VOLTAIC EXCITEMENT AFFECTED BY DILUTION. 
105 
nearly so. Whenever the current existed it was from the weak to the strong acid 
through the liquid. 
1973. When the tube was arranged, as in fig. 9, with water or dilute acid on one 
side only, and the wires were immersed not more than one third of an inch, the effects 
were greatly diminished ; and more especially, if, by a little motion with a platinum 
wire, the acids had been mixed at m, so that the transition from weak to strong was 
gradual instead of sudden. In such cases, even when the wires were moved, hori- 
zontally, in the acid, the effect was so small as to be scarcely sensible, and not likely 
to be confounded with the chemical effects to be described hereafter. Still more 
surely to avoid such interference, an acid moderately diluted was used instead of 
water. The precaution was taken of emptying, washing, and rearranging the tubes 
with fresh acid after each experiment, lest any of the metal dissolved in one experi- 
ment should interfere with the results of the next. 
1974. I occasionally used the tube with dilute acid on one side only, fig. 9, and 
sometimes that with dilute acid on both sides, fig. 10. I will call the first No. 1. and 
the second No. 2. 
1975. In illustration of the general results I will describe a particular case. Em- 
ploying tube No. 1. with strong and dilute nitric acid*, and two copper wires, the 
wire in the dilute acid was powerfully positive to the one in the strong acid at the 
first moment, and continued so. By using tube No. 2. the gavanoineter-needle could 
be held stifly in either direction, simply by simultaneously raising one wire and de- 
pressing the other, so that the first should be in weak and the second in strong acid : 
the former was always the positive piece of metal. 
1976. On repeating the experiments with the substitution of platinum, gold, or even 
palladium for the copper, scarcely a sensible effect was produced (1973.). 
1977- Strong and dilute nitric acid *. — The following single metals being compared 
with themselves in these acids, gave most powerful results of the kind just described 
with copper (1975.); silver, iron, lead, tin, cadmium, zinc. The metal in the weaker 
acid was positive to that in the stronger. Silver is very changeable, and after some 
time the current is often suddenly reversed, the metal in the strong acid becoming 
positive : this again will change back, the metal in the weaker acid returning to its 
positive state. With tin, cadmium, and zinc, violent action in the acid quickly 
supervenes and mixes all up together. Iron and lead show the alternations of state 
in the tube No. 2. as beautifully as copper (1975.). 
1978. Strong and dilute sulphuric acid . — I prepared an acid of 49 by weight, strong 
oil of vitriol, and 9 of water, giving a sulphuric acid with two proportions of water, 
and arranged the tube No. 1. (1974.) with this and the strongest acid. But as this 
degree of dilution produced very little effect with the iron, as compared with what a 
* The dilute acid consisted of three volumes of strong nitric acid and two volumes of water. 
MDCCCXL. 
P 
