JACKSON AND DERBY. — FERROUS IODIDE. 215 



The reaction took place in three steel bicycle tubes, the largest of 

 which was one inch (2.54 cm.) in outside diameter and about one six- 

 teenth of an inch (1.59 mm.) thick. The other tubes were somewhat 

 thinner and small enough to slip tightly into the larger tube. The larger 

 tube contained the iron, which was used in the form of wire clippings 

 (card teeth), as it was found by experiment that these gave a better yield 

 of iodide than turnings, filings, or iron by hydrogen. The iron was freed 

 from organic matter by heating it in a stream of hydrogen before using 

 it. The layer of iron in the tube was about 23 cm. long, and this por- 

 tion of the tube was heated directly by the Fletcher furnace to a bright 

 red heat. One of the smaller tubes was slipped into the larger one at its 

 end nearest the gas holder containing the nitrogen, in this was placed the 

 iodine, which was slowly volatilized by the heat conducted along the iron 

 tube, and the vapor thus formed was swept over the hot iron in the fur- 

 nace by the stream of nitrogen ; this tube was connected with the purifiers 

 by a perforated cork and glass tube far enough from the heat to avoid 

 danger of burning. It was found wise to protect this cork from the 

 iodine vapor, some of which crept back even against the current, by an 

 asbestos or iron diaphragm. The second smaller iron tube was slipped 

 into the further end of the larger tube, and reached the heated portion of 

 it, so that the vapor of ferrous iodide formed in the larger tube condensed 

 in the smaller one, from which it could be easily collected by withdraw- 

 ing this smaller tube after it had cooled in the atmosphere of nitrogen. 

 The joints of the iron tubes were rendered air tight by means of large 

 rubber connectors, which were kept cool by winding them with lamp- 

 wicking that dipped into a beaker of water. The receiving tube just 

 described was connected with some bottles of strong sulphuric acid to 

 prevent the creeping back of any aqueous vapor into the tube. The 

 delivery tube from these bottles conveyed the nitrogen to one of the gas 

 holders already described. 



In carrying on the process it was observed that a considerable amount 

 of iodine was taken up by the iron before any iodide distilled over ; but 

 after it began to appear, it continued to collect for several hours, so that 

 the yield was a good one, and when the apparatus has been once set up 

 the ferrous iodide can be obtained in quantity with little trouble. 



As the product of the reaction just described had a deep red color in 

 thin plates, and looked almost black when the mass was even moderately 

 thick, we supposed at first that it could not be a ferrous salt, and accord- 

 ingly applied the following tests. A little of it treated with water, in 

 which it dissolved completely and with great ease, gave no color with a 



