Hileman — Alkalimetric Estimation of Silicon Fluoride. 337 



to about three times the weight of the fluorine present, is 

 transferred to the decomposition flask. Next, enough sul- 

 phuric acid to seal the delivery tube from the side neck flask 

 is introduced into the Yoit flask. The two flasks are then 

 tilted so that the acid should moisten the connecting tubes to 

 the bend. About 40 cm3 of sulphuric acid and several capillary 

 tubes l mm in diameter sealed l cm from an open end and at the 

 other end* to prevent bumping, are added to the decomposi- 

 tion flask, and the stopper quickly replaced and sealed with a 

 drop of sulphuric acid. The acid used above had been boiled 

 for half an hour and a current of dry air passed through on 

 cooling. A thin strip of asbestus is wrapped about the neck of 

 'the flask, and the stop-cock having been closed, the bulb is 

 heated in a radiator whose top is covered with a sheet of 

 asbestus matting. 



Tvnen heat is applied in the process, bubbles of gas are given 

 off, the solid material rises to the surface, and during the 

 course of the heating an oily film gathers on the upper part 

 of the flask and in the delivery tube. On boiling, this film is 

 replaced by a white deposit which recedes before the acid 

 vapors. The success of the determination depends, as was 

 found, on the removal of this deposit. When the acid vapors 

 have penetrated the length of the tube leaving it clear or 

 translucent, the decomposition is complete, and the stop-cock 

 having been opened, the side neck flask is cooled to about 75°. 

 A current of purified air is drawn through the apparatus, 

 slowly at first and then more rapidly. About six liters are 

 necessary to remove the last trace of silicon fluoride. 



Daniels'^ suggestion that the deposit mentioned above is a 

 polymer of SiF 4 appears unwarranted. It seems more proba- 

 ble that this is a product of partial hydrolysis of silicon flu- 

 oride by the action of water generated in the action of 

 sulphuric acide on the fluoride, as suggested above, the process 

 of forming and hydrolyzing silicon fluoride being repeated until 

 the water is finally absorbed in the cold acid of the Yoit flask. 



If it happens that the acid mixture bumps before the decom- 

 position is complete, some of the deposit may become dis- 

 lodged from the tube and remain undecomposed in the Yoit 

 flask. Bumping also renders it difficult to boil the acid vapors 

 through the delivery tube. On this account the tube between 

 the two flasks should be as short as is practicable. Unsatis- 

 factory results were obtained when the tube was about one- 

 half longer than the dimensions given above. If the acid tends 

 to suck back from the Yoit flask, it is arrested by opening the 

 stop-cock for a moment to relieve the vacuum. If, at this point 

 of the experiment, the pressure regulator should not be 

 adjusted properly, acid vapors would be drawn through the 



* Scudder. J. Am. Chem. Soc, xxv, p. 113. 

 f Zeitschr. Auorg. Chem. xxxviii, 257. 



