MODIFIED by COMPRESSION. 117 



four experiments differ from each other only in the heat em- 

 ployed, and in the quantity of air introduced. 



The firft of thefe experiments was made on the 27th of A- 

 pril 1803, in one of the large barrels of old fable, with all the 

 above-mentioned arrangements. The heat had rifen, contrary 

 to my intention, to 78 ° and 79 . The tubes came out un- 

 contaminated with fuhble metal, and every thing bore the ap- 

 pearance of foundnefs. The contents of the little tube, con- 

 lifting of pounded chalk, and of a fmall piece of lump-chalk, 

 came out clean, and quite loofe, not having adhered to the 

 infide of the tube in the fmalleft degree. There was a lofs of 

 41 per cent., and the calcination feemed to be complete ; the 

 fubftance, when thrown into nitric acid, turning red, without 

 effervefcence at firft, though, after lying a few minutes, fome 

 bubbles appeared. According to the method followed in all 

 thefe experiments, and lately defcribed at length, (and fliewn 

 in fig. 24. & 25.), the large tube was filled over the fmall one, 

 with various mattes of chalk, fome in lump, and fome rammed 

 into it in powder ; and in the cradle there lay fome pieces of 

 chalk, filling up the fpace, fo that in the cradle there was a 

 continued chain of carbonate of four or five inches in length. 

 The fubftance was found to be lefs and lefs calcined, the more 

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

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

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

 in the heart, furrounded and intermixed with quicklime, dif- 

 tinguifhed by its dull white. In nitric acid, this fubftance be- 

 came red, but efFervefced pretty brifkly; the effervefcence 

 continuing till the whole was diflblved. The next portion 

 of chalk, was in a firm ftate of limeftone ; and a lump of 

 chalk in the cradle, was equal in perfection to any marble 

 I have obtained by compreffion : the two iaft-mentioned pieces 

 of chalk erTervefcing with violence in the acid, and fhewing 



no 



