A NOTE ON PLASTIC AND ALLOTROPIC FORMS OF SULFUR RICARDO CARVALHO PERREIRA Sao Paulo, Brazil
SCAAEFER
will show striking plastic properties. It is a rubber-like substance with a beautiful lemon-yellow color and after distention to three times its length it regains its original form. In less than one hour from the moment it is ohtained it becomes hard and brittle. This "condensed" sulfur seems to be a plastic sulfur different from the common gamma-sulfur. This view is supported by the difference of colors, the gamma-sulfur being dark. The author could not study the crystalline stmcture of the thin layers because he has no suitable apparatus. But, observed through a Bausch & Lamb wide-field stereoscopic microscope, this plastic mass seems to he composed of very small SCHAEPER,H. F.,AND G.D. PALMER,J. CHEM.EDUC., 17, rhombic or monoclinic crystals surrounded by com473475 (1940). paratively large airpockets. The air finally escapes and *See, for instance, J. R. PARTINGTON, "A College Course of Inorganic Chemistry," Maomillen and Co., Ltd., London, 1939, the sulfur loses all its plastic properties. AND PALMER' gave a very complete summary of the several allotropic forms of sulfur as well as of plastic sulfur. But even in such an exhaustive r 4 sum6 the author could not find any reference to an interesting modification of plastic sulfur he observed and which certainly has been observed by many others. When we heat sulfur in a test tube it boils and a red vapor is evolved which becomes yellow when strongly heated.2 Now, if we pour this yellow vapor into a porcelain dish filled with cold water, it will be condensed a t the water surface as a very thin sulfur layer-of less than 0.2 mm. If this sulfur layer is picked up, it
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