different Earths for Ckrton; 47 



. XX VII. Fifteen grains of pure clay were mixed with J of 

 a grain of carbon, and exposed for an hour to a heat of 165* 

 oi Wedgwood. I found the clay quite unaltered as to co- 

 lour. The charcoal had glazed the interior of the crucible 

 in place of uniting to the pure clay. This led me to infer 

 that the combination of carbon was not in the ratio of the 

 absolute temperature, but in the ratio of the fusibility of 

 the mass. In all these experiments I found that carbon 

 united with S'turbridge clay at an inferior temperature to 

 that at which it combined with Cornwall clay, the fusibility 

 of the former being much greater than that of the latter j 

 and I found it quite impossible to colour pure clay by the 

 most minute particle of carbon. In place of 15 grains, I 

 found the product only weighed 7. Lost 8 grains of water. 



XXVIII. Twenty grains of pure clay were exposed to 

 1 6*6? of Wedgwood, and then found to weigh only 8 grains. 

 This was mixed with 2 grains of pure lime and half a grain 

 of carbon, and an imperfect reduction obtained. The mass 

 was only partially vitrified. 



XXIX. Twenty grains of pure clay and I grains of pure 

 lime were intimately mixed and exposed. The result was a 

 very perfect glass arranged in detached irregular columns 

 or crystals upon the bottom of a Cornwall clay pot. The 

 purity of these masses was entire. The colour generally 

 whitish, but in some places tinged with pale yellow. 



XXX. Twenty grains of pure clay, 5 grains of pure lime, 

 and 1 grain of carbon, were exposed for an hour ; when I 

 obtained a small flat button of earth, hollow in the centre 

 and entirely black upon its upper surface. It, however, con- 

 tained a portion cf the clay and lime, white, and rough as if 

 granulated. In a few places, symptoms of vitrification and 

 glass were evident. The charcoal had disappeared, and the 

 interior of the pot remained unglazed. In point of weight, 

 the whole mass was reduced to a fraction more than ten 

 grains. 



XXXI. Twenty grains of pure clay, 5 grains* of pure 

 lime, and 2 grains of carbon, formed bv fusion a rough 

 half-softened mass of an uniformly black colour. The char- 

 coal was all united to the clay ; but a small portion of the 

 mixture, in a pulverulent form, and of a gray colour, re- 

 mained unfused, which indicated a saturation of the car- 

 bonaceous principle, first manifested in excess by retarding 

 the fusibility of the mixture. 



It would appear from these experiments, that pure clay 

 causes to disappear a quantity of carbonaceous matter equa! 

 to l-10th part of its weight; but as the clay operated upon. 



contained 



