486 Moody — Iodometric Determination of Basic Alumina. 



The iodine set free corresponds to the various oxides, to 

 ammonia and to sulphuric acid, therefore, in the following 

 proportions : 



Al.O, 



61 



Fe 2 3 



61 



FeO : 



21 



5ZnO 



81 



NH 3 



I 



H.SO. 



: 21 



The precipitate produced in the hydrolysis contains after 

 ignition the total oxides, A1 2 3 , Fe 2 3 , ZnO. Practically it is 

 more convenient to determine the total oxides in a parallel 

 process, carried on in an open beaker, from which the pre- 

 cipitate may be easily transferred, rather than to attempt to 

 transfer and weigh the precipitate left in the distillation pro- 

 cess. 



Given the total iodine liberated in the distillation process, 

 the weight of the total oxides obtained in the parallel boiling 

 process, the ferrous oxide and ferric oxide by the perman- 

 ganate titrations and the zinc oxide deduced from the corrected 

 electrolytic determination, the total alumina and the basic 

 alumina or free acid (as the case may be) are easily calculated. 



Total oxides — (ferric oxide + ferrous oxide + zinc oxide) = 

 Total alumina. 



( 6> 102^ 97 ) C 7 ' 454 ) X Total alumina = 



iodine equivalent to total alumina. 



( &X lll% 91 ) (*' 76 ^)X ferric oxide = 



iodine liberated by ferric sulphate. 



(2 X 126*9'7\ 

 —— — J (3*532) X ferrous oxide = 



iodine liberated by ferrous sulphate. 



/8xl26-97\ , x 



{ 5X81 . 4 ) (2-496) X zinc oxide = 



iodine liberated by zinc sulphate. 



(t?) 



(7*469) X ammonia = 



iodine liberated by ammonium sulphate. 



Total iodine — (iodine corresponding to total alumina, ferric 

 sulphate, ferrous sulphate, zinc sulphate, ammonium sulphate) 

 = differential iodine. 



(98*08 \ 

 (0-386) 



=free acid. 



