Miscellanies. 409 



When tin is dissolved in muriatic acid, either by gradual action un- 

 der exposure to air, or by the uid 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 stale 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, hav- 

 ing a sp. gr. about 1.20. The two fluids should not be mixed more 

 than the slight diftusion which will take place. After placing a fldfc 

 bar or plate in an inclined position, so that it passes through both so- 

 lutions, the etfects 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 solutioii. That part of the bar not before immersed takes the 

 negative relation to this solution, and the same kind of precipitation 

 follows as had taken place 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. If a 

 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 been supposed to influence 

 Vol. sxxviii, No. 2.— Jan.-March, 1840. 52 



