On the Method of Condensation in Calorimetry. 363 



peated under very different conditions of surface area. It is evident 

 from them that the extent of surface exposed by a substance to the 

 steam affects the result only in a very trifling degree ; the repeated 

 consistency can hardly be the result of chance. As liability to radia- 

 tion errors will increase, caiteris paribus, with extent of surface, they 

 reveal, I think, that the method is not open to appreciable error from 

 such sources. 



Table II illustrates, in the cases of gypsum, calcite, and aragonite, 

 minerals fairly constant in chemical composition, fidelity to the 

 chemical nature of a substance through varying conditions of weight, 

 bulk, shape, and surface texture. 



Table II. 





W. 



w. 



t 



o 



1 • 





Sp. heat. 



Hydrous calcium sulphate. 

















Gypsum : — 

















Clear crystal of selenite .... 



21-048 







•965 



10 



•00 



100 -10 



-27264 



Four clear crystals of selenite 



13 -204 







•b23 



7 



•24 



100-40 



0-27164 



Fibrous silky gypsum .... 



30-150 



1 



•393 



9 



•20 



100-40 



-27167 



Fragments of rough white 



1 31 -547 



1 



•456 



9 



98 



100 -40 



0-27374 



gypsum 















Calcium carbonate — Calcite, 

















rhombohedral : — 

















Iceland spar, limpid crystal. . 



33 -904 



1 



•156 



10 



00 



99-76 



-20383 



Milk-white rhombohedron . . . 



35 -815 



1 



•135 



16 



•75 



b9-9a 



0-20439 



Three slender hexagonal 

 crystals, limpid 



1 10 -044 







•329 



13 



•04 



99 -60 



0-20340 



Group of tapering, clouded 



1 31 -524 



1 



075 



11 



•90 



99-50 



-20908* 















White chalk, in fragments. ... 



22 -454 







•747 



12 



•30 



99 -80 



-20415 



White chalk, fragments from 



| 21 -737 







706 



13 



•77 



99 35 



0-20390 















Calcium carbonate — Aragonite, 

















orthorhombic : — 

















Two yellow transparent erys- 



1 24 -331 







•806 



12 



•45 



99-65 



0-20401 





28-161 







•934 



11 



•60 



99-00 



-20393 



Apart from experiment, I think sufficiently careful consideration 

 shows that we might expect very considerable accuracy from the 

 method. There is theoretically, it will be found, but one source of 

 error needing serious consideration ; it is the danger of precipitation 

 occurring, not on the surface of the substance, but at points close to 



* For a brief notice of such abnormal cases see my paper " On the Specific 

 Heats of Minerals," ' Roy. Soc. Proc.,' vol. 41, p. 250. 



