Dr. Schuuck on the Formation of Indigo-blue. 117 



to errors of observation. The equivalents differ also by one, and 

 are not equally great, as has hitherto been generally assumed. 



Weber describes* the preparation of iodide of aluminium. 

 One part of aluminium in filings is placed in a sealed tube, and 

 ten or eleven parts of dry iodine added. The tube is then sealed 

 at the other end and gently heated. Combination takes place 

 with sti'oug evolution of light and heat ; the granules of alumi- 

 nium burn with a splendid violet light. On cooling, the iodide 

 appears as a solid mass coloured brown by excess of iodine ; by 

 using a slight excess of metal, and resubliming the iodide once 

 or twice, it is obtained pure. It forms then brilliant white cry- 

 stalline laminse, which melt to a very mobile liquid ; on further 

 application of heat this boils readily, and sublimes in delicate 

 snow-white laminse in the colder part of the tube. Exposed to 

 the air, it fumes strongly, and readily deliquesces. Heated in 

 the air it decomposes with the liberation of iodine. The formula 

 of the iodide is AV^ P, quite analogous to the chloride. Iodide 

 of aluminium forms with water a compound which is probably a 

 hydrate. It also forms with iodide of potassium a double com- 

 pound. This is a waxy, transparent, crystalline mass, which readily 

 melts, but sublimes with difficulty. It has the formula Al'' P Kl. 



XVI. On the Formation of Indigo-blue. — Part II. 

 By Edward Schunck, Ph.D., F.R.S. 

 [Continued from p. 45.] 

 Indifidvine. 



THIS substance is obtained, on the evaporation of its alcoholic 

 solution, in the form of a deep reddish-yellow, transparent, 

 amorphous resin, which when dry is brittle, and may easily be 

 reduced to powder. It is perfectly insoluble in caustic alkalies, 

 a property by which it may be at once distinguished from indi- 

 retine, which it i-esemblcs in its outward appearance. Even 

 when grape-sugar or protochloride of tin is added to the alkaline 

 liquids, not a trace of it dissolves even on boiling, and in this 

 respect it differs widely from indirubine. When it is treated 

 with strong caustic soda-lye, only a trace of ammonia is given 

 off, but on heating the dry substance with soda-lime, there is a 

 very perceptible evolution of ammonia. When heated on pla- 

 tinum it melts and then burns with a briglit flame, leaving much 

 charcoal which burns away with difficulty. On being lieated in 

 a tube, it melts and gives off fumes having a strong smell, resem- 

 bling that of crude indigo when heated. These fumes condense 

 on the colder parts of the tube to a brown oil, which on cooling 

 ♦ Poggcndorff' 8 Annalen, July 1857. 



