^ Effects of Heat modified hy Compression. 



irregularly. On the ledge of the cup, formed by the ends 

 of the foldod platina, were several globular drops like mi- 

 nute pearls, visible to the naked eye, the number of which 

 amounted to sixteen. These seem to have been formed by 

 the entire fusion of what carbonate happened to lie on the 

 ledge, or had been entangled amongst the extremities of the 

 folds, drawing itself together, and uniting in drops, as we 

 see when any substance melts under the blowpipe. This 

 result is preserved entire, without deranging the tube. I 

 am sorry to find that it has begun to fall to decay, in con- 

 sequence, no doubt, of too great a loss of its carbonic acid. 

 But the globules do not seem as yet to have suffered any in- 

 jury. 



April 25. — The same spar was used with two grains of 

 water, and a heat of 33°. I have reason to suspect, how- 

 ever, that in this, and several other experiments made at 

 this time, the metal into which the cradle was plunged, on 

 first introduction into the barrel, had been too hot, so as to 

 drive oft* the water. There was a loss of 6*4 per cent. The 

 result lay in the cup without any appearance of frothing or 

 swelling. The surface was of a clean white, but rough, 

 having in one corner a space shining like glass. The cup 

 being unwrapt, the substance was obtained sound and en- 

 tire: where it had moulded itself on the platina, it had a 

 small degree of lustre, with the irregular semi-transparency 

 of saline marble ; when broken, it preserved that character 

 more, completely than in any result hitherto obtained, the 

 fracture being very irregular and angular, and shining with 

 facettcs in various directions. I much regret that this beau- 

 tiful specimen no longer exists, having crumbled entirely to 

 pieces, notwithstanding all the care 1 took to inclose it with 

 glass and wax. 



April 26. — An experiment was made with some carbo- 

 nate of lime, purified by my friend sir George Mackenzie. 

 Two grains of .vater were introduced, but were lost, I sus- 

 pect, as in the last case. The heat applied was 32°. The 

 loss of weight was 10'C per cent. Yet, though made but 

 one day after the last-mentioned specimen, it remains as 

 fresh and entire as at first, and promises to continue un- 

 changed. 



