BY COMPRESSIOIT, 403 



made, iince it afforded proof of complete fufiorr. The car- 

 bonate had boiled over the lips of the little lube, ftanding, as 

 juft defcribed, with its mouth upwards, and had run down to 

 within half an inch of its lower end : moft of the fubftance was 

 in a frothy ftate, with large round cavities, and a lliining fur- 

 face; in other parts, it was interfperfed with angular malfe*, 

 wliich have evidently been furrounded by a liquid in which they 

 floated. IL was harder, I thought, than marble; giving no 

 etTervefcence, and not turning red like quicklime in nitric 

 acid, which feemed to have no efFe6l upon it in the lump. It 

 was probably a compound of quicklime with the fu'bftance of 

 the tube. 



With the fame barrel repaired, and with others like it, 

 many (imilar experiments were made at this time with great 

 fuccefs ; but to mention them in detail, would amount nearly 

 to a repetition of what has been faid. I Ihall take notice of 

 only four of them, which, when compared together, throw- 

 much light on the theory of thefe operations, and llkevvife 

 feem to eftablifh a very important principle in geology. Thefe 

 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 Account of fome 



April 1803, in one of the large barrels of old fable, with all the experiments at 



above-mentioned arrangements. The heat had rifen, contrary l^JJ^^^^ ^he 



to my intention, to 78° and 79*^. The tubes came out un- carbonate moft 



contaminated with fufible metal, and everything bore the ap- cfned-^ha"' 



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



fifting of pounded chalk, and of a fmall piece of •'"^p-chalk, ^^^^^'^^j^^^'^^^^J^^^^ 



came out clean, and quite looi'e, not having adhered to the lime-ftone and 



inCde of the tube in the fnialleft degree. There was a lofs of of'".a''^'e»,w^'<=^ 



, , I • • r 1 I retained their 



41 percent, and the calcmation leemed to be complete; Ihej-ajbonic acid. 



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



etfervefcence 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 tbewn in 



Fig. 24 and 25), the large tube was filled over the fmall one, 



with various maffes of chalk, fotne 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 



