different Earths j or Carbon, 43 



whitish yellow porcelain, which had flown freely upon the 

 bottom of the crucible. 



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

 or l-10th of chalk, were easily reduced into a blackish glass, 

 The surface was shining; the fracture spotted with whitish 

 brown concretions; but the general appearance was a black 

 incompact semi-glass. 



IX. Fifty grains of clay mixed with 3 grains of chalk, to 

 which was added half a grain of carbon, yielded a dense 

 porcelain glass of a dull lead-blue colour. The carbon had 

 totally disappeared. This result, so very different from 

 No. VII, was occasioned simply by the addition of the mi- 

 nute portion of carbon. 



X. Fifty grains of the same clay, mixed with 3 grains of 

 chalk and 1 grain of carbon, yielded a mass half elass 

 and half porcelain. The colour a deep black. The char- 

 coal had entirely disappeared. 



XI. Fifty grains of clay, 3 grains of chalk, and 1J grain 

 of carbon, yielded an unshapely mass, composed of very 

 dark glass, and the mixture in a vitrified gritty state. A 

 quarter of a grain of carbon remained untaken up. 



XII. Fifty grains of vitrified Sturbridge clay pot, finely 

 pounded, was mixed with 5 grains of chalk, and fused into 

 a beautiful red spotted porcelain very much resembling 

 some varieties of porphyry. The surface was more glassy 

 than the fracture, shining, and covered with wavy and cir- 

 cular impressions. The colour was most probably owing to 

 the oxide of iron contained in the chalk. The great differ- 

 ence betwixt this and the result of No. VIII, wherein „the 

 same proportions, but with raw clay, were used, and in 



, which a black glass was obtained, might be owing to the 

 absence of water, which in the former might tend to super- 

 oxygenate the iron. In the latter experiment the vitrified 

 clay could contain little or no water; and if the affinity which 

 clay is generally admitted to have for oxygen was exerted, 

 the iron might in the last experiment be considerably de- 

 oxidated, and give the singular tinge of red to the whole 

 mass. 



XIII. Fifty grains of vitrified clay, 3 grains of chalk, 

 and 1-i grain of carbon, were thoroughly mixed, and sub- 

 jected to a heat similar to the former. The result was a 

 convex button of glass, of a flirty blueish black colour. 

 Upon breaking the mass I found it hollow, and entirely 

 filled with a beautiful arrangement of a mixture of the car- 

 bonaceous matter and the residuum ash. The group was 

 fibrous resembling down, and so extremely light as to ele- 

 vate 



