4 OSMOTIC PRESSURE OF AQUEOUS SOLUTIONS. 



good and bad behavior of the porous wall of the cell are susceptible of 

 clear definition and of adequate explanation. All the essential facts 

 which had been discovered in the laboratory were given to the potters, 

 and they expressed their confidence in their ability to remedy the 

 defects of the earlier consignment. In this expectation they were 

 greatly mistaken; for, among the nearly 500 cells which were subse- 

 quently made for us at various potteries, not one was found suitable for 

 the measurement of osmotic pressure. In fact, in attempting to remedy 

 certain defects, they generally aggravated others to such an extent as to 

 render the later cells on the whole distinctly inferior to those of the first 

 lot. Finally we ventured to offer certain suggestions involving methods 

 of manufacture not in use among potters, but these were rejected on 

 the ground that, to those familiar with the conduct of clays, they were 

 obviously futile. As the potters declined to cooperate along lines of 

 manufacture not approved by them, the problem of cell-making was 

 taken out of their hands into the laboratory for solution. 



The cells produced at the potteries were defective in various ways, 

 but principally in the particulars enumerated below: 



1. All were lacking in the strength necessary to withstand any con- 

 siderable outward pressure. As mentioned above, only one of the few 

 which proved at all serviceable survived a pressure of 30 atmospheres, 

 while most of them cracked under pressures below 20 atmospheres. 



2. All of them contained numerous "air blisters," which communi- 

 cated with each other and with the interior surfaces of the porous wall 

 in such ways as to give rise to the formation of a number of subsidiary 

 interior membranes. Not unfrequently, when a cell was broken for 

 examination, as many as four or five of these minor membranes, often 

 nearly concentric over a considerable area, were found in several local- 

 ities; and it frequently happened also that the last of them was near, or 

 even at, the exterior surface of the cell. 



3. The potters' cells also lacked uniformity in respect to porosity. 

 The same cell would often exhibit the greatest diversity in this par- 

 ticular. In some parts, the structure would be as close as in porcelain, 

 while in others it might be so open that the membrane would form 

 nearly midway between the interior and exterior surfaces of the cell 

 wall. 



A miscroscopic examination of thin sections of the cells in which 

 membranes had been deposited revealed the fact that, excluding the 

 peculiar and often fantastic effects of "air blisters," the distance of the 

 membrane from the interior surface of the cell wall is determined solely 

 by the porosity of the latter. The more open the texture is, i. e., the 

 larger the pores are, the more deeply within the wall will the deposition 

 occur; while with a certain degree of closeness in this respect, the depo- 

 sition is just within the interior entrances of the pores, in effect, upon the 

 inner surface of the cell, where it should be. Obviously the copper 



