M. Carey Lea — Properties of Allotropic Silver. 241 



Art. XXX Y. — On Ring Systems arid other Curve Systems 

 produced on Allotropic Silver by Iodine • by M. Carey Lea. 



Allotropic silver, in its moist and plastic state, may be 

 brushed over paper and gives on drying a continuous and brill- 

 iant coating resembling metallic leaf.* When a small crystal 

 of iodine is placed on paper that has been thus coated, a system 

 of colored rings of remarkable beauty is obtained. A funnel or 

 beaker should be inverted over the paper to prevent distortion 

 by irregular currents of air. One form of distortion, however, 

 produced by a slight current in one direction, gives interesting 

 results. If the paper with the crystal on it is set near a closed 

 window, the slight current which makes its way through, 

 affects the air under the glass enough to carry the iodine vapor 

 principally in one direction and there result oval or pear- 

 shaped curves of great elegance and much variety according as 

 the air currents are stronger or weaker. Another method is to 

 place a bell glass, not fitting too closely, over the paper and 

 to set it where it will be influenced by the draught created by 

 a fire, or even by a gaslight. 



That iodine is capable of producing interference rings 

 (JSTobili's rings) on metallic surfaces has long been known, and 

 Robert Hunt has described their formation on surfaces of 

 normal silver. I have made these for comparison, pressing 

 gummed paper on silver leaf, bringing to a smooth surface by 

 gently rubbing after drying. The contrast between the pale 

 and faded-looking effects produced on normal silver, and the 

 lustrous and glowing hues given by the allotropic, is very 

 striking. f One cannot help wishing that this splendid colora- 

 tion could be made to do service for obtaining natural colors 

 by photographic processes. 



As to the durability of these products, I cannot yet speak 

 with positiveness. Protected from light and air they endure 

 for several months at least. Both the bluish green insoluble 

 silver B, and the gold-colored C produce these effects ; the gold- 

 colored is the better suited of the two. 



July, 1889. 



♦Described in this Journal, June, 1889. 



1 1 was desirous of having some of these curve systems reproduced in color 

 printing for this Journal, but on conferring with an experienced color printer, 

 found that he could give no assurance of a successful result. The colors are trans- 

 parent, and yet have a metallic brilliancy, a combination almost impossible to 

 imitate in printing. 



