Miscellanies. 409 
When tin is dissolved in muriatic acid, either by gradual action un- 
der exposure to air, or by the aid of heat, a solution containing an 
excess of acid is obtained. This solution may be concentrated to a sp. 
gr.=1.750, and retains its fluid form at or above 60° F. Although an 
excess of tin is present, the solution thus obtained is always acid. 
After decanting the clear solution, the tin used in excess with its im- 
purities remains, Generally, after a few days exposure, the matters 
left in the solution vessel change in appearance. ‘The dull, corroded 
fragments-of metal become frosted over, with bright needles of tin, 
and beautiful arborescent forms are seen. On studying the cir- 
cumstances, I have found that the effect is due to electrical action. 
One portion of the undissolved tin, becoming a positive electrode, 
while another portion of the same mass assumes the state of a nega- 
tive electrode, and precipitation of the dissolved tin takes place on it. 
Numerous cases of like action are known to chemists, where a part 
of a bar becomes indifferent to a concentrated solution, although a 
Positive state is exhibited at another part, and active sulution of the 
metal is taking place. 
For the purposes of experiment, a solution of muriate of tin, of 
Sp. gr. about 1.650, contained in a cylindrical vessel, may be care- 
fully covered by half its volume of an acid solution of the same, hay- 
ing a sp. gr. about 1.20. The two fluids should not be mixed more 
than the slight diffusion which will take place. After placing a flat 
bar or plate in an inclined position, so that it passes through both so- 
lutions, the effects become immediately perceptible. That part of the 
bar which is within the diluted solution takes the positive state. A 
few minute bubbles of hydrogen form and escape, if the solution is 
quite acid. Precipitation of metallic tin commences near the line of 
contact of the two solutions, and extends throughout that part of the 
bar immersed in the denser solution. If the diluted solution is not 
rendered acid by the addition of acid, hydrogen is not perceived, and 
the action is more gradual. In either case the precipitation contin- 
ues until the two fluids have attained the same electrical relation to 
the bar. If after the precipitation has ceased, water be carefully 
poured upon the surface of the fluid, it will form a stratum of very 
dilute solution. That part of the bar not before immersed takes the 
hegative relation to this solution, and the same kind of precipitation 
follows as had taken plaee in the lower solution. The positive part 
of the bar, retains its state unaltered under the new conditions, and 
the line of separation is as clearly defined as in the first case. Ifa 
solution mixed with crystals be used, instead of a moderately concen- 
trated solution, they are not decomposed under the above conditions. 
The presence of atmospheric oxygen has my supposed to influence 
Vol. xxxvimt, No. 2.—Jan.-March, 1840. 
