J. G. Dinwiddle — Hydrofluoric and Fluosilicic Acids. 429 







Table IV. 









NaF 



NaCl 



KSCu 



N.HC1 



FeCl 3 sol. 



No. 



cc. 



grm. 



cc. 5% 



cc. 



cc. 



1. 



10 



10 



5 



o-o 



11-50 



2. 



10 



10 



5 



o-o 



11-55 



3. 



10 



10 



5 



o-o 



11-53 



4. 



10 



10 



5 



o-i 



11-11 



5. 



10 



10 



5 



0-2 



10-63 



6. 



10 



10 



5 



0-4 



10-10 



7. 



10 



10 



5 



0-6 



9-66 



8. 



10 



10 



5 



0-8 



8-88 



9. 



10 



10 



5 



1-0 



8-39 



10. 



10 



10 



5 



2-0 



5-90 



11. 



10 



10 



5 



4-0 



3-45 (' 



12. 



10 



10 



5 



l co (then 



11-65 











neutralize) 



13. 



10 



10 



5 



5 cc a 



11-50 



14. 



20 



20 



10 



o-o 



23-12 



15. 



20 



20 



10 



o-o 



23-14 



with. The results show that with proper care a solution of 

 alkali fluoride can be obtained nearly enough neutral to give 

 quite an accurate determination. 



Greef claims that by the use of the ferric chloride method 

 he can estimate the amount of sodium hydrogen fluoride which 

 is present in a mixture containing sodium fluosilicate. Greef's 

 directions for this determination are as follows : " Titrate a 

 weighed portion of the mixture in hot water solution with 

 standard sodium hydroxide using phenolphthalein as indicator. 

 In this now neutral solution, determine the total fluorine by 

 titration with standard ferric chloride solution as described 

 above. Dissolve another portion of the mixture in a small 

 volume of water and, after addition of alcohol until the con- 

 centration is approximately 50 per cent in alcohol, add about 

 one gram of potassium chloride and titrate with the standard 

 sodium hydroxide until neutral to phenolphthalein." In cal- 

 culating the results from data obtained by following the above 

 directions, Greef assumes that the alkali used in the alcoholic 

 titration is a measure of the total free hydrofluoric acid in the 

 mixture and that in the water titration for each equivalent of 

 sodium hydrogen fluoride, one equivalent of alkali is required, 

 while for each equivalent of sodium fluosilicate four equivalents 

 of the alkali are used. From the total fluorine as found by the 

 ferric chloride titration and from the results obtained in the 

 water and in the alcohol titration, Greef calculates the content 

 of the original material in sodium fluosilicate, sodium fluoride 

 and sodium hydrogen fluoride according to the following 

 equations : 



