CELLS AND MANOMETER ATTACHMENTS. 



11 



ran 



escape of water makes further compression of the clay possible. When 

 no more water can be forced out, the press is transferred to its place in 

 Figure 2. The amount of weight to be applied and the duration of the 

 period of pressing are judged entirely by previous observations on the 

 fitness of the products for cutting purposes. In general, the weight 

 employed is that which will give a calculated pressure of 20 tons upon 

 each square inch of the surface of the clay cylinder after an allowance of 

 one-third for loss by friction. The first descent of the weight (53 feet) 

 is usually accomplished in about 2 hours and the second in about 16 

 hours. Ordinarily the pressing is discontinued at the end of the second 

 excursion of the weight. Equivalent results can be secured by lighter 

 weights and longer pressing or by heavier weights and shorter pressing. 

 The object to be attained is, of course, that condition of the clay which 

 will enable one to cut a perfect cell from the pressed cylinder, and for 

 this purpose the clay must be neither too wet nor too dry. 



When the cylinder is to be removed, the press is again placed in the 

 vise, the upper cap (Figure 1 A) is removed and an additional disk is 

 introduced. On replacing the upper cap 

 and removing the lower one, and giving 

 the plunger (Figure 1 A, 4) a slight turn, 

 the cylinder is effectively released, and — 

 owing to the tapered form of the barrel 

 (Figure 1 A) — uninjured. The form of 

 the cylinder is shown in Figure 3 A . 



THE CUTTING OF THE CELLS. 



One of the commoner forms of the 

 finished cell as it is turned out of the 

 cylinder (Figure 3 A) is shown in Figure 

 3 B. Other forms will be represented 

 when the attachment of the manometer 

 to the cell is discussed. 



The cutting of the cells from the cyl- 

 inders is an exceedingly critical opera- 

 tion, which requires experience and well- 

 developed mechanical instincts. Very 

 few, even of those who have had mechanical training, ever succeed 

 in the undertaking. The explanation of so many failures is very 

 simple: The cell wall must not be weakened at any point by the pres- 

 sure of the cutting tools; because, when the cell is baked, the shrinking 

 material (the shrinkage is between 7 and 8 per cent) necessarily draws 

 away from the regions of relative weakness toward those where the 

 cohesion of the particles is stronger and cracks are developed. It is 

 by no means necessary that the damage done by irregular or excessive 

 pressure from the cutting tools should be apparent in the finished 





A 



B 



Fig. 3. 



A. Clay cylinder after pressing. 



B. Clay cell after shaping the cylinder 



(Fig. 3 A) on the lathe. 



