CRYSTALLIZATION OF A METAL FROM A SOLUTION OF ITS SALT C. C. KIPLINGER, ALLIANCEINSTITUTE OF APPLIEDCHEMISTRY, ALLIANCE.OHIO
The following experiment furnishes a somewhat unusual example of a metal crystallizing from a solution of its salt without the addition of a ., reducing agent or a second metal of a higher electromotive potential. Thirty grams of powdered tin, Baker's 30 mesh, free from copper, arsenic and zinc, with but small traces of lead and iron, was covered with 50 cc. of concentrated HCl (sp. gr., 1.19). After standing a t least 48 hours, to insure maximum conversion of acid to stannous chloride, an equal volume of water was added. This was allowed to stand for a couple of hours and when observed a t the end of this period showed long needle-like crystals groping out of the excess of tin. On pouring off the stannous chloride solution and re-subjecting the excess of granular tin to the action of a fresh supply of concentrated acid for a like period, on dilution the crystals grew rapidly, reaching a length of 1 cm. in five minutes, and increasing to 3 4 4.in about an hour. Only a part of the tin is thus crystallized and the needles seem to spring out of the etched faces of the tin granules. If the concentrated SnCL solution is decanted first and then poured on fresh tin and diluted, the results are unsatisfactory and generally negative. Diluting in the absence of tin and then adding powder also yields no crystals. Groth ("Chemische Krystallographie," Vol. 1, p. 14) states that tetra%anal tin through multiple twinning on the 111 face can form long plates. A study of the tin needles under a low magnification (50 diameters) showed a multitude of striations, the edges of the twinning planes cutting the face of the needle a t an angle estimated to be 45", the angle required for the 111 planes. Groth suggests that tetragonal tin may be formed by the slow electrolysis of a stannous chloride solution, using a weak current, but the case of auto-crystallization herein described is not mentioned and hence this phenomenon would seem to be worthy of note by virtue of its novelty.
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