154 GEOLOGY OF OHIO. 



are now used for producing end cut bricks and paving blocks — that is 

 from 2x4 to 4x5. In either larger or smaller sizes the tendency- 

 diminishes. 



The effect of this tendency has an important bearing on the structure 

 of the bar of clay. If made of clay which is a little too dry in temper 

 it will break into pieces showing on one side of the fracture a cup-shaped 

 cavity, and on the other a conical projection. If the temper be a little 

 soft, the corners of the bar will tear back or ruffle up, making an utterly 

 unsaleable article If the clay be tempered well, but too little plastic in 

 its nature, the corners of the bar will show a multitude of cracks going 

 down into the clay for quite a distance and trending forward at an angle 

 toward the center instead of at right angles to the flow. If the clay 

 be too plastic, the center is liable to flow so much more freely that 

 division lines are formed between the outside and the center and these 

 slipped surfaces or laminations can not be made to unite again, by any 

 subsequent repressing, and naturally these cracks or laminations are a 

 detriment to the strength of the burnt brick. 



These various phenomena which have been mentioned are all due to 

 the one general cause — the flow of the plastic clay through the die and 

 they are faults which are inherent in the case, and not the result of the 

 kind of machine used, or rather of the way in which the pressure which 

 causes the flow is applied. 



Besides these faults, which are common to all, plunger machines are 

 likely to have another which is characteristic of them only — that is the 

 imprisonment of air in greater or less quantity in the substance of the 

 clay from which it cannot escape. 



The pressing chamber is filled with a mass of more or less granular 

 clay at the beginning of each stroke. The motion of the piston forward 

 rapidly consolidates the mass and the air has only the chance to escape 

 by the leakage of the piston head or through the die with the clay. 

 Vents on the surface of the chamber serve but small useful purpose, as 

 they speedily choke with clay and only drain the space close to them. 

 As the air goes out with the clay through the die it generally occupies 

 the space between the slipped or laminated surfaces and thus assists in 

 keeping them apart. Sometimes large cavities are formed and if the clay is 

 too soft it sometimes swells up like a loaf of bread from imprisoned air. 



There is no way yet devised which does away with the introduction 

 of air in bricks from a plunger machine. As would be expected the 

 more granular and sandy the clay is, the less the trouble amounts to, but 

 the limit of sandiness will be attained before the trouble is cured. 



One of the most promising attempts to do away with the trouble has 

 been made by Mr. H. B. Camp at Cuyahoga Falls. He uses a packer 

 which by constant strokes catches and consolidates the soft granular clay 

 from the tempering machinery into a large round bar, this is cut off in 

 chunks or crumbs of seventy-five to one hundred pounds weight and is 



