of Sir James Hall's Experiments . 217 



No. IS, likewise from pounded chalk, is perfectly fresh and 

 entire, though made more than two years ago; it shows 

 some beautiful clear crystals of spar in parallel plates, but 

 they are so small as to require the use of a glass. 



Nos. 19, 20, 21, show examples of fusion and action on 

 the tubes. In No. 19. a shell is finely united to some 

 pounded chalk. In No. 20. the mass, originally of pounded 

 chalk, is sinking upon itself, and acting at the same time 

 upon the tube; the fracture of the carbonate, in its pure 

 parts, showing brilliant facettes of crystallization. In No. 21, 

 the carbonate in a state like the last, the compound of 

 porcelain and carbonate showing its liquidity by penetrating 

 the tube so as to form a distinct vein of a dark colour, and 

 then spreading on its outside to a considerable extent, ter- 

 minating with the black line alluded to in the account of 

 the experiments. 



Nos. 22, 23, 24, give proofs of entire fusion. In No. 22. 

 we see two porcelain tubes inclosed for preservation in a 

 glass tube : the end attached to the little wooden cup must 

 be held downwards, to show the position in which the expe- 

 riment was made. The innermost porcelain tube stands with 

 its muzzle upwards, and the outermost covers it in the in- 

 verse position. The carbonate was contained in the inner 

 tube: during the action of heat, the barrel failed suddenly, 

 and the carbonate has boiled over the lips of the inner tube, 

 running'dowii, as here appears, almost to its bottom ; thus 

 proving that immediately previous to the failure of the ap- 

 paratus the carbonate had been in a liquid state. 



No. 23, two masses of carbonate welded together in a 

 complete state of froth. The substance shining and semi- 

 transparent. No. 24, two separate masses exposed together 

 to heat; one from pounded chalk, now in a state quite like 

 the last; the other put in as a lump of chalk, dressed flat 

 at both ends, and a letter cut on each end (as done in many 

 of the experiments). It is in a shining and almost trans- 

 parent state; at one end the fiat form and the letter are vi- 

 sible j the other end is completely rounded in fusion, with 

 a glassy surface. 



No. 25. 



