•JA ACTION OF HEAT MODIFIED 



itiHnde(],in or- mcnts, by tlic diminution of its quantity ; it now occured t« 

 t" *" irnrr me, that a susraestion formerly made by Dr. Kennedy, of using 



jiie roiiipicssi- '^^ '^ c ' ^ 1. r w j ' t. 



*vn by its re- water to assist the compressmg torce, might be tollowed with 

 action as advantat^c : That vvliiie sufficient room was allowed for the 

 expansion of the liquid metal, a reacting 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 execution, I have often practised 

 with success. 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 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 

 dropped 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 th« 

 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 sohd mass, before the heat 

 had reached the included moisture. The difficulty was U> 

 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 difficult}', 

 however, by first heating the breech of the barrel, (containing 

 a sufiicient quantity of fusible metal), almost to redness, and 

 then setting it into a vessel full of water, till the temperature 

 had sunk to the proper pitch, which I knew to be the case 

 when the hissing noise produced in the water by the heated 

 barrel ceased ; the cradle, during the last stage of this opera- 

 tion, being held close to the muzzle of the barrel, and ready- 

 to be thrust into it. 

 Sncfcssfiil ex- On the 2d of May, I made my first experiment in this way, 

 using the same air-tube as in the last experiment, which was 

 equal in capacity to one-thirtieth of a cubic inch. Half a 

 grain of water was introduced in the manner just described. 

 'J'he barrel, after an hour of red-heat, was let <lown by a rope 

 and pulley, which I took care to use in all experiments, in 

 which there was any appearance of danger. All was sound. 



The 



pfnment. 

 Tcinp. 24\ 



