18 Effects of Heat modified by Cdmpression. 



facettes on the inside of an air-bubble, in which it inter- 

 rupted the spherical form as if the little sphere had been 

 pressed inwards at that spot, by the contact of a plane sur- 

 face. In some chalk near the mouth of the large tube, 

 which lay upon a stratum of silex, another very interesting 

 circumstance occurred. Connected with its lower end, a 

 substance was visible, which had undoubtedly resulted irom 

 the union of the carbonate with the silex. This substance 

 was white and semi-transparent, and bore the appearance 

 of chalcedony. The mass of chalk, having attached itself 

 to that above it, had shrunk upwards, leaving an interval 

 between it and the silex, and carrying some of the compound 

 up with it. From thence this last had been in the act of 

 dropping in a viscid state of fusion, as evidently appeared 

 when the specimen was entire, having a stalactite and sta- 

 lagmite corresponding accurately to each other. Unluckily 

 I broke off the stalactite, but the stalagmite continues en- 

 tire, in the form of a little coue. This new substance effer- 

 vesced in acid, but not briskly. I watched its entire solu- 

 tion : a set of light clouds remained undissolved, and pro- 

 bably some jelly was formed ; for I observed that a series of 

 air-bubbles remained in the form of the fragment, and moved 

 together without any visible connection ; thus seeming to 

 indicate a chemical union between the silex and the carbo- 

 nate. The shell, fused in the experiment, dissolved entirely 

 in the acid, with violent effervescence. 



In the three last experiments, and in several others made 

 at the same time, the carbonate had not been weighed j but 

 no water being introduced to assist the compression, it is 

 probable there was much loss by internal calcination; and 

 owing doubtless to this the carbonates have crumbled al- 

 most entirely to dust, while the compounds which they had 

 formed with silex remain entire. 



On the 13th of March I made a similar experiment, in 

 which, besides some pounded oyster-shell, I introduced a 

 mixture of chalk, with 10 per cent, of silex intermixed, and 

 ground together in a mortar with water, in a state of cream, 

 and then well dried. The contents of the tube when opened 

 were discharged with such violence that the tube was broken 



to 



