214 PROCEEDINGS OF THE AMERICAN ACADEMY. 



these circumstances it seemed worth while to take up the study of the fer- 

 rous iodide, and the results of our work in this field are contained in the 

 following paper. 



Preparation op Ferrous Iodide. 



The method adopted consisted in passing the vapor of iodine over 

 heated iron. In the first experiments a combustion tube was used with 

 a stream of carbonic dioxide to carry the iodine, but as we found a tem- 

 perature above the softening point of hard glass was necessary, we re- 

 placed the glass tube with one of iron, which we heated with a Fletcher's 

 tube furnace. At the high temperature thus obtained the iron was oxi- 

 dized by the carbonic dioxide, and the film of oxide thus formed protected 

 the metal from the action of the iodine ; accordingly the carbonic dioxide 

 was replaced by nitrogen, after which good results were obtained. 



The apparatus in its final form consisted of two large bottles, which 

 served as gas holders for the nitrogen, and were united by glass tubes and 

 rubber connectors in such a way that, by letting in water from the water 

 works, the gas could be forced out of one of them at a regulated rate 

 through the purifiers and the iron tube to the other bottle, in which it 

 was collected. When this was full of gas, by a simple rearrangement 

 of the pinch-cocks the nitrogen could be forced back through the appara- 

 tus again in the same direction as before into the first bottle. By means 

 of this device the same nitrogen could be used over and over again, thus 

 causing a great saving in time and labor. The nitrogen was made by 

 the excellent method of Dr. Gibbs,* — equal parts of sodic nitrite, am- 

 monic nitrate, and potassic dichromate were pulverized, and mixed with 

 three parts of water in a flask with a wide delivery tube. The gas came 

 off when the mixture was gently warmed. Twenty-four grams of the 

 mixture gave about 1200 cc. of nitrogen. The nitrogen, after leaving 

 the gas holder, was purified by passing through a solution of sodic hydrate, 

 sulphuric acid, and a long column of calcic chloride, after which the oxy- 

 gen was removed by means of a layer of finely divided copper heated in 

 a tube of hard glass by means of a kerosene stove. This precaution was 

 necessary, as the nitrogen was contaminated with air introduced when 

 the tubes were opened, or from the water in the gas holders. We tried 

 at first an alkaline solution of pyrogallol for the removal of the oxygen, 

 but as we found this was not efficient, we resorted to the layer of finely 

 divided copper, which was prepared by reducing cupric oxide. 



* Ber. d. chem. Ges., 1877, p. 1387. 



