CLAY WORKING INDTSTRIES. 2bl 



The use of dry press machinery does away with the necessity of the 

 use of any dryer, though as a matter of expediency a tunnel dryer is gen- 

 erally used, and the cost of production is very greatly decreased over the 

 old plan. 



The manufacture of other refractory materials than fire brick is rep- 

 resented at present mainly by the glass pot and glass works supply trade. 

 Retorts for gas making were formerly manufactured at three or four 

 points in the state. The extensive use of iron retorts and the perfection 

 of other gas processes have very seriously crippled this trade in the 

 United States however, and clay retorts are only manufactured at a few 

 points in the count} 7 . 



The manufacture of steel work specialities, like nozzles, stoppers* 

 stopper sleeves, ladle brick, Bessemer tuyeres, etc., is carried on in a lim- 

 ited way in one or two factories. 



Glass pot manufacture is probably the highest and the most tech- 

 nical work in the refractory material business. The service which is ex- 

 acted from a glass pot has probably no equal for severity, unless the work 

 of a steel crucible be considered. 



The pots are of various types and sizes, but a large pot of the cov- 

 ered style weighs thirty-five hundred to four thousand pounds. It not 

 only has to stand up in a furnace filled with flames at a high temperature 

 and sustain its own weight, but must retain a fluid charge of a ton or 

 more of molten glass whose ingredients comprise the most powerful fluxe s 

 like soda ash and oxide of lead. It is a wonder how a pot can be made to 

 last at all, but cases are not infrequent where they are made to last a 

 number of months. They are never allowed to cool when once heated 

 on account of the danger of cracking but are kept continuously in service 

 until worn out. 



The material used in glass pot construction comprises only the finest 

 refractory clays. Ohio furnishes only one or two clays used in this 

 business. 



The Mineral Point clay, which occurs on the Lower Kittanning 

 horizon has been used for this purpose for a number of years. Its 

 quality has been greatly improved by a system of rigorous hand picking 

 and chipping. 



The majority of glass-pot clays come from Germany and Missouri. 

 Every clay now used is subjected to a most rigorous inspection at the 

 mines and at the factory. At the factory this work is performed by 

 women, who break open every lump and by chipping free it from every 

 speck of impurity. No piece larger than a walnut is permitted to enter 

 the mixtures. The mixtures employed are made on the same principal 

 as those compounding in fire brick. The calcine is supplied in part by 

 calcined flint clays, but more largely by old pot shells returned from 

 service. These old shells have to be chipped with the most scrupulous 

 care from the adhering layer of glass inside and the scorified and incrusted 



