464 



Scientific Proceedings, Royal Dublin Society. 



Iodine Test. 



The series of tests to be described, which are essentially those obtained by 

 Dr. Haanel' using hydriodic acid, are carried out witli iodine alone in the 

 following manner : — 



Iodine is sublimed upon the cover-plate. This is inverted over tlie 

 substance, which is caused to sublime directly upon the existing deposit of 

 iodine. The contact of the hot vapour witli the iodine in a condition of 

 sublimation is sufficient in many oases to produce the iodide which appears 

 when the ascending column of vapour meets the iodine, and is accompanied 

 by a rapid colour-transformation. 



The following table shows the colours of deposits whicli have so far been 

 obtained by sublimation in an atmosphere of sulphuretted hydrogen, and on 

 the iodine-plate described. 



It is found that the colours of deposits produced by these methods are of 

 a greater richness and delicacy than those obtained in the wet way, and 

 slight differences in tint are more surely observed. To obtaia these deposits 

 in sufficient quantities for examination, a few milligrams of the substance 

 are usually sufficient. Experiments have been made which show that tlie 

 place of the iodine may be assumed by other substances, and further tests 

 introduced. 



' Dr. Haanel, Trans. Roy. Soc, Canada, vol. 1, 1883, Sec. 3, p. 65. 



^ Sometimes produced by sublimation on to a deposit of sulphur. 



^ Many of these are more easily obtained in absence of free oxygen. This reaction also is 

 sometimes eifected by subliming the iodine on to the existing sublimate of the substance under 

 examination. 



