154 
PROFESSOR DANIELL ON VOLTAIC COMBINATIONS. 
which the value of A (in the formula ^ * •— a) most nearly approaches to CL5. 
It will therefore vary even in batteries of the same chemical construction ; increasing 
as R diminishes in proportion to r : or in other words, when the plates are large, a 
more numerous series is required, than when small, to produce the most advantageous 
results. This is likewise the case when the exterior resistance is increased : in both 
cases R is virtually diminished in respect to r. 
It is evident from the preceding observations, that all the comparisons hitherto made 
by different experimenters between the general relative powers of different batteries 
are faulty, inasmuch as they only hold good in the particular cases to which the ex- 
periments are limited ; and one battery of a certain size may be preferable for one 
kind of decomposition, and yet may allow of considerable useless expenditure of 
power when a different electrolyte is subjected to its action. As, however, great 
stress has, by some, been laid on comparisons of this kind, it may not be amiss to 
give a few experimental results. 
In the following arrangements the cylindrical form was employed. In each case 
the platinum cylinders were 4 inches high, and If inch in diameter. The zinc 
rods were half an inch thick, the exciting fluid was placed in a porous earthenware 
tube 1 inch in diameter. Three cells was the number employed in each experi- 
ment. The measures employed was the quantity of mixed gas produced from the 
voltameter during 5 minutes. 
Exterior liquids. 
Exciting liquids. 
Gas in five minutes. 
Acid sulphate of copper 
Dilute sulphuric acid, specific gravity 1*126 
Dilute sulphuric acid, specific gravity 1*126 
Dilute sulphuric acid, specific gravity 1*126 
Dilute sulphuric acid, specific gravity 1*126 
Dilute sulphuric acid, specific gravity 1 4 126 
Dilute nitric acid, specific gravity . . I 4 05 6 
cubic inches. 
30 
14-0 
31 
5 5 
3-5 
8'5 [ 
Nitric acid, specific gravity 1'40 
Bichromate of potash, specific gravity l 4 050. . 
Bichromate of potash, 4 sulphuric acid 
Nitrate of copper, neutral saturated solution 
Nitric acid, specific gravity V40 
The eligibility of a liquid in the construction of a battery will, of course, be much 
influenced by its conducting power : and it would at first sight appear that this 
might be easily determined by placing the different liquids, in succession, in the same 
voltameter, or experimental cell, and transmitting through them a constant current 
of known power ; measuring the retarding influence of each by another voltameter 
charged in the usual way with dilute sulphuric acid, and included in the same circuit. 
The following are the results of some experiments so performed. The current from 
ten cells of the small constant battery was employed : — 
Liquid tested. Gas from voltameter in five minutes. 
Cubic inches. 
Nitric acid, specific gravity 1*4 .11 
Nitric acid -f- sulphuric acid . 11 
Dilute sulphuric acid (standard) 9'2 
Dilute sulphuric acid saturated with sulphate of copper . . 9‘2 
Saturated solution of sulphate of copper 7‘9 
Bichromate of potassa, specific gravity T050 5'6 
