ATOMIC WEIGHT OF SILICON. 257 



liter conical Jena flask, which was provided with a particularly well 

 ground glass stopper. The volume of the sodium hydroxide solution 

 varied from 200 to 400 c.c. according to the weight of the tetrachloride 

 sample. The bulb was introduced and after thoroughly wetting the 

 walls and stopper of the flask with the alkali, the bulb was broken by 

 shaking the flask. The fog produced on breaking of the bulb appar- 

 ently disappeared after fifteen or twenty minutes, but the flask was not 

 opened for several hours, in order to make certain .that no silicon 

 tetrachloride or hydrochloric acid vapor was lost. 



The solution was always perfectly clear, although in a few instances 

 silicic acid separated in the end of the capillary of the bulb. This 

 difficulty remedied itself in some instances, for on standing the silicic 

 acid dissolved in the alkaline solution. In others, this process was 

 assisted by breaking the capillary with a blunt rod. In no case was 

 an analysis continued until all traces of such a deposit had disappeared, 

 and two experiments were abandoned because of undissolved silicic 

 acid in the capillary. 



Next the contents of the flask were diluted to 700-800 cc. and were 

 filtered through a quantitative filter into a glass-stoppered precipitat- 

 ing flask or bottle. The glass fragments were washed by decantation 

 several times and were collected on the filter, and finally the filter 

 paper was charred and the residue burned in a platinum crucible at as 

 low a temperature as possible so as to avoid the danger of volatilizing 

 alkali from the glass. 



In order to find out whether it is possible to wash the filter free from 

 sodium silicate and silicic acid, several blank experiments were carried 

 out in which a similar alkaline solution of silicon tetrachloride was 

 filtered in the same way through a quantitative filter, and after 

 thorough washing with water the filter was burned. In still other 

 experiments a weighed empty bulb similar to those used in collecting 

 the silicon tetrachloride for analysis, but open to the air, was broken 

 in the silicate solution and the glass fragments were collected and 

 determined as above. In all these experiments the ash of the paper 

 was found to be slightly in excess of the weight to be expected. 



