92 Scientific Intelligence. 



SCIENTIFIC INTELLIGENCE 

 I. Chemistry and Physics. 



1. A New Process for Determining Fluorine. — Since the 

 methods that have been employed for this determination are dif- 

 ficult and often inaccurate, the new process devised by M. 

 Travers appears to be very important. He precipitates the 

 fluorine in cold solution in the form of K 2 SiF 6 and titrates the 

 washed precipitate by means of 1/5 normal K H in the pres- 

 ence of boiling water, using penolphthalein as an indicator. The 

 whole process can be carried out in glass vessels. 



The fluorine is brought into solution in the form of an alkaline 

 fluoride, then a solution of potassium silicate of known strength 

 is added in sufficient amount to furnish about double the theo- 

 retically required quantity of silica. The solution is then neu- 

 tralized with ordinary hydrochloric acid, with the use of heli- 

 anthine as an indicator, and a slight excess, about 2 cc, of the 

 acid is added. Then solid potassium chloride is added to the 

 extent of about 20% of the liquid. The precipitate is filtered 

 upon a dense filter, washed with 20% KC1 solution or with 

 50% alcohol until the washings are neutral to helianthine, and 

 then the precipitate with the filter paper is boiled with water and 

 titrated as mentioned above. Of course, the volumetric KOH 

 solution should be free from carbonate. Test analyses showed 

 excellent results with H K F 2 , and the author states that the 

 presence of boron does not interfere. It is expected that the 

 method will be useful, not only in the ordinary determination of 

 fluorine, but also in the study of compounds in which a part or 

 the whole of this element is disguised in the form of complex 

 radicals. 



It should be stated that the author has used this method suc- 

 cessfully, with a reversed precipitation, for the determination of 

 silica. This process was carried out in silver vessels, and, while 

 this process is designed for general use in the determination of 

 silica, it is evident that it would be particularly useful for silica 

 in the presence of fluorides. — Comptes Bendus, 173, 714, 836. 



H. L. W. 



2. The Separation of the Element Chlorine into Isotopes. — 

 William D. Harkins and Anson Hayes, by the fractional dif- 

 fusion of hydrogen chloride gas through clay pipe-stems in a 

 very elaborate apparatus, have obtained heavier fractions of the 

 acid which gave for the atomic weight of chlorine values of about 

 35.49 in place of 35.46, the constant of ordinary chlorine. The 

 atomic weights were compared by getting the purified acids in 

 solution to practically the same density by dilution and careful 

 employment of the pycnometer, and then titrating the solutions 

 by the use of sodium hydroxide in weight burettes. 



