MODIFIED by COMPRESSION. 105 



nate, carefully weighed, in the fame barrel with a large quanti- 

 ty of that fubflance ; and by arranging matters fo that the fmall 

 fiducial part mould undergo a moderate heat, while a ftronger 

 heat, capable of producing internal calcination, mould be ap- 

 plied to the reft of the carbonate. In this manner, I made 

 many experiments, and obtained remits which feemed to con- 

 firm this reafoning, and which were often very fatisfactory, 

 though the heat did not always exert its greateft force where I 

 intended it to do fo. 



On the 28th of February, I introduced fome carbonate, ac- 

 curately weighed, into a fmall porcelain tube, placed within a 

 larger one, the reft of the large tube being filled with pounded 

 chalk ; thefe carbonates, together with fome pieces of chalk, 

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

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

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

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

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

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

 out in a fine ftate, being porous and frothy throughout -, fpark- 

 ling every where with facettes, the 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 j 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 united 

 with the tube, and at the places of contact to have fpread up- 

 on it \ the union having the appearance of a mutual a&ion. 

 The general mafs of carbonate efFervefced in acid violently, 

 but the thin ftratum immediately contiguous to the tube, fee- 

 bly, if at all. 



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

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



Vol. VI. —P. I. O part 



