424 J. G. Diriwiddie — Hydrofluoric and Fluosilicic Acids. 







Table II. 







HaSiFp 



used 



cc. of 



solution 



HF 



used 

 grm. of 

 solution 



KCl 

 added 

 grm. 



NaOH 

 req. 

 cc. 



"NaOH 



theory 



cc. 



Diff. 

 cc. 



10 



4-8818 



3 



19-91 



21-07 



1-16 



10 



5-6151 



1 



21-49 



22-62 



1-13 



10 



102629 



1 



31-12 



32-42 



1-30 



10 



12-2639 



1 



35-37 



36-65 



1-28 



10 



16-3859 



1 



44-01 



45-34 



1-33 



alkali used. This would give a ratio of absorption of one 

 molecule of HF for about 4 of H.,SiF 6 instead of a ratio of 1 :1 

 as Katz* found under these conditions. 



If the precipitate of potassium fluosilicate formed in the 

 presence of free hydrofluoric acid consisted entirely of potas- 

 sium fluosilicate and of free hydrofluoric acid which it absorbed, 

 then by determining the potassium in it, a measure of the 

 fluosilicic acid originally present would be obtained. Or if a 

 known amount of potassium chloride were added for precipita- 

 tion and that remaining in the filtrate determined, the difference 

 would be that Avhich was used up in forming potassium fluo- 

 silicate. For this purpose a standard solution was made of 

 which 10 co contained 0-5090 grams of potassium chloride. 

 Table III gives the results of precipitating potassium fluo- 

 silicate from a solution of fluosilicic acid with and without 

 hydrofluoric acid being present. 











Table III. 













KCl 



H 2 SiFe 



KCl in 



HF 



K Q SiF 6 



KCl 



H 2 SiF 6 



KCl by 



Total 





used 



used 



filtrate 



used 



prec. 



equiv. of 



equiv. 



filtering 



KCl. 





grm. 



grm. 



grm. 



grm. of 

 solution 



grm. 



K 2 SiF 6 

 grm. 





and 

 decomp. 





a. 



0-5090 



0-2634 



0-2381 calc. 





0-4006 



0-27085 



0-2622 











b. 



0-5090 



0-2634 



0-2422 





0-3979 



0-2687 



0-2601 







•5110 



c. 



5090 



02634 



0-2414 





0-3991 



0-2695 



0-2609 







•5109 



d. 



0-5090 



0-2634 



0-2258 calc. 



10 



0-4196 calc. 



2832 calc. 



0-2748 







e. 



0-5090 



0-2634 



0-2288 



10 



0-4169 calc. 



0-2824 



0-2725 



•2785 



•5073 



It will be seen that a, b, and e, each give a precipitate 

 equivalent to a little less than the theoretical value for fluo- 

 silicic acid. This would be expected on account of the 

 appreciable solubility of potassium fluosilicate. 



In d and e, where about 10 grams of hydrofluoric acid were 

 added, in each case the filtrate contained considerably less of 

 potassium chloride than would have been the case if no 

 potassium had been used up except by fluosilicic acid in form- 



*P. 422. 



