io6 EFFECTS of HEAT: 



part of the cradle, the remaining fpace being rilled with two 

 pieces of chalk, cut for the purpofe ', the uppermofl 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 guefled 

 to be about 30 ° . After the barrel had flood during a few minutes 

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

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

 siderable force. The lowermofl piece of chalk had fcarcely 

 been acted upon by heat. The upper part of the other piece was 

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

 bonate, in the little tube, had fhrunk very much during the 

 firft action of heat, and had begun to {ink upon itfelf, by a fur- 

 ther advancement towards liquefaction. The mafs was divi- 

 ded 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 fucceflive portions. In 

 feveral places, particularly at the top, the carbonate was very 

 porous, and full of decided air-holes, which could not have 

 been formed but in a foft fubftance ; the globular form and 

 mining furface of all thefe cavities, clearly indicating fu- 

 fion. The fubflance was femitranfparent ; in fome places yel- 

 low, and in fome colourlefs. When broken, the folid parts 

 mewed a faline fracture, compofed of innumerable facettes. 

 The carbonate adhered, from end to end, to the tube, and in- 

 corporated with it, fo as to render it impoflible to afcertain 

 what lofs had been fuftained. In general, the line of contact was 

 of a brown colour ; yet there was no room for fufpecting the 

 prefence of any foreign matter, except, perhaps, from the iron- 

 rod which was ufed in ramming down the chalk. But, in fubfe- 

 quent experiments, I have obferved the fame brown or black 

 colour at the union of the carbonate with the porcelain tubes, 

 where the powder had been purpofely rammed with a piece of 



wood ; 



