334 Hileman — Alkalimetric Estimation of Silicon Fluoride. 



f erred to the decomposition flask through a funnel with a short 

 neck. To the material were added fifteen times its weight of 

 ignited quartz sand and 50 cm3 of sulphuric acid which had been 

 previously heated strongly and cooled in a desiccator. To an 

 iron plate supporting the decomposition flask, heat was applied 

 by a burner and regulated so that a flask of sulphuric acid 

 placed where it received the same amount of heat as the 

 decomposition flask should have a temperature of between 

 150° and 160°. During the heating a slow current of air was 

 passed through the apparatus. In the reaction in the decom- 

 position flask hydrofluoric acid was generated which acting on 

 the silica formed silicon fluoride. In the absorption tubes 

 silicon fluoride acted on water according to the following 

 equation : 



3SiF 4 + 4H a O = 2H 2 SiF 6 + Si0 4 H 4 



In the presence of potassium chloride and alcohol the fluosil- 

 icic acid was precipitated as potassium fluosilicate, and a corre- 

 sponding amount of hydrochloric acid set free. 



HJSiF. + KCl 



K 2 SiF 6 + 2HCl. 



The hydrochloric acid was then titrated with a standard 

 potassium hydroxide solution, using cochineal as an indicator. 

 A series of experiments, carried out in the manner described, 

 was made with ordinary pulverized fluorite. The heating was 

 continued in every case above the time limit of two hours. 

 All gas bubbles had disappeared from the acid mixture, which 

 fact, according to Fresenius* and Offerman,f shows that the 

 decomposition is complete. 



" The time required to decompose fluorite is stated by Fenfield 

 to be two hours for 0*2 to 1*0 grams ; by Fresenius two hours 

 for 0*1 gram and four hours for 1*0 gram. 









Table V. 















Theory 



Found 



Error 





CaF 2 



Silica 



KOH 



Fluorine 



Fluorine 



Fluorine 





grams. 



grams. 



cm 3 . 



Mcm3 — 



grams. 

 : 001045F.) 



grams. 



grams. 



1. 



0-5000 



7-0 



22-7 



0-2432 



0-2372 



— 00060 



2. 



0-5000 



7-0 



22-56 



0-2432 



0-2357, 



— 0-0075 



3. 



0-5000 



7-0 



22-7 



0-2432 



0-2372 



— 0-0060 



4. 



0-5000 



7-0 



23-15 



0'2432 



0-2419 



— 0-0013 



5. 



0-5000 



7-0 



22-4 



0*2432 



0*2340 



— 0-0092 



6. 



0-5000 



7-0 



21-7 



0-2432 



0-2277 



— 0155 



7. 



0-5000 



7-0 



22- 



0-2432 



0-2299 



— 0-0133 



8. 



0-5000 



7-0 



21-7 



0-2432 



0-2267 



— 0-0165 



9. 



05000 



7-0 



22-5 



0-2432 



0-2351 



— 0-0081 



* Zeitsehr. Anal. Chem., vi, 190. 



f Log. cit. 



