CELLS AND MANOMETER ATTACHMENTS. 5 



ferrocyanide membrane will always be located somewhat nearer the 

 inner than the outer surface of the wall, however large the pores may be. 

 It was evident that the hope of success in cell-making depended on 

 the following conditions: 



1. Great and uniform strength of wall. 



2. The elimination of air-blisters. 



3. An excessively fine and perfectly uniform texture of wall, a texture 

 so fine, in fact, as to insure the meeting of the slower anion and the 

 more mobile cation just within the interior mouths of the pores. In 

 other words, the pores must be so small that the cation is able to pass 

 through them, from the exterior to the interior of the wall, during the 

 time consumed by the anion in just entering them from the interior. 



The necessity of securing great strength of wall is obvious enough, as 

 is also that of eliminating "air blisters," and the need of depositing the 

 membrane at the interior surface of the wall will likewise become appar- 

 ent if one considers the inequalities in the concentration of the solution 

 which must result from its location elsewhere, i. e., within the wall. In 

 the latter case, owing to the slowness of diffusion within the wall, the 

 liquid in the neighborhood of the membrane will be permanently less 

 concentrated than the main body of the solution. Moreover, since the 

 wall is always necessarily filled with some liquid, it would be impossible 

 to know exactly the final concentration of any solution which is intro- 

 duced into the cell. On the other hand, if the discharge of the water 

 entering the cell through the membranes is from a free surface, i. e., 

 directly into the unencumbered solution, the conditions will be favor- 

 able to its rapid distribution, and, therefore, to the maintenance of 

 uniform concentration. 



It was attempted to secure strength of wall by introducing into the 

 clays the maximum allowable portion of cementing material (feldspar) — ■ 

 that proportion, in fact, which is just insufficient to convert the baking 

 cell into porcelain. It was hoped also, by thorough mixing of the con- 

 stituents, to secure a more uniform texture of cell wall than had been 

 found in the products of the potters. 



Washed clays from several sources were mixed with varying quanti- 

 ties of ground feldspar, and the mixtures were burned at different tem- 

 peratures, either in a Seger experimental kiln with use of Seger cones, 

 or in a calibrated electric furnace which was devised for the purpose. 

 The products were altogether disappointing. They were, in reality, 

 quite as uneven in respect to uniformity of strength and texture as the 

 cells of the potters. The failure was evidently due to imperfect mixing, 

 and it was hoped that better results might be obtained with finer mate- 

 rials. Accordingly, both the clays and the feldspar were elutriated, and 

 the wet mixtures of the finer materials thus obtained were passed 

 repeatedly through silk bolting-cloth having 16,000 holes to the square 

 inch. The bolting process was followed by a long-continued churning 



