[ io ] 



III. Account of a Series of Experiments, showing the Effects 

 of Compression in modifying the Action of Heat. By Sir 

 JAMES Hall, Bart. F.R.S. Land, and Edin. 



■[Continued from our last volume, p. 307.] 



V. Experiments in which Water was employed to increase 

 the Elasticity of the included Air. — Cases of complete 

 Compression. — General Observations. — Soma Experiments 

 affording interesting Results ; in particular, showing a 

 mutual Action between Silex and the Carbonate of Lime. 



r inding that such benefit arose from the increase of elas- 

 ticity given to the included air in the last-mentioned experi- 

 ments by the diminution of its quantity, it now occurred to 

 me, that a suggestion formerly made by Dr. Kennedy, of 

 using water to assist the compressing force, might he fol- 

 lowed with advantage ; that, while sufficient room was al- 

 lowed for the expansion of the. liquid metal, a re-acting 

 force, of any required amount, might thus be applied to the 

 carbonate. In this view I adopted the following mode, 

 which, though attended with considerable difficulty in ex- 

 ecution, I have often practised with succef-s. The weight 

 of water required to be introduced into the barrel was added 

 to a small piece of chalk or baked clay, previously weighed. 

 The piece was then dropoed into a tube of porcelain of about 

 an inch in depth, and covered with pounded chalk, which 

 was firmly rammed upon it. The tube was then placed in 

 the cradle along with the subject of experiment, and the 

 whole was plunged into the fusible metal, previously poured 

 into the barrel, and heated so as merely to render it liquid. 

 The metal being thus suddenly cooled, the tube was encased 

 in a solid mass before the heat had reached the included 

 moisture. The difficulty was to catch the fusible metal at 

 the proper temperature ; for when it was so hot as not to 

 fix in a few seconds, by the contact of the cradle and its 

 contents, the water was heard to bubble through the metal' 

 and escape. I overcame this difficulty, however, by first 

 heating the breech of the barrel (containing a sufficient 

 quantity of fusible metal) almost to redness, and then set- 

 1 ting 



