Two Fluids, and of Two Metals not in Contact, 489 
circuit should act so passive a part as is assigned to it accord- 
ing to the theory at present prevailing in England. 
I therefore made choice of the six metals : platina, silver, 
copper, tin, iron, and zinc, [common as well as distilled and amal- 
gamated), In some cases I examined all the combinations which 
might be formed into pairs from these elements ; in most cases^ 
however, I was satisfied with circuits containing zinc, iron, or 
tin, as the positive element, since the three noble metals com- 
bined inter se give rise only to very slight effects. All the me- 
tals were as pure as they could possibly be obtained, and formed 
plates of nearly equal size, viz. somewhat about 3*5 inch in 
length, and 1 inch in breadth. 
The fluids employed were : water, dilute sulphuric acid (acid 
of 1*827 spec. gr. diluted with 9 times its volume of water), 
dilute nitric acid (aeid of 1*321 sp. gr. with 6 times its vol. of 
water), dilute hydrochloric acid (acid of 1*138 sp. gr. with 6 
times its voL of water), saturated solution of chlorine, liquid 
caustic ammonia (of O’ 9 7 spec. gr. diluted with 4 times its vol. 
of water), and solutions of caustic potassa (1 part in weight 
to 4 parts in weight of water), carbonate of soda (1 in 3 water), 
sulphate of magnesia (1 to 3 water), borax (saturated), of 
zinc (1 to 4 water), salt (saturated), sal-ammoniac (saturated), and 
iodide of potassium. (1 part in weight to 4 in weight of water). 
Distilled water was employed for the solutions ; but where the 
water alone was tested, spring water was generally made use of, 
as it conducts better than distilled water, and does not sensibly 
differ in its electromotive action. All the above substances were 
as pure as possible ; thus the sulphuric acid was free from nitric 
acid, the hydrochloric acid from chlorine. 
The mode of performing the experiments was as follows: 
into two small glass vessels (A, B) I 
poured two of the above fluids [a, b) to 
the height of 2*5 inches, placed in each 
a heterogeneous pair of plates (P, N), and 
connected the plates of like nature by 
copper wires, of which one was the wire 
of the multiplier (m), whose needle had to 
indicate by its deflection the presence, the 
direction, and also comparatively the force 
of the electric current. 
Two arrangements, which I will here describe more fully, 
from their great usefulness and manifold applicability in all 
galvanic experiments, served to effect an easy and certain com- 
bination of the wires wdth the plates ; the first, it is true, has 
long been knowm to some experimentalists. They are both re- 
presented of the actual size in the annexed Fig. 2. The first 
