Moody — lodometrio Determination of Aluminium. 183 



In Table III are shown results of the application of the 

 process to an ammonium alum. 



Table III. 



Approx. — 



Ammonium 

 alum. 

 cm 3 . 



25 



25 



25 



25 



25* 



25* 



25 



25 



25 



25 



KIO s . 



KI. 



Time in 



grm. 



grm. 



minutes. 



0-3 



1-0 



20 



0-3 



1-0 



15 



0-3 



1*0 



20 



0-3 



1*0 



25 



0-3 



10 



12 



0*3 



1-0 



12 



0-3 



l'O 



20 



0-3 



1-0 



25 



0-3 



2-0 



25 



0-3 



2-0 



20 



Approx. — 



Na 3 S a 8 . 

 cm 3 . 



25-20 



25-17 



25-10f 



25-20f 



25-70J 



24-65f 



25-20J 



25-15J 



25-20f 



25-15J 



A1 2 3 



calculated 



grm. 



0-0429 

 0-0429 

 0*0427 

 0-0429 

 0-0421 

 0-0420 

 0-0430 

 0*0429 

 0-0430 

 00429 



Diff. 

 grm. 



+ 0-0007 

 + 0*0007 

 + 0-0005 

 + 0-0007 

 — O'OOOl 

 -0-0002 

 + 0-0008 

 + 0-0007 

 + 0-0008 

 + 0-0007 



These results proved to be too high and led to the conclu- 

 sion that the ammonium sulphate was acted upon by the iodic 

 mixture, liberating an additional portion of iodine. Experi- 

 ments with ammonium sulphate verified the supposition, and 

 the process is, therefore, less accurate in the presence of 

 ammonium salts. In fact, ammonium sulphate in the amounts 

 taken may be completely hydrolyzed in the course of three 

 hours, about one-half of the iodine liberated by the sulphuric 

 acid formed in the hydrolysis being available for estimation 

 under the conditions of the foregoing determinations. When, 

 however, the distillate is collected in a solution of potassium 

 iodide containing sufficient acid to combine with the ammonia 

 volatilized, iodine is liberated in amount equivalent to the 

 entire quantity of sulphates present, and may be titrated with 

 sodium thiosulphate. 



The reaction between iodine and ammonia in alkaline solu- 

 tion, and the hydrolysis of ammonium salts, are undergoing 

 further investigation by the writer. 



The attempts to obtain a complete reaction by heating the 

 mixture in a pressure bottle showed that the results of this pro- 

 cedure are low, although but slightly deficient, and cannot be 

 used for estimating correctly the amount of aluminium salt in 

 the solution. 



The following method can be recommended as one giving 

 constant results which correspond closely with the gravimetric 



* Liquid in Voit flask not clear, 

 f New standard. 



\ New standard. 



