Tivo 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 prevaihng in England. 



I therefore made choice of the six metals : platina, silve?', 

 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 (acid 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 ammo7iia (of 0'97 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), sz«^^a^e 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 

 w^ater 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 : 

 Fig. 1. C/r^ "^to 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 Avhich 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 

 -^ -S 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 with the plates ; the first, it is true, has 

 long been known to some experimentalists. They are both re- 

 presented of the actual size in the annexed Fig. 2. The first 



