THE POTTER'S ART. 



this brickwork small holes, ra ra, are left, through which the oven- 

 man from time to time takes out trial-pieces, which are pieces of 

 clay of known quality, and which indicate by the effect produced 

 upon them the progress which the baking has made. When the 

 appearance of these trial-pieces shows that the firing has been 

 sufficiently continued, the furnace and ashpit doors and the 

 damper t are closed, and the oven, with its charge, is left to cool 

 gradually for twenty-four or thirty hours. It is not necessary to 

 delay the withdrawing of the pieces from the oven until they 

 have become quite cold ; but the sudden alteration of temperature 

 would occasion them to crack if they were taken out while their 

 heat was greatly above that of the atmosphere. 



Some potters are occasionally tempted, when the furnace contains 

 articles of small value, to risk the damage here mentioned, and to 

 withdraw the saggers with their contents without delay, their object 

 being to profit by the heat of the furnace either for introducing a new 

 charge, or for drying a fresh set of saggers. No one, however, would 

 be so improvident as to expose the finer descriptions of porcelain to 

 this hazard, in order to gain any such immaterial advantage. 



From the similarity of its appearance to well-baked ship bread, 

 the ware is now called biscuit. Its permeability to water when in 

 this state fits it for being employed in cooling liquids. If pre- 

 viously soaked in water, the gradual evaporation from its surface by 

 means of the air, causes an absorption of heat from the surrounding 

 atmosphere, which is again supplied by neighbouring objects, 

 until an equilibrium of temperature is restored. 



9. As there are no excise or other regulations affecting the manu- 

 facture of earthenware, there are no official documents or records 

 by which the actual extent of the manufacture can be ascertained 

 with precision ; but it is estimated that at the Potteries alone the 

 value of the earthenware produced annually is about 1,700000Z., 

 and that the value of the manufactures of Worcester, Derby, and 

 other parts of the country, may amount to about 750000Z., making 

 a total annual value of 2,4500002. 



The value of the gold consumed annually at the Potteries in the 

 ornamentation of porcelain is 36400Z., and, since about half that 

 amount is consumed in the other seats of the manufacture, it may 

 be stated that the total value of the gold used annually in England 

 in this manufacture is about 54600Z. 



The quantity of coals consumed annually at the Potteries is 

 468000 tons, and, about half that amount being consumed in 

 other factories, it may be stated at about 700000 tons an 

 amount equal to what is consumed in working all the railways of 

 the United Kingdom.* 



* See Lardner's Railway Economy, p. 83. 

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