676 TRANS. ST. I.OUIS ACAD. SCIENCE. 



Iodine in Blowpiping. 



By H. A. Wheeler and C. Luedeking. 



The first application of iodine in blowpiping was made by Bun- 

 sen (Ann. Chem. & Pharm., vol. cxxxviii.) in 1866, who used the 

 iodine as a secondary reagent. He first obtained, as is well known, 

 the oxide films on a porcelain dish and then converts these into 

 the iodide films by means of hydriodic acid. As a direct reagent 

 we find iodine first used by von Kobell (Journ. Prakt. Chem., vol. 

 cxii.) in 1 87 1, for the detection of bismuth and lead, in the form 

 of bismuth flux.* In 1883 Dr. E. Haanel (vol. i. Proc. Roy. Soc. 

 Canada) made a great step forward by using hydriodic aeid 

 directly. 



As performed by Dr. Haanel, he moistens his substance with 

 hydriodic acid on a suitable support and then gently heats, when 

 he obtains the volatile iodides of the more fusible metals. By this 

 direct application he is able to secure several new reactions in 

 addition to those of Bunsen. 



As these iodides generally have very characteristic and striking 

 colors, it becomes a valuable method for distinguishing as well as 

 detecting very small quantities of these substances. 



The hydriodic acid is prepared by passing sulphuretted hydro- 

 gen gas through water having in suspension iodine in excess, ac- 

 cording to the well known method. If this reagent is used on the 

 charcoal support, only partially satisfactory results are obtained, 

 on account of its almost absolute nonconductivity of heat, while 

 its color not only makes a poor background to show off the coats, 

 but also compromises and modifies the true tint. 



If, however, we take thin tablets of plaster of paris, we have a 

 substance that rapidly chills and condenses the volatile iodides, 

 while the pure white background not only shows the slightest 

 amount of coloring matter, but also shows it in its true color. 

 These tablets are made by pouring a thin mixture of plaster of 

 paris and water upon a smooth flat surface, preferably a glass plate, 



* Bismuth flux consists of a mixture of equal parts of flowers of sulphur and iodide of 

 potassium. 



