24 Effects of Heat modified lij Compression. 



The last experiment was repeated on the same day, and 

 prepared in the same manner, with large fragments of shell, 

 and the point of the periwinkle standing up in the cup. 

 A heat of 34° was applied ; a loss took place of 13° per cent. 

 All the original form had disappeared, the carbonate lying 

 in the cup as a complete liquid, with a concave surface, 

 which did not shine, but was studded all over with the white 

 sphericles or tufts, like those seen in the former results, 

 without anv spice between them. When detached from 

 the cup, the surface moulded on the platina was white and 

 pearly, with a slight gloss. The mass was quite solid, no 

 vestige whatever appearing of the original form of the frag- 

 ments (fig. 33). A small piece, broken off near the apex of 

 the eone, showed the internal structure to be quite saline. 

 In the act of arranging the specimen on its stand, another 

 piece came off in a new direction, which presented to view 

 the most perfect crystalline arrangement : the shining plane 

 extended across the whole specimen, and was more than the 

 tenth of an inch in all directions. Tin's fracture, likewise, 

 showed the entire internal solidity of the mass. Unfortu- 

 nately, this specimen has suffered much by the same decay 

 to which all of them are subject which have lost any con- 

 siderable weight. The part next the outward surface alone 

 remains entire. I have never been able to explain, in a sa- 

 tisfactory manner, this difference of durability, the last- 

 mentioned result having lost more in proportion to its 

 weight than this. 



About the beginning of June I received from Mr. Hat- 

 chett some pure carbonate of lime, which he was so good 

 as to prepare, with a view to my experiments; and I have 

 been constantly employed with it till within these few days. 



Mv first experiments with this substance were peculiarly 

 unfortunate, and it seemed to be less easily acted upon than 

 any substance of the kind I had tried. Its extreme purity, 

 no doubt, contributed much to this, though another cir- 

 cumstance had likewise bad some effect. The powder, 

 owing to a crystallization which had taken place on its pre- 

 cipitation, was very coarse, and little susceptible of close 

 ramming ; the particles, therefore, had less advantage than 



when 



