Hileman — Alkalimetric Estimation of Silicon Fluoride. 333 



silica thrown out of its colloidal solution by addition of the 

 electrolyte. 



The Elimination of Silicon Fluoride. 



As to the sources of error clue to imperfect elimination, and 

 collection, of silicon fluoride, we have the testimony of the 

 several investigators already quoted. The importance of using 

 the fluoride in the finest state of division, of having the sul- 

 phuric acid of highest strength, of properly absorbing the 

 vapors of sulphuric acid evolved from the decomposition flask, 

 and of using quartz for the silicon dioxide in the decomposi- 

 tion flask, have all been emphasized. Many forms of appara- 

 tus have been employed and the results have varied widely, 

 errors of from 0*0010 grams to - 0050 grams in the determina- 

 tion of fluorine by absorption and weighing of silicon fluoride 

 being not uncommon. 



At the outset of the work to be described, an investigation 

 was made as to the limit of error likely to occur in the use of 

 simple apparatus and sulphuric acid, prepared by heating to 

 the fuming point, for about a half hour. The silicon fluoride 

 evolved was estimated by absorption in an alcoholic solution of 

 potassium chloride following the method of Penfielcl,* and the 

 hydrochloric acid set free was estimated by standard potassium 

 hydroxide. 



The apparatus employed consisted of the following parts : 

 First, there was an apparatus for purifying the air current by 

 passing it through a sulphuric acid wash bottle and two large 

 drying cylinders containing fused calcium chloride at the bot- 

 tom and soda lime at the top ; second, a 100 cm3 decomposition 

 flask provided with a doubly perforated rubber stopper, 

 through which passed a glass tube from the drying cylinders 

 to the bottom of the flask, while another tube, leading from 

 this decomposition flask, was joined to a large empty U-tnbe 

 intended to condense any sulphuric acid which might be 

 carried from the decomposition flask. Third, connected with 

 the outer limb of the U-tube for condensing sulphuric acid 

 was an absorption system similar to that described by Burk.f 

 It consisted of a test tube 34 cm in length and 2 cm in diameter, 

 containing a few cm 3 of mercury into which extended a 

 delivery tube with a capillary opening. The test tube was 

 placed at an angle to diminish the pressure throughout the- 

 system. 



Before making a determination, the apparatus was first care- 

 fully dried. The absorption tube was tilled with a saturated 

 solution of potassium chloride in 50 per cent alcohol, and the 

 material to be analyzed, weighed on a watch glass, was trans- 



* Am. Chem. Jour., i. 27. 



+ Jour. Am. Chem. Soc. xxiii, 825 (1901). 



