34 THE DETERMINATION OP LITHIUM, 



desire or expectation has been noted on the visibiUty of the lithium 

 line and so no special effort has been made to keep him in ignorance. 

 There has been an attempt to make the dilutions such that the 

 relations could not be readily calculated, so that each determination 

 of limiting concentration was independent of the others on the 

 same solution. 



Wliile working at determinations with the spectroscope the element 

 of fatigue enters as Jones ^ observed and the eye may become less 

 sensitive. On the other "hand, up to a certain time it is quite likely 

 that the eye becomes more sensitive with practice. If a complete 

 determination could be carried out with trials at only six or seven 

 dilutions as given by Abati,^ it is not likely at any time that the 

 condition of the observer would enter very largely into the results, 

 but it usually requires a number of trials to come anywhere near the 

 proper dilutions where tJie final trials may be made. The sugges- 

 tions given in the following description of the method should therefore 

 be carefully observed. 



To show "what results could be obtained by the method outlined, 

 four samples were taken through the regular procedure for the 

 determination of lithium when present in small quantities; that is, 

 the silica, sulphates, iron, aluminum, calcium, and magnesium were 

 removed in the usual way and the mixed alkali chlorids were extracted 

 with amyl alcohol and the extracted residue converted into sulphates. 

 No. 1 was 250 cc of the laboratory distilled water. No. 2 was 250 cc 

 of a mineral water at hand in the laboratory containing chiefly cal- 

 cium sulphate with small amounts of sodium and potassium and a 

 very small amount of lithium. No. 3 was 250 cc of the same water as 

 No. 2 to which was added 0.0028 mg of lithium as sulphate. No. 4 

 was 250 cc of the same water as No. 2 with 0,0056 mg of lithium as 

 sulphate added. 



The usual procedure in making a complete analysis was carried 

 out and the sulphates of lithium, sodium, and potassium were dis- 

 solved in definite quantities of water. The ordinary chemicals in use 

 in the laboratory were employed in the various separations. It was 

 known that these chemicals are frequently contaminated with very 

 small quantities of lithium; in fact, it has been necessary to reject 

 samples of calcium oxid and barium hydroxid which were found to 

 contain excessive amounts of lithium. Where the lithium is present, 

 however, in only very minute traces, it is generally better to use 

 definite amounts of chemicals in making the various separations, 

 always running a blank along with the unknowns and subtracting 

 the corrections obtained in the blank, rather than to attempt to 

 obtain chemicals which are entirely free from such minute amounts of 

 lithium as can be detected by the spectroscope. 



1 Chem. News, 1876, 34 : 122. » Gaz, cMm, ital., 1906, 36 (II) : 855-60. 



