416 



PROCEEDINGS OP THE AMERICAN ACADEMY. 



Nine such duplicate experiments were made. The first of these was 

 a crude trial, and need not be recorded ; the eight others are given iu 

 the following table. 



The apparatus employed was precisely like that described in the pre- 

 vious paper. For the sake of easy reference, the description is repeated 

 below. 



Small cylinders of Pukal's porous ware (Berlin), suitable for osmotic 

 pressure experiments, were used to enclose the anode in order to prevent 

 the heavy anode-solution from reaching the kathode. These vessels 



were 50 millimeters high and 



— J A ^ 20 in diameter ; their walls 



were not much over one milli- 

 meter in thickness. Their 

 impurities were removed by 

 boiling with nitric acid and 

 thorough washing with water. 

 Before being used they should 

 be carefully searched and 

 tested for cracks or imperfec- 

 tions. They were suspended 

 in the solution by means of a 

 platinum wire hung upon *a 

 glass hook, which insulated 

 the wire from the electric 

 connections. By means of a 

 siphon, or a small pipette 

 with a rubber top, the liquid 

 within the cup was always 

 kept at a lower level than 

 that without, so as to prevent 

 outward filtration. 



The kathodes consisted of 

 large crucibles weighing only 

 GO grams, although they were 

 capable of holding 120 cubic 

 centimeters ; they were pro- 

 vided with lips. A crucible 

 exposes a smaller surface of 

 liquid to the impurities of the atmosphere, and gave in our expeiuments 

 a more evenly distributed deposit than a bowl. 



-«^ 



FiGDRE 1. — rOKOUS CuP VOLTAMETER 



(I actual size). 



A, glass hook for supporting anode. B, glass 

 ring for supporting porous cup. C, silver anode. 

 D, porous cup. E, platinum kathode. 



