44 On t/ie Affinities of 



vate itself upon the slightest motion given to the glass. The 

 quantity of carbon thus obtained weighed short of I -8th of 

 a grain. Upon examining the fracture of the glass I found 

 its colour darken as it approached the cell where the char- 

 coal was found, and neither so dense nor perfect as towards 

 the surface or extremities of the mass. 



It will appear, therefore, conclusive from these experi- 

 ments, that carbon unites to Sturbridge clay either by ce- 

 mentation or fusion, and the quantities will be to the dif- 

 ferent states of the clay respectively as follows : 



Raw Sturbridge clay in cementation causes to disap- 

 pear 2-J per cent, of carbon, and is thereby changed from 

 a pale straw to a blackish blue colour. Experiments No. I, 

 II, III, and IV. 



Raw Sturbridge clay, fused by the assistance of chalk, 

 causes to disappear 2-£ per cent, of carbon, and thereby 

 changes its colour from a yellowish porcelain to a hetero- 

 geneous mass of black glass and gritty vitrified clay. Expe- 

 riments No. VII, VIII, IX, X, and XL 



But as this clay was found to contain from 18 to 20 per 

 cent, of water, it was probable that part of the carbon would 

 be carried off by the water in the act of evaporation. 



Vitrified clay was used, and a portion of charcoal disap- 

 peared in contact with it equal to 2-J- per cent., changing 

 the colour from a kind of blood red to a blackish blue co«r 

 lour. Experiments No. XII and XIII. 



XIV. One of Wedgwood's rolls, weighing 27 grains, was 

 heated to 163°, and then weighed 20 grains. It was x then 

 put into a crucible filled with charcoal, and exposed for two 

 hours to a stronger degree of heat. It was then found to 

 weigh 187-J grains. Its surface was entirely glazed, of a 

 blackish blue colour. Its fracture presented a small ring 

 of the same colour, proceeding from the circumference of 

 the roll. The interior was pure white. The colour in no 

 place exceeded the limits of the circle. 



XV. A portion of very pure Cornwall clay was exposed 

 in a crucible made of the same stuff, and, after a heat of 

 1 7 1° of Wedgwood, I found the clay loosely connected toge- 

 ther, gritty, and easily pulverized. I returned it with a por- 

 tion of carbon, and gave it the whole "power of the furnace 

 for half an hour. The result was a pulverulent mass of 

 grayish gritty clay, in which the whole of the charcoal em- 

 ployed had disappeared. 



XVI. Twenty grains of pure Cornwall clay, 11 grains of 

 water, and 2 grains of lamp carbon, were formed into a 

 small ball, which was dried, and afterwards exposed to a 



high 



