Electrolysis of Secondary Compounds. 179 



hollow ring of glass, also ground on either side, with a flat 



shoulder to fit against the two half cylinders, which are pressed 

 home by the screws. Each side of the ring is furnished with 

 a rim, which is grooved to admit of a thin piece of bladder 

 being tied over it to form a kind of drum ; at K is a small 

 hole to admit of the cavity being filled with a liquid. D and 

 E are two bent tubes, fitted to the two half cylinders for col- 

 lecting the gases evolved in the experiments, g and h are two 

 circular platinum electrodes connected by wires, 2,y (passing 

 through corks in the necks of the half cylinders), with the bat- 

 tery. The apparatus when adjusted forms three compartments, 

 each of which may be filled with the same or a different liquid, 

 and the whole may be supported on a light frame of wood. 



We will not attempt to describe the particulars of every 

 experiment referred to in the following pages, for their number 

 is very great, and their details would be both tedious and 

 useless ; we will only select some of the principal, in the results 

 of which we can trace no ambiguity; and have no doubt we 

 shall obtain credit for every care in determining the purity of 

 the substances which we employed, and in making the various 

 analyses which were required. 



(a.) A strong solution of tribasic phosphate of soda and 

 water (2NaO, HO, Pg O5) (rhombic phosphate) was placed in 

 the platinode cell of the diaphragm apparatus; the centre cell 

 and the zincode cell were both charged with a dilute solution 

 of soda (:pV)" ^^^ power of twenty cells of the small constant 

 battery was transmitted through it, oxygen was evolved at the 

 zincode, and in thirty-seven minutes 48 cubic inches of hy- 

 drogen were collected from the platinode ; the experiment was 

 then stopped and the solutions examined. 



N2 



