ioo EFFECTS of HEAT 



by which the laft could be counteracted ; but I faw no remedy 

 for the firft. I began, therefore, to defpair of ultimate fuccefs 

 with tubes of porcelain *. 



Another circumflance confirmed me in this opinion. I 

 found it impracticable to apply a heat above 27 ° to thefe tubes, 

 when charged as above with carbonate, without deftroying them, 

 either by explolion, by the formation of a minute rent, or by 

 the actual fwelling of the tube. Sometimes this fwelling took 

 place to the amount of doubling the internal diameter, and 

 yet the porcelain held tight, the carbonate fuftaining but a 

 very fmall lofs. This ductility of the porcelain in a low 

 heat is a curious fad, and fhews what a range of temperature 

 is embraced by the gradual tranfition of fome fubflances from 

 a folid to a liquid ftate : For the fame porcelain, which is 

 thus fufceptible of being ftretched out without breaking in a 

 heat of 2 7 , ftands the heat of 152 °, without injury, when ex- 

 pofed to no violence, the angles of its fracture remaining fharp 

 and entire. 



IV. 



* I am neverthelefs of opinion, that, in fome foliations, experiments with com- 

 preffion may be carried on with great eafe and advantage in fuch tubes. I allude 

 to the fituation of the geologifts of France and Germany, who may eafily procure, 

 from their own manufactories, tubes of a quality far fuperior to any thing made 

 for fale in this country. 



