different Earths for Carhon, 45 



high heat. I found the ball vitrified throughout, and pos- 

 sessed of an uniform black fracture, slightly porous from 

 the excessive heat. A fragment of raw clay, weighing \5 

 grains, was placed at a little distance from the ball in the 

 same pot. It was found perfectly vitrified and glazed, in ' 

 the same manner as the roll in Experiment XIV. The co- 

 loration had penetrated a considerable way further towards 

 the centre of the piece than in the case of the roll, probably 

 owing to the spongy texture of this clay in its native state. 

 The ball weighed, after being exposed, 17 grains ; being five 

 less than the weight of the clay and carbon. The mass of 

 clay 18} grains^ being 2£ less thari when introduced. The 

 quantity of water in the clay being nearly 15 per cent. 



XVII. Fifty grains of raw Cornwall clay were mixed 

 with 5 grains of chalk, and fused into a button of beautiful 

 white porcelain. The colour of the fracture was uniformly 

 pure throughout. 



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

 of chalk and half a grain of lamp carbon, formed by fusion 

 a very perfect glass of considerable density. The colour 

 was light lead-blue, and possessed considerable transparency. 



XIX. Fifty grains of Cornwall clay, 5 grains of chalk, 

 and I grain of carbon, afforded by fusion a glass of a darker 

 colour than the former, but not so perfect, arising from an 

 apparent extra dose of carbon* The charcoal, however, 

 had disappeared, and from the increased colour of the glass 

 its combination was obvious. 



XX. Fifty grains of Cornwall clay, 5 grains of chalk, 

 and li. grain of carbon, yielded a porous mass of porcelain 

 of a very dark rusty black colour. The whole of the carbon 

 disappeared. 



XXI. The same experiment repeated with the addition 

 of half a grain, or in all 2 grains of carbon. The result 

 was a semi-fused mass of vitrified matter, the fracture of 

 which resembled porcelain. The colour was darker than in 

 No. XX, and * grain of carbon remained untaken up. 



XXII. Cornwall clay, vitrified in 168° of Wedgwood: 

 50 grains of this, finely pounded, were mixed with 5 grains 

 of chalk, and fused into a primrose-coloured porcelain glass. 

 This result differs as much from No. XVII, wherein the 

 same proportion of mixture was used with raw clay, as 

 No. XII did from No. VII, in the experiments with Stur- 

 bridge clay. The latter contained from 1 8 to 20 per cent. 

 of water, the former about 15. 



XXIII. Cornwall clay, vitrified, 50 grains, mixed with 

 5 grains of chalk and 1 grain of carbon, yielded by fusion 



« very 



