36 



THE DETERMINATION OF LITHIUM. 



The examination of tliese solutions was not made on the same day 

 with Nos. 1 and 2, hence a new determination of the observable limit 

 was made. Using the method as described before, the limit at tliis 

 time was found to be 0.0000168 mg of lithium instead of the 0.000019 

 found on the previous day. The determination was made by adding 

 to 17 CO of distilled water, portions of solution 3, 1 cc or 0.5 cc at a 

 time, the mixtures being examined after each addition. When 9 cc 

 of solution 3 had been added, the lithium line was observed very 

 faintly once in five trials, showing that the limit had very nearly 

 been reached. When 9.5 cc had been added, the line appeared three 

 times in four trials, which was regarded as the limit. Therefore it will 

 be seen that 17 + 9.5 = 26.5 cubic centimeters, each of which con- 

 tained the equivalent of the observed limit, that is, 0.0000168 mg of 

 lithium or 0.0004452 mg in 9.5 cc of solution 3. Hence, 1 cc of solution 

 3 contained 0.000047 mg of lithium or the 100 cc, the whole amount, 

 contained 0.0047. Wlien the blank which is equivalent to the amount 

 found in No. 2, 0.0016 mg, is subtracted from the amount found in 

 No. 3, there remains 0.0031 instead of 0.0028 mg of lithium known to 

 have been added to the original sample. In the case of solution 4, 

 10 cc of distilled water were taken and 3 cc of the solution added. 

 Observation of this mixture gave the line faintly twice out of five 

 trials. When 3.5 cc were added, the line was seen in each of the three 

 trials, from which it will be seen that 10 + 3.5 = 13.5 cubic centi- 

 meters each of which contained the observed limit of 0.0000168 mg 

 of lithium. The value of the 13.5 cc was therefore 0.000227 mg, which 

 is equivalent to the amount in 3.5 cc of solution 4. One cubic centi- 

 meter of solution 4 is therefore equivalent to 0.000065 mg and the 

 total 100 cc contained 0.0065 mg. When the blank determination 

 in No. 2 which is equivalent to 0.0016 is subtracted from the above 

 figure, there remains 0.0049 mg instead of the 0.0056 mg known to 

 have been added. These results are shown in the following tables: 



Determination of lithium added to mineral water {combined umyl alcohol and spectro- 

 scopic method). 



