404 ACTION OF HEAT W»DIF1ED. 



it was removed from the breech of the barrel, where the heat 

 was grealeft. A fmall piece of chalk, placed at the diftance 

 of hall an inch from the fmall tube, had fome faline fubftance 

 in the iiearf, (urrounded and nitermixed with quicklime, dif- 

 tingui(hed by its dull white. In nitric acid, this fubftance be- 

 came red, but cfFerveroed pretty btilkiv; the effervefcence 

 continuing till the whole was ditfolved. The n«xt portion 

 of chalk was in a firm flale of limeftone; and a lump of 

 chalk in the cradle, was equal in perfcdlion to any marble I 

 have obtained by compreffion : the two laft-mentioned pieces 

 of chalk effervefcing with violence in the acid, and fliewing 

 no rednefs when thrown into it. Thefe (acts clearly prove, 

 that the calcination of the contents of the fmall tube had been 

 internal, owing to the violent heat which had feparated its 

 acid from the moft lieated part of the carbonate, according 

 to (he theory already ftated. The foundnefs of the barrel was 

 proved by the complete ftale of thofe carbonates which lay 

 in lefs heated parts. The air-tube in this experiment had a 

 capacity of 0.29, nearly one.third of a cubic inch. 

 Another expe- The fecond of thele experiments was made on the 29th of 



nment in which April, in the fame barrel wi(h the UR, after it had afFordeci 



the banelfajledi r i /■ i -t^, • , ■ • i • i 



lome good relults. The air-tube was reduced to one-third 



of its former bulk, that is, to one-tenth of a cubic inch.—* 

 The beat rofe to 60''. The barrel was covered externally 

 with a black fpongy fubHance, the conftant indication of fai- 

 lure, and a fmall drop of white rnetal made its appearance. 

 The cradle was removed without any explofion or hiffing. 

 The carbonates were entirely calcined. The barrel had yield- 

 ed, but had refitted well at firft; for the contents of the little 

 tube were found in a complete flate of froth, and running 

 with the porcelain. 

 Third experi- The third experiment was made on the 30lh of April, in 

 ment, very thin another fimilar barrel. Every circumliance was the fame as 

 in the two laft experiments, only that the air-tube was now 

 reduced to half its laft bulk, that is, to one-twentieth of a cu- 

 bic inch. A pyrometer was placed at each end of the large 

 tube. The uppermoCi gave 41*'> the other only 15". The 

 contents of the inner tube had loft 16 per cent, and were re- 

 duced to a moft beautiful (late of froth, not very much injured 

 by the internal calcination and indicating a thinner ftate of 

 fufion than bad appeared. 



3 The 



