MODIFIED by COMPRESSION* 89 



III. 



Experiments made in 'tubes of Porcelain. — tubes of Wedgwood* s Ware. 

 — Methods ufed to confine the Carbonic Acid, and to clofe the Pores of 

 the Porcelain in a Horizontal Apparatus. — Tubes made with a view 

 to thefe Experiments. — The Vertical Apparatus adopted. — View of 

 Refults obtained, both in Iron and Porcelain. — The Formation of Lime- 

 flone and Marble. — Inquiry into the Caufe of the partial Calcinations, 

 — Tubes of Porcelain weighed previous to breaking. — Experiments with 

 Porcelain Tubes proved to be limited. 



While I was carrying on the above-mentioned experiments 1 , 

 I was occafionally occupied with another fet, in tubes of por- 

 celain. So much, indeed, was I prepoJTefTed in favour of this 

 laft mode, that I laid gun-barrels afide, and adhered to it du- 

 ring more than a year. The methods followed with this fub- 

 (lance, differ widely from thofe already defcribed, though 

 founded on the fame general principles. 



I procured from Mr Wedgwood's manufactory at Etruria, 

 in Staffordfhire, a fet of tubes for this purpofe, formed of the 

 fame fubftance with the white mortars, in common ufe, made 

 there.. Thefe tubes were fourteen inches long, with a bore 

 of half an inch diameter, and thicknefs of 0.23 being clofed 

 at one end (figs. 9, 10, n, 12, 13.) 



I proposed to ram the carbonate of lime into the breech 

 (Fig. 9. A) j then filling the tube to within a fmall diflance of 

 its muzzle with pounded flint (B), to fill that remainder (C) 

 with common borax of the fhops (borat of foda) previoufly re* 

 duced to glafs, and then pounded ; to apply heat to the muzzle 

 alone, fo as to convert that borax into folid glafs ; then, re- 

 versing the operation, to keep the muzzle cold, and apply the 

 requifite heat to the carbonate lodged in the breech. 



Vol. VI.— P.I. M J 



