226 GEOLOGY OF OHIO 



ing brick manufacture, for in refractory material the main value of the 

 product depends on the proper mixing and blending of the qualities of 

 the various ingredients. 



Clay prepared by dry pan and tempered by wet pan is in the most 

 satisfactory shape for use that modern experience is able to suggest. 



In some cases as in the manufacture of mill brick from all plastic 

 clays, the use of a pug mill is permissible, because the natural plasticity 

 of the clay and the fact that it is all one kind, render a mere mixing with 

 water sufficient. 



The tempering of the clay being completed, the moulding process 

 begins. 



Fire brick of good quality are still made largely by hand; the aim 

 of the maker is to produce in each brick, an absolutely structureless piece 

 of clay, which can have no tendency to failure of strength by the influence 

 of any machinery in its formation. 



No machinery has yet been devised which enables the production of 

 such an article. The auger and plunging machines are wholly unsuited 

 to the needs of the fire brick maker, each brick is with them but a sec- 

 tion of a bar of clay of very objectionable structure. 



The nearest approximation to good structure is obtained in the soft 

 mud machines and these are sometimes brought into requisition. 



The best fire brick, however, are still hand moulded ; by the human 

 hand each brick becomes a unit by itself and no structural defects are 

 obtained. 



The labor of hand moulding is severe and costly; 4,000 per day is the 

 standard day's work for each moulder and his off bearers, whose work is 

 to take the product to its place on the dry floor, sand the monlds, and 

 bring in the supply of tempered clay. 



Where hand moulding is the only means of manufacture, the mould- 

 ers tables are arranged along one side of the dry floor, a certain space of 

 which is allotted to the product of each table. The work of the day is 

 usually finished by noon and is put on the dry floor as fast as made- 

 Early in the afternoon, the pressing of the brick begins. This is so man. 

 aged as to allow each portion of the day's product about an equal portion 

 of the day to dry before pressing. The press crew consists of four men, 

 who, by use of a portable press, do a similar stint to the moulders, 4,000 

 per day's work. 



This pressing when partly dried is made necessary by the softness of 

 the temper for hand moulding; it would remove some expense if the 

 pressing and moulding could be performed in one continuous operation. 



By this system, bricks are dried in just twenty- four hours; the work 

 of each crew being so timed as to keep always a sufficient space for work 

 between dry brick on their way to the kilns and the new crop being 

 deposited on the floor. 



