114 



Browning and Flint — Tellurium Dioxide. 



In experiment I, during the evaporation of the acid, there 

 was noticed a slight volatilization of the tetrachloride, which 

 accounts for the increased error. In 2, filtration was per- 

 formed after twelve hours, and the same length of time 

 elapsed in 5 and 6. Experiment 3 stood for two hours, and 

 in this and number 4 potassium hydroxide was used in place 

 of ammonia. So much tellurium was found in the filtrate 

 from 4 that the determination was not completed. In 5 and 

 6, the basic nitrate was dissolved with two cubic centimeters 

 of ten per cent potassium hydroxide solution, instead of the 

 usual hydrochloric acid. Before dilution with hot water, 

 hydrochloric acid was added in very slight excess. The ammo- 

 nia added in number 6 was so much in excess as to dissolve 

 completely the precipitate formed. The increased amount of 

 ammonium acetate produced in the solution probably held up 

 a trace of tellurium. 



In order to observe the effects produced by variations in the 

 factors concerned in the process, several experiments were 

 performed, the figures for which are given in Table III. 







Table III. 









2Te0 2 .HN0 3 



Te0 2 theory : 



Te0 2 







taken 



Te taken as 127-5 



found 



Error 





grm. 



grm. 



grm. 



grm.^ 



(1) 



0-2502 



0-2089 



0-2083 



— 0-0006 



(2) 



0-2524 



0-2108 



0-2110 



+ 0-0002 



(3) 



0-2505 



0-2092 



0-2089 



— 0*0003 



(4) 



0-2528 



0-2111 



0-2106 



— 0-0005 



(5) 



0-253L 



0-2113 



0-2106 



— 0-0007 



(6) 



0-5008 



0-4182 



0-4182 



o-oooo 



in 



0-5010 



0-4183 



0-4175 



— 0-0008 



(8) 



0*5005 



0-4179 



0-4178 



—o-oooi 



The first four and the eighth were allowed to stand over 

 night before the precipitate was removed ; in the fifth one 

 quarter hour, and in the sixth and seventh one half hour, 

 elapsed. By a comparison of the results it appears that very 

 little difference is made whether the time allowed to elapse be 

 from 15 to 30 minutes or 12 or more hours, so long as the 

 liquid is thoroughly cooled. 



In all of the experiments of this series, the basic nitrate was 

 dissolved with ten per cent potassium hydroxide solution, two 

 cubic centimeters being sufficient in the first five, and four in 

 the last three numbers. The solution in the case of the 

 first two was then acidified slightly with hydrochloric acid, 

 before dilution with hot water. In the rest, the alkaline 

 solution was simply diluted with boiling water and faintly 



