350 Professor Daniell on the 



to the amount of electrolytic force in action, with a view to 

 increase our knowledge of the constitution of saline bodies in 

 general. 



For this purpose an apparatus was constructed in the fol- 

 lowing manner, which Mr. Daniell calls " the double dia- 

 phragm cell." 



" It consists of two cells formed of two glass cylinders, with 

 collars at their lower ends, fitted by grinding to a stout glass 

 tube bent into the form of the letter U, and firmly fixed on 

 a wooden foot. The ends of this piece project, a little into 

 the interior of the two cylinders, the upper extremities of 

 which are furnished with bent tubes for the collection of 

 gases. A stout piece of platinum wire is ground to the upper 

 part of each cell, to which an electrode of platinum or any 

 other metal can be screwed on the inside, as occasion may 

 require : the wires pass down upon the outside, and terminate 

 in two mercury cups, by which connexion can be made, at 

 pleasure, with the battery. Each cell will hold about seven 

 cubic inches of liquid, and the connecting tube two inches. 

 When the cell is charged, the connecting tube is filled with 

 the liquid, and a piece of fine bladder tied over each end, so 

 as perfectly to exclude the air. The bladders are firmly con- 

 fined to their places by means of circular grooves ground 

 round the ends of the glass tube. The cylinders are then 

 carefully fitted to their places, and filled with the proper 

 quantities of the solutions to be acted upon, and after the 

 operation their contents are easily decanted." The quantity 

 of liquid in each cell during the experiment was about 4*5 

 cubic inches. The power employed was that of a small con- 

 stant battery of Mr. DanielPs construction, containing thirty 

 cells six inches in height, with tubes of porous earthenware, 

 charged in the ordinary manner. (See Phil. Trans, for the 

 year 1836.) 



From this battery the current was made to pass through 

 the apparatus just described, filled with a solution of the salt 

 to be examined, say sulphate of soda. A common voltame- 

 ter charged with dilute sulphuric acid, was also included in 

 the circuit, so that the mixed gases evolved might be collected, 

 in order to ascertain the exact amount of electrolytic force 

 really in circulation. 



The gas given off from each side from the double dia- 

 phragm cell was also collected, and the united bulk of the 

 oxygen and hydrogen so evolved was found to be exactly 

 equal to the volume of the mixed gases collected from the 

 common voltameter. From numerous experiments it was found, 

 that on decanting the saline liquid from each cell, and care- 



