2IQ ACTIOK OF HEAT MOCIFIES 



many others with facettcs of crystallization. The little tube 

 had been set with its muziilc upwards ; over it, as usual, lay 

 a fragment of porcelain, and on that a round mass of chalk. 

 At the contact of the porcelain and the chalk, they had run 

 together, and the chalk had been evidently in a very soft state ; 

 for, resting with its weiglit on the porcelain, this last had been 

 pressed into the substance 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 soft butler. The carbonate had spread very 

 much on the inside of the tube, and had risen round its lip, as 

 some salts rise from their solution in water. In this manner, a 

 small quantity of the carbonate had reached the outer tube, 

 and had adhered to it. The bl&ck colour frequently m.ention- 

 ed as accompanying the union of the carbonates with the por- 

 celain, is here very remarkable. 

 Similar expcri- 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 pyrome- 

 ter, since this last had visibly yielded to pressure, as appeared 

 by a swelling near the contact. I observed in these experi- 

 ments, 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 mas^often- 

 ing all at once. 

 Bimilarexpcri- On the 28th of February, I made an experiment with oy- 

 ofappearances, s'^^-i'-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 contaminated with 

 iron, but the rest was xn a fine stale. The tube had a rent in 



it, 



