-±8i Moody — lodometric Determination of Basic Alumina. 



The commercial aluminium sulphates, including the alums, 

 may contain sulphates other than aluminium sulphate, which 

 are susceptible to hydrolytic action. Ferrous sulphate, ferric 

 sulphate and zinc sulphate are common impurities ; and 

 ammonium sulphate is a constituent of ammonium alum. 

 The effect of each of these sulphates in liberating iodine has, 

 however, been studied. Potassium sulphate and sodium sul- 

 phate, if present, do not set free iodine from the boiling solu- 

 tion containing the iodide-iodate mixture. The determination 

 of the ferrous iron, the ferric iron, the zinc, and the ammonia 

 will furnish data from which the equivalent amounts of sul- 

 phuric acid, to be taken into account in the reckoning of the 

 free acid or basic alumina, may be calculated. The behavior 

 of these commercial products toward the iodide-iodate mixture 

 should, therefore, afford an easy method of determining basic 

 alumina or free acid, as the case may be. 



Following are details of 

 treatment, and the results ob- 

 tained in applying this method 

 of analysis to certain samples 

 of commercial alum, kindly 

 submitted for the purpose by 

 Dr. F. S. Havens, whose 

 courtesy I desire to acknowl- 

 edge. 



Of the finely powdered 

 material a portion of 15 grms. 

 was weighed and treated with 

 water. The solution was fil- 

 tered and made up to 1 liter. 

 The material which did not dissolve was dried at 100° and 

 weighed as insoluble 7naterial • of the solution a portion of 

 25 cm3 was titrated directly with standard potassium perman- 

 ganate to find the amount of iron in the ferrous salt, and 

 from this was calculated the ferrous oxide. 



Another portion of 25 cm3 was reduced with zinc in the 

 usual manner and titrated with the permanganate to give the 

 total iron. From the difference between the total iron and 

 the ferrous iron was reckoned the ferric oxide. 



To determine the zinc a portion of 25 cm3 was diluted to 

 50 cm3 , treated with 3 grms. of sodium acetate and l cm3 of acetic 

 acid, and electrolyzed with the use of the rotating cathode* 

 and a current of about 2 amperes for 30 minutes. The 

 deposit of zinc, including some iron, was washed with alco- 

 hol, dried and weighed. The solution of the deposit in 

 sulphuric acid was titrated with permanganate, the amount of 

 * This Journal, xv, 320. 



