

46 On the Affinities of 



.a very perfect dark lead-blue glass. The carbon had en> 

 tirely disappeared. 



XXIV. The same proportions of vitrified Cornwall clay 

 and chalk, were exposed in the furnace, intimately mixed 

 with 1-J grain of carbon. The result was a mass of very 

 fine porcelain minutely porous, of a dull blackish lead co- 

 lour. No remains of carbon were visible. 



XXV. Fifty grains of the same clay, mixed with 5 grains 

 of chalk and 2 grains of carbon, were fused into a spongy 

 mass of very black porcelain, somewhat tinged with blue. 

 A few flakes of carbon were found upon the surface of the 

 product, mixed with some snowy white flowers supposed 

 to have come from the residuum ash of the carbon. As 

 soon as the cover was broken from the crucible they began 

 to elevate themselves, and float lightly about. 



The same experiments were performed with a fifth in 

 place of a tenth part of chalk to clay ; and similar results, 

 but more fusible products, obtained. One deduction only, 

 different from the others, I was able decidedly to make,-r~ 

 that the addition of from l-50th to l-100dth part of carbon, 

 when a fifth of chalk was used, increased the fusibility of 

 the mixture from 168° to 152° of Wedgwood. 



It appears therefore generally conclusive, that carbon 

 unites to Cornwall clay either in cementation (see Experi- 

 ments No. XIV, XV, and XVI,) or in fusion, and probably 

 in a much greater proportion, changing the colour of the 

 products from milky white, through various shades of lead 

 blues, to black : increasing the fusibility with small por- 

 tions, and changing porcelain to glass : then again retard- 

 ing the fusibility when an extra quantity is used, and de- 

 stroying the perfection of the glass, and producing a spongy 

 porcelain. The greatest quantity united,' or which disap- 

 peared in the experiments with raw clay, amounted to 1£ 

 grains to 50 of clay, or 3-J- per cent., No. XXI. But as 

 .Cornwall clay contains nearly 15 parts of water in 100, vi- 

 trified clay was used, and the experiments with it indicated 

 an absorption of carbon equal to 4 grains in the 100, or 

 1- J5th part the weight of the clay No. XXV. 



XXVI. A portion of pure clay was taken, and, after being 

 introduced into a crucible made of Cornwall clay, was ex- 

 posed for an hour to the greatest heat of a furnace 8 inches 

 square, with a chimney 48 feet in height. The crucible was 

 found considerably furrowed on the sides, but quite erect. 

 The clay remained pure and unchanged, but much reduced 

 in bulk. It, however, possessed a roughness and asperity 

 .which it had not before its introduction. 



XXVII. 



