330 Hileman — Alkalimetric Estimation of Silicon Fluoride. 



hydroxide to the point of complete hydrolysis of the fluosili- 

 cate to the condition of a fluoride. 



3SiF 4 + 4H o = 2H SiF. + Si0 4 H 4 

 H 2 SiF fi + 6KOll = 6KF + Si0 4 U 4 + 2H 9 0. 



According to this process the amount of the standard alkali 

 used is three times as great as that used to the end reaction of 

 the preceding process. According to a fourth method advo- 

 cated by Tammann* and useful when fluorides are to be deter- 

 mined in the presence of carbonates, the potassium fluosilicate 

 is precipitated and separated with precautions and titrated by 

 itself with standard potassium hydroxide to the point of forma- 

 tion of potassium fluoride and silicic acid. 



K 9 SiF 3 + 4KOH = 6KF + Si0 4 H 4 



This process is essentially similar to the second process so 

 far as concerns the reaction involved, but only /two units of the 

 alkali used for neutralization are of the standard alkali. For 

 the present purpose therefore, it will suffice to compare the 

 iirst three methods as to the degree of agreement between 

 individual results, and between the averages and the processes. 

 For this purpose measured portions of a solution of fluosilicic 

 acid were treated according to the methods described and the 

 results are recorded in the following table : 







Table I. 









Titration in . 



Alcoholic Solution. 







(According to 





(According to 









Pen field.) 





Bulrnheimer.) 









Standard 



Standard 



Standard 



Fluorine 





[ 2 SiF 6 



NH 4 OH 



KOH 



NaOH 



Found. 



Average, 



cm 3 . 



cm 3 . 



cm 3 . 



cm 3 . 



grm. 



grm. 



25 



7'3 











0-1433 



1 



25 



13 









0-1433 



1 



25 



7-27 







. . _ . 



0-1426 



y 0-1428 



25 



7 23 











0-1429 



1 



25 



7-29 









0-1431 



J 



25 







10-67 







0-J412 



1 



25 







10-72 







0-1419 



1 



25 







10*64 







0-1408 



y 0-14H 



25 







10-67 







0-1412 



1 



25 







10-60 







0-1403 



J 



25 











911 



0-1416 



1 



25 









9-12 



0-1418 



1 



25 











9-07 



0-1410 



y 0-1415 



25 



. 







9*10 



0-1414 



1 



25 











9-12 



0-1418 



J 





* Zeitschr. Anal. 



Chem. xxiv, 328, 



1885. 





