394f ACTION OF HEAT MODIFIED 



Bxpcnment. On the 2Sth of February, I introduced feme carbonate, ac^ 



Carbonate partly curately weighed, into a fmal! porcelain tube, placed within a 

 part deprived of '^''g^'" One, the reft of the large tube being filled with pounded 

 carbonic acid, chalk ; thefe carbonates, together with Ibme pieces of chalk, 

 placed along with the large tube in the cradle, weighing in 

 all 195.7 grains. On opening the barrel, air ruflied out with 

 a long-continued biffing noife. The contents of the little tube 

 w-ere loft by the intrufion of fome borax which had been in- 

 troduced over the filex, in order to exclude the fufible metal. 

 But the reft of the carbonate, contained in the large tube, came 

 out in a fine flate, being porous and frothy throughout ; fpark.» 

 ling every where with facetts, (he angular form of which 

 was diftinguifhable in fome of the cavities by help of a 

 lens : in fome parts the fubftance exhibited the rounding of 

 fufion ; in many it was in a high degree tranfparent. It was 

 yellow towards the lower end, and at the other almoft colour- 

 lefs. At the upper end, the carbonate feemed to have utiiled 

 with the tube, and at the plates of contrad to have fpread up- 

 on it; the union having the appearance of a mutual a<5tion. 

 The general mafs of carbonate efFervefced rn acid violently, 

 but the thin ftratum immediately contiguous to the tube, 

 feebly, if at all. 

 Similar cxperi- On the 3d of March, I introduced into a very clean tube of 

 rnenr, in which porcelain 36.8 of chalk. The tube was placed in the upper 

 exhibited more P^""*^ ^^ ^'^^ cradle, the remaining fpace being filled vyith two 

 remarkable pieces of clialk, cut for the purpofe ; the uppermoft of thefe 

 ^" *^' being excavated, fo as to anfwer the purpofe of an air-tube. 



The pieces thus added, were computed to weigh about 300 

 grains. There was no pyrometer ufed ; but the heat was guefied 

 to be about 30**. After the barrel had ftood duringa few minutes 

 in its delivering pofition, the whole lead with the rod and 

 cradle, were thrown out with a fmart report, and with con- 

 fiderable force. The lowermoft piece of chalk had fcarcely 

 been a6!ed upon by heat. The upper part of the other piece was 

 in a ftale of marble, with fome remarkable facettes. The car- 

 bonate, in the little tube, bad fiirunk very much during the 

 firft a6tion of heat, and had begun to fink upon itfelf, by a fur- 

 ther advancement towards liquefaction. The mafs was di- 

 vided into feveral cylinders, lying confufedly upon each other; 

 this divifion arifing from the manner in which the pounded 

 chalk was rammed into the tube in fuccefTive portions. In 



feveral 



