226 



MELTING POTS 



clay ; burned-clay cement ; coke-powder ; pipe-clay. The pasty mass must be 

 compressed in moulds. The Hessian crucibles from Great Almerode and Epterode 

 are made from a fire-clay which contains a little iron, but no lime ; it is incorporated 

 with siliceous sand. The dough is compressed in a mould, dried and strongly kilned. 

 They stand saline and leaden fluxes in assaying operations very well ; are rather 

 porous on account of the coarseness of the sand, but are thereby less apt to crack 

 from sudden heating or cooling. They molt under the fusing-point of bar-iron. 

 Beaufay in Paris has lately succeeded in making a tolerable imitation of the Hessian 

 crucibles with a fire-clay found near Namur in the Ardennes. 



Berthier has published the following elaborate analyses of several kinds of 

 crucibles : 



Wurzur states the composition of the sand and clay in the Hessian crucibles 

 as follows : 



Clay ; silica 10-1 ; alumina 65-4 ; oxides of iron and manganese 1-2 ; lime 0'3 ; water 23 

 Sand; 95'6; 2-1; 1-5; 0-8 



The composition of some of the best varieties of fire-clay, as deduced from the 

 analyses of Berthier and Salvetat, is given in the following table : 



Quoted from Knapp's ' Technology.' 



Mr. C. Cowper has analysed the clays used at Birmingham for glass-pots. His re- 

 sults were as follow : 



Black-lead crucibles are made of two parts of graphite and one of fire-clay, mixed 

 with water into a paste, pressed in moulds, and well dried, but not baked hard in the 



1 This crucible had beon analysed before being baked in the kiln 



