id Effects of Heat modified by Compression. 



loss of weight, and the compound retaining its fusibility in 

 low heats *. 



In the early part of 1S04, some experiments were made 

 with barrels, which I wished to try, with a view to another 

 series of experiments. The results were too interesting to 

 be passed over ; for, though the carbonic acid in them was 

 far from being completely constrained, they afforded some 

 of the finest examples I had obtained of the fusion of the 

 carbonate and of its union with silex. 



On the 13th of February an experiment was made with 

 pounded ovster-shells, in a heat of 33°, without any water 

 being introduced to assist compression. The loss was ap- 

 parently of 13 per cent. The substance of the shell had 

 evidently been in viscid fusion : it was porous, semi-trans- 

 parent, shining in surface and fracture; in most parts with 

 the gloss of fusion, in many others with facettes of crystal- 

 lization. The little tube had been set with its muzzle up- 

 wards; over it, as usual, lay a fragment of porcelain, and 

 on that a round mass of chalk. At the contact of the porce- 

 lain and the chalk they had run together, and the chalk had 

 been evidently in a very soft state ; for, resting with its weight 

 in the porcelain, this last had been pressed into the sub- 

 stance of the chalk deeper than its own breadth, a rim of 

 chalk being visible without the surface of the porcelain ; just 

 as when the round end of a knife is pressed upon a piece of 

 soil butter. The carbonate had spread very much on the inside 

 of the tube, and had risen round its lip, as some salts risa 

 from their solution in water. In this manner, a small quan- 

 tity of the carbonate bad reached the outer tube, and had 

 adhered to it. The black colour frequently mentioned as 



* Thr retentive power here ascribed to the porcelain tubes, seems not to 

 accord with what was formerly mentioned, of the carbonic acid having been 

 driven through the substance of the tube. But the loss by this means has 

 probably been so sm; 11, that the native properties of the carbonate have not 

 been sensibly changed : or, perhr.ps, this penetrability may not be so uni- 

 versal as I have been induced to think, by having met with it in all the cases 

 which I tried. In this doubt I strenuously recommend a further examination 

 t to gentlemen who have easy access to such porcelains as that 

 of Dresden or of Seve. 



accompanying 



