Effects of Heat modified hy Compression. 17 



accompanying the union of the carbonates with the porce- 

 lain, is here very remarkable. 



On the 26th of February I made an experiment, in which 

 the carbonate was not weighed, and no foreign substance 

 was introduced to assist the compression. The temperature 

 was 46°. The pyrometer had been affected by the contact 

 of a piece of chalk, with which it had united; and some of 

 the carbonate must have penetrated the substance of the py- 

 rometer, since this last had visibly yielded to pressure, as 

 appeared by a swelling near the contact. I observed in 

 these experiments that the carbonate had a powerful action 

 on the tubes of Cornish clay, more than on the pounded 

 silex. Perhaps it has a peculiar affinity for argil, and this 

 may lead to important consequences. The chalk had visibly 

 first shrunk upon itself, so as to be detached from- the sides, 

 and had then begun to run by successive portions, so as still 

 to leave a pillar in the middle, very irregularly worn away; 

 indicating a successive liquefaction, like that of ice, not the 

 yielding of a mass softening all at once. 



On the 28th of February I made an experiment with 

 oyster-shell unweighed, finely ground, and passed through 

 the closest sieves. The pyrometer gave 40°. The piece of 

 chalk below it had been so soft, as to sink to the depth of 

 half an inch into the mouth of the iron air-tube, taking its 

 impression completely. A small part of this lump was con- 

 taminated with iron, but the rest was in a fine state. The 

 tube had a rent in it, through which the carbonate, united 

 with the matter of the tube, had flowed in two or three 

 places. The shell had shrunk upon itself, so as to stand 

 detached from the sides, and bore very strong marks of 

 fusion. The external surface was quite smooth, and shining 

 like an enamel. The internal part consisted of a mixture of 

 large bubbles and solid parts : the inside of the bubbles had 

 a hibtre much superior to that of the outside, and equal to 

 that of glass. The general mass was semi-transparent ; but 

 small parts were visible by the lens, which were completely 

 transparent and colourless. In several places this smooth 

 surface had crystallized, so as to present brilliant facettes, 

 Steadily shining in certain aspect-. I observed one of tin ie 



Vol. 25. No. y;. June ISoG. B faceitca 



