128 EFFECT'S of HEAt 



upon a piece of foft butter. The carbonate had fpread very 

 much on the infide of the tube, and had rifen round its lip, as 

 fome falts rife from their folution in water. In this manner, 

 a fmall quantity of the carbonate had reached the outer tube, 

 and had adhered to it. The black colour frequently mention- 

 ed as accompanying the union of the carbonates with the 

 porcelain, is here very remarkable. 



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

 the carbonate was not weighed, and no foreign fubftance 

 was introduced to affift the compreffion. The temperature 

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

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

 the carbonate muft have penetrated the fubftance of the py- 

 rometer, fince this laft had vifibly yielded to preffirre, as ap- 

 peared by a fwelling near the contact. I obferved in thefe ex- 

 periments, that the carbonate had a powerful action on the 

 tubes of Corniih clay, more than on the pounded lilex. Per- 

 haps it has a peculiar affinity for argil, and this may lead to 

 important confequences. The chalk had vifibly firft fhrunk 

 upon itfelf, fo as to be detached from the fides, and had then 

 begun to run by fucceflive portions, fo as ftill to leave a pil- 

 lar in the middle, very irregularly worn away ; indicating 

 a fucceflive liquefaction, like that of ice, not the yielding of 

 a mafs foftening all at once. 



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

 oyfter-fhell unweighed, finely ground, and paffed through the 

 clofeft fieves. The pyrometer gave 40°. The piece of chalk 

 below it had been fo foft, as to fink to the depth of half an 

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

 completely. A fmall part of this lump was contaminated 

 with iron, but the reft was in a fine ftate. The tube had a 

 rent in it, through which the carbonate, united with the mat- 

 ter of the tube, had flowed in two or three places. The 



fhell 



