158 GEOLOGY OF OHIO. 



The end cut bars of clay thus produced are not perfect bars except 

 in outward form ; they are in reality a divided or split bar and the arrange- 

 ment of the particles of clay in various parts of the bar is not alike; this 

 will usually cause the bar to crook or warp in drying. Other objections 

 can be raised against this method of making end cut brick. 



2nd. By changing the auger and auger cases and dies of an end cut 

 machine to a side cut outfit, side cut brick can be produced as well as in a 

 machine especially made for the purpose. If both kinds of brick are 

 needed, the proper thing to do, is to buy an end cut machine of good 

 design and capable of making the desired quantity of end cut brick in a 

 single bar of clay. This machine will then be useful in either capacity, 

 but if a side cut machine be used to make end cut brick it is either at the 

 risk of over-taxing its strength in producing a single stream of clay, or 

 in making an inferior out-put in making two or more streams at once. 



The general characteristics of the bar of clay produced by auger 

 machinery are well marked. To begin with, the bar has the same disposi- 

 tion to defects, due to its passage through a die, which were carefully set 

 forth in treating of the bar produced in plunger machines. 



Aside from this structure, the gathering and assembling of the par- 

 ticles of clay by the constant revolution of a screw unavoidably causes 

 their arrangement around a center point. 



The mere fact of the particles arranging themselves around a center 

 is not detrimental but when the clay is plastic it tends to slip over the 

 polished surface of the auger and the smooth surfaces thus produced do 

 not readily unite again, and as the clay is pushed forward through the die 

 these separate successive waves or layers of clay coming from the auger 

 are readjusted into layers of clay around the center of the bar. Thus the 

 tendency of the auger machine to arrange its clay around a central point 

 becomes a very serious defect in treating a plastic cla}^. With a gritty 

 rough, coarse grained clay this tendency is much reduced, as the clay does 

 not readily form the slips or smooth spots irom contact with the auger. 



This tendency of all auger machines to build the bar of clay out of 

 concentric layers is of course most strongly developed in the end cut ma- 

 chines for there the propelling force is greatest and the molding forces of 

 the die are greatest. Side cut bars while still formed around a center are 

 much less laminated. 



This characteristic fault of the product of the auger mill is something 

 which is inherent in the nature of the machine ; it is not like the fault of 

 the plunger machine which can be partly overcome by the proper appli- 

 ances. All that can be done is to see that the conditions which tend, to 

 produce laminations are obviated just as much as possible. 



The clays which laminate most in auger machninery are rich, fat, 

 aluminous clays, clays whose natural plasticity is great. Clays of this 

 kind cannot be worked in an auger machine with the production of ware 

 which is structural!}" sound. If the clays are gritty, not naturally plastic 



