Precipitated as Thorium Fluoride. 375 



very tedious and troublesome matter. It has been found, 

 however, that the difficulty may be obviated, at least for 

 solutions of moderate dilution, by the simple procedure 

 to be described. In this procedure, a small measured 

 amount of the fluoride solution was made barely acid to 

 litmus with acetic, nitric, or sulphuric acid and then 

 added drop by drop, with stirring*, to a small measured 

 amount (a few cm 3 ) of the standard thorium nitrate 

 solution (10 grms. of the hydrous nitrate in one liter) 

 until a distinct turbidity was produced. Under the con- 

 ditions of dilution described the development of the dis- 

 tinct turbidity, which marks the beginning of immediate 

 precipitation, indicated a relation between the thorium 

 nitrate and the fluoride which was sufficiently definite to 

 serve as a basis for the easy calculation of the amount of 

 thorium nitrate required for complete precipitation of 

 the fluoride. The determinations of Table III show that 

 turbidity is produced upon addition of the fluoride solu- 

 tion to the excess of thorium nitrate solution when the 

 amount of the latter is about two and a half times as 

 much as would be required theoretically for the precipi- 

 tation of the amount of fluoride used and this amount is 

 about twice as much as may be used with safety if the 

 precipitation is to be complete. 









Table III, 







The Point < 



Df Incipient Precipitation when the Fluoride 





is added to 



an Excess of 



Thorium Nitrate. 















Ratio of 



Fluoride 



Thorium 





Th0 2 equiv- 



Th0 2 contained 



ThO, used to 



solution 



nitrate 



Water 



alent to 



in thorium 



ThO« equivalent 



N/10 



solution* 



added 



fluoride 



nitrate used 



to fluoride 



cm 3 



em 3 



cm 3 



grm. 



grm. 



grm. 



0-52 



2 







0-0036 



00094 



2-6 : 1 



0-54 



2 



2 



00037 



0-0094 



2-5 : 1 



0-80 



3 - 







0-0055 



00141 



. 2-6:1 



0-81 



3 



3 



00056 



00141 



2-5 : 1 



0-82 



3 







0-0057 



00141 



2-5 : 1 



0-83 



3 







0-0057 



00141 



2-5 : 1 



0-84 



3 







0-0058 



00141 



2-4 : 1 



1-35 



5 







00093 



00235 



2-5 : 1 



2-70 10 00186 0-0470 2-5 : 1 



* 10 grm. of the hydrous salt in 1 liter. 



According to this procedure, directions for the precipi- 

 tation of the hydrous thorium fluoride, ThF 4 .4H 2 0, from 

 a fluoride solution of unknown concentration may be sum- 

 marized as follows : 



