322 Mr. H. Giraud on Teiiodide of Chromium, 



method adopted for the production of this compound was 

 similar in character to that which is generally made use of 

 for the formation of the terchloride or terfluoride of chro- 

 mium, 



33*5 grains of chromate of potassa were intimately mixed 

 with 165*45 grains of dried iodide of potassium (the quan- 

 tities being in the proportion of 3 equivalents of iodide of 

 potassium to 1 of chromate of potassa); these materials were 

 then introduced into a tubulated retort, to which a receiver 

 was adapted; about 70 grains of fuming sulphuric acid were 

 then poured upon the materials in the retort ; this instantly 

 gave rise to intense chemical action, accompanied by the 

 evolution of much caloric and the production of heavy gar- 

 net-coloured fumes, which constitute the iodide of chro- 

 mium in a state of vapour : the elevated temperature already 

 induced was sustained by means of a spirit-lamp, and the 

 fumes continuing to come over were condensed in the neck 

 of the retort and in the receiver. A small proportion of free 

 iodine and also of sulphuric acid were carried into the re- 

 ceiver : the products remaining in the retort were sulphate of 

 potassa and green sulphate of the oxide of chromium. 



In every attempt which I have made to procure this sub- 

 stance, with varied proportions of the materials, I have never 

 been able to obtain it quite independent of a small proportion 

 of free iodine and sulphuric acid ; it therefore appears, that 

 it is not essential that the materials should be employed in 

 the exact proportion of their equivalents. The essential 

 changes which occur in the formation of this substance are 

 expressed by the following formula : 



3 KI, (KG + CrO^) and 4 SO^ = 4 (KO + SO^) and Cr F. 



The teriodide of chromium, like the other compounds of 

 that metal, is remarkable for the brilliancy of its colour, 

 which is of a deep garnet hue; it is a fluid of an oily consist- 

 ence, heavier than water, converted into a dense vapour, 

 possessing the same colour as the fluid, at a temperature of 

 about 300° Fahr. ; when exposed to the air it attracts moi- 

 sture, and thence gives rise to watery fumes; by mixture with 

 water it is resolved into chromic and hydriodic acids ; it de- 

 stroys organic substances, gives a black colour to paper and 

 wood, stains the skin of a deep and permanent brownish-red 

 colour, and destroys the cuticle; it is also destructive of 

 animal and vegetable life. 



If the teriodide could be obtained free from adhering sul- 

 phuric acid, its analysis would be easily effected and its com- 

 position determined by means of a soluble salt of lead, a so- 



