SPECTROSCOPIC DETERMINATION OF LITHIUM. 35 



A standard solution oi' litliium sulphate, was made containing 

 0.000113 mg per cubic centimeter of lithium. This standard soUition 

 was added a little at a time to small quantities of distilled water 

 which was known to be free from lithium, and the resulting solution 

 tested. With 15 cc of water and 1 cc and 2 cc of the above standard 

 lithium solution, the red lithium line (LiJ failed to appear in 

 two trials. With 15 cc of water and 3 cc of the standard solution, 

 the line appeared strongly once, moderately twice, was doubtful once, 

 and failed to appear twice. This was taken for the limit of con- 

 centration and was equivalent to 0.000019 mg of lithium per cubic 

 centimeter. This determination was checked by taking a larger 

 quantity of water, nameh" 25 cc, to which w^as added small amounts of 

 the standard lithium solution, a spectroscopic observation being 

 made after each addition. When to the 25 cc of water had been 

 added 5.5 cc of the standard solution, the red line was again just 

 visible, which indicated that the limit was again reached. This 

 corresponded to 0.000020 mg per cubic centimeter. The limit was 

 cliecked a third time, using 45 cc of water witli gradual additions 

 of the standard lithium solution, when it was found tliat the line 

 faintly appeared when 9 cc had been added, making the limit equiv- 

 alent to 0.000019 mg per cubic centimeter. The average of the 

 three determmations showed the limit to be for the particular con- 

 ditions under which the experiments were conducted, 0.000019 mg 

 per cubic centimeter. 



It is desirable always to make an observation of the limit at the 

 beginning and at the end of each series of determinations. Samples 

 1 and 2 were made up to a volume of 10 cc and 5 cc of the solution 

 diluted until the lithium line just disappeared. No. 1 showed the 

 line with 5 cc of the solution plus 15 cc of water. When the water 

 was increased to 20 cc, the line could no longer be detected. Five 

 cubic centimeters of No. 2 showed the line wdien 35 cc of water were 

 added, but not when 40 cc were added. In the case of No. 1, there- 

 fore, when the original 10 cc had been increased in volume to 40 cc, 

 the concentration of the lithium was the same as in the standard 

 solution when the lithium line could barely be seen. The total 

 amount of litliium. present, therefore, was 40 times the amount in 

 1 cc of the diluted standard solution, that is, 40 multiplied by 

 0.000019, equivalent to 0.0008 mg of lithium. This is the blank and 

 represents the amount of lithium obtained from the reagents used in 

 making the separations. Using the same methods of dilution, 

 No. 2 was found to contain 0.0016 mg. In the examination of these 

 two samples, the dilution method was used rather than the addition 

 of the unknown solution to a definite quantity of water until the 

 appearance of the lithium line, which is the regular method. 



The residues from Nos. 3 and 4 were dissolved in water and made 

 up to 100 cc each, and designated as solutions 3 and 4, respectively. 



