



much lower specific heat by weight. These properties of minerals, like 

 their specific gravities, certainly form very valuable and easily deter- 



