Ilileman — Alkalimetric Estimation of Silicon Fluoride. 335 



The cause of the variation in the results, and of the occa- 

 sionally very large errors in the above series of experiments, 

 was not apparent at the time when the experiments were made, 

 but reference will be made to this later. 



Crystals of nuorite, perfectly clear and of a pale green color, 

 were next tried. The powdered mineral on treatment with 

 sulphuric acid yielded the theoretical amount of calcium 

 sulphate. 



Table VI. 









Fluorine 



Fluorine 



Flourine 





Tem- 





CaF 2 



KOH 



Theory 



Found 



Error 



Time 



pera- 





grams. 



cm 3 



grams. 



grams. 



grams. 



hours. 



ture. 









(I"* = 0-01045 Fluorine.) 







1. 



0-5000 



21-77 



0-2432 



0-2274 



— 0-0158 



6 



[150° 



2. 



0-5000 



22' 



0-2432 



0-2299 



-0-0133 



6 



j 160° 



3. 



0-5000 



31-77 



0-2432 



0*2274 



— 0-0158 



3-25 



I 



4. 



0-5000 



23-6 



0-2432 



0-2466 



— 0-0034 



6 



1 



5. 



0-5000 



22-15 



0-2432 



0-2314 



— 00118 



6 



[►180° 



6. 



0-5000 



22-19 



0-2432 



0-2318 



-0-0114 



6 



7. 



0-5000 



19-37 



0-2432 



02014 



— 0-0418 



6 



1 



8. 



0-5000 



16-2 



0-2432 



0-1692 



— 0-0740 



3 



J 



9. 



0-5000 



22-2 



0-2432 



0-2325 



— 0-0107 





| boil- 



10. 



0-5000 



21-25 



0-2432 



02220 



— 0-0212 





s' m S- 



In experiment (1) above, the heating was continued for six 

 hours at 150-160°. In experiment (2) the powdered mineral 

 was fused with sodium carbonate and the mixture transferred 

 to the decomposition flask. In experiments 2-8 above, the 

 temperature was raised as high as 180°, while the empty 

 U-tube was immersed in a freezing mixture of salt and ice. 

 Blank determinations showed that some sulphuric acid was 

 carried over under these conditions. In experiments (9) and 

 (10) the -acid was heated to boiling and allowed to cool before 

 the air current was passed through. 



The effect of precipitated silica instead of quartz sand was 

 next tried. In experiment: (1) the silica was air dried ; in (2) 

 it was strongly ignited. 









Tabi 



,E VII. 



Theory 



Found 



Error 



CaF 2 



Silica 



KOH 





Fluorine 



Fluorine 



Fluorine 



grams. 



grams. 



cm 3 





grams. 



grams. 



grams. 



1. 0-5000 



7-0 



6-4 





0-2432 



0-0668 



0-1764 



2. 0-5000 



7-0 



21-2 





0-2432 



0-2215 



0-0217 



These experiments indicate that the small amount of water 

 in the air dried silica may cause great deficiency in the fluorine 

 found, and suggests the idea that even the amount of water 

 produced in the reaction involving the sulphuric acid, the 

 fluoride and silicon dioxide may be the occasion of trouble. 



