338 Hileman — Alkalimetric Estimation -of Silicon Fluoride. 



apparatus into the absorption tube. The decomposition is 

 ended in fifteen to forty minutes. The delivery tube is 

 washed and the absorption solution transferred to a flask and 

 titrated with sodium hydroxide* from an alkali burette, with 

 phenolphthalein as an indicator, according to the method of 

 Offerman, the third method referred to above. 



H 2 SiF 6 + 6NaOH = 6NaF + Si(OH) 4 + 2H a O 

 The following series of results was obtained according to 

 the method outlined above. 









Table VIII. 















Theory 



Found 



Error 





CaF 2 



Quartz 



Na 3 OH 



Fluorine 



Fluorine 



Fluorine 





grams. 



grams. 



cm. 



(l Cm 3 = 



grms. 

 3-005123F.) 



grms. 



grms. 



1. 



0*3000 



0-4 



28-2 



0-1459 



0-1444 



— 0-0015 



2. 



0-3000 



0-4 



28-35 



0-1459 



0-1452 



— 0-0007 



3. 



0-3000 



0-4 



28-34 



0-1459 



0-1451 



— 0-0008 



4. 



0-3000 



0-4 



23-5 



0-1215 



0-1203 



— 0-0012 



5. 



0-3000 



0-4 



28 3 . 



0-1459 



0-1419 



—o-ooio 



6. 



0-3000 

 NaF. 



0-4 



28-37 



0-1459 



0-1453 



— -0006 



7. 



0-3000 



0-4 



26-2 



0-1356 



0-1342 



— 0-0012 



8. 



0'3000 



0-4 



26-44 



0-1356 



01355 



—o-oooi 



9. 



0-3000 



0-4 



26-46 



0-1356 



0-1356 



— -oooo 



to. 



0-3000 



0-4 



26-3 



0-1356 



0-1347 



— 0-0009- 



11. 



0-300O 



0-4 



26-34 



0-1356 



0-1349 



— 0-0007 



12. 



0-3000 



0-4 

 Ignited 



26-3 



0-1356 



0-1347 



— 0-0009 







Silicic acid 









13. 



'0-3000 



0-4 

 Quartz 



26-29 



0-1356 



0-1346 



-o-ooio 



14. 



0-3000 



0-4 



26-3 



0-1356 



0*1347 



— 0-0009 





Ca 



= 40-1 



Na = 23-04 F-L9 



( error 



— 0-0008) 



With the apparatus described above, in which the sulphuric 

 acid in the decomposition flask may be boiled, the silicon 

 fluoride formed passes rapidly to the absorption system, other 

 products of partial hydrolysis of silicon fluoride formed in the 

 flask or tube are ultimately reconverted to silicon fluoride, and 

 regular results of a fair degree of accuracy are obtained. In 

 all the experiments above except (6) and (14) phosphorus pen- 

 toxide, about 2-0 grams was introduced into the decomposition 

 flask, the purpose being to retain water formed in the reaction. 

 The results of the experiments specifically mentioned show, 

 however, that phosphorus pentoxide in the flask is not essential. 

 In three blank experiments, where the acid in the decom- 

 position flask was heated to boiling, amounts of acid in each 

 case equivalent to 0*0002 grams of fluorine were found in the 

 absorption solution ; the above results therefore are subject to 

 this trifling error. 



*Kuster, Zeitschr. Anorg. Chem. xli, 475. 



