Method for the Estimation of Telluric Acid. 377 



added. The oxidation was accomplished from this point ex- 

 actly as in series I, the only difference being that it took place 

 in the presence of a slight excess sulphuric acid instead of in 

 alkaline solution. The permanganate used in both series was 

 standardized ultimately against lead oxalate. 





Series 



I. 





Te0 2 taken. 



Oxygen required 



Molecular weight 



grm. 



for oxidation. 



of Te0 2 when = 16 



0-1200 



0-01202 





159-7^ 



0-0783 



0-00785 





1596 | 



0-0931 



0-00940 





158-7 ! 

 158- [ 



o-iioo 



0-01119 





0-0904 



0-00909 





159-5 | 



0-1065 



0-01078 





157-8 J 





Series 



IT. 





0-0910 



000935 





159-2 "J 



0-0910 



0-00910 





159-9 | 



0-0911 



0-00924 





157-7 1 

 159-6 f 



0-0913 



0-00915 





0-0912 



0-00915 





159-4 | 



0-0914 



0-00923 





158-4 J 



Mean. 



158-88 



159.03 



The mean value of these determinations assigns to the tellur- 

 ous oxide which we employed a molecular weight of about 159 

 and to the element tellurium an atomic weight of 127, when 

 oxygen is 16. Brauner advocates the application of a correc- 

 tion made necessary by the excessive decomposition of the 

 permanganate in the oxidation ; but inasmuch as the oxidation 

 in series I took place in alkaline solution under conditions in 

 which we have no absolute proof that unused oxygen is liber- 

 ated to any considerable degree from the permanganate, while 

 in series II, the excess of sulphuric acid was purposely 

 restricted to the lowest limit — the sulphuric acid having been 

 shown in a previous paper from this laboratory* to be the 

 chief agent in inducing the excessive decomposition of the 

 permanganate — we incline, provisionally at least, to accept in 

 this case the result of the analysis without correction. 



In the test experiments the telluric acid, prepared in the 

 manner described, was introduced into the apparatus for dis- 

 tillation with 3 grms. of potassium bromide, care being taken 

 to insure in the 50 cm 3 or more of liquid the presence of 

 10 cm 3 of sulphuric acid of half strength. A current of car- 

 bon dioxide was passed through the apparatus, the solution 

 was boiled to set free the bromine which was absorbed in 



* Gooch and Danner, this Journal, xliv, 301. 



