98 Professors Kirchhoff and Bunsen on Chemical 



somewhat greater volatility of the lithium salt, the sodium 

 reaction lasts longer than that of the other metal. In those 

 cases, therefore, in which small quantities of lithium have to be 

 detected in presence of large quantities of sodium salt, the bead 

 must be brought into the flame whilst the observer is looking 

 through the telescope. The lithium lines are often only seen 

 during a few moments amongst the first products of the volati- 

 lization. 



In the production of lithium salts on the large scale, in the 

 proper choice of a raw material, and in the arrangement of 

 suitable methods of separation, this spectrum-analysis affords 

 most valuable aid. Thus it is only necessary to place a drop 

 of mother-liquor from any mineral spring in the flame and to 

 observe the spectrum produced, in order to show that in many of 

 these waste products a rich and hitherto unheeded source of 

 lithium salts exists. In the same way during the course of the 

 preparation any loss of lithium in the collateral products and 

 residues can be easily traced, and thus more convenient and 

 economical methods of preparation may be found to replace 

 those at present employed*. 



Potassium. 



The volatile potassium compounds give, when placed in the 

 flame, a widely extended continuous spectrum, which contains 

 only two characteristic lines, namely, one line, Ka a, in the 

 outermost red approaching the ultra-red rays, exactly coinciding 

 with the dark line A of the solar spectrum, and a second line, 

 Ka /3, situated far in the violet rays towards the other end of 

 the spectrum, and also identical with a particular dark line 

 observed by Fraunhofer. A very indistinct line coincWing 

 with Fraunhofer's line B, which, however, is only seen when 

 the light is very intense, is not by any means so characteristic. 

 The violet line is somewhat pale, but can be used almost as 

 well as the red line for the detection of potassium. Owing to 

 the position of these two lines, both situated near the limit at 

 which our eyes cease to be sensitive to the rays, this reaction 

 for potassium is not so delicate as the reaction for the two 

 metals already mentioned. The reaction became visible in the 

 air of our room when 1 gramme of chlorate of potassium 

 mixed with milk-sugar was burnt. In this way, therefore, the 



* We obtained by such an improved method from two jars (about 4 

 litres) of a mother-liquor from a mineral spring, which by evaporation with 

 sulphuric acid gave l**2of residue, half an ounce of carbonate of lithion of 

 the purity of the commercial, the cost of which is about 140 florins the 

 pound. A great number of other mineral-spring mother-liquors which we 

 examined showed a similar richness in compounds of lithium. 



