Analysis by Spectrum-observations. 101 



The reactions of potassium and sodium are not influenced by 

 the presence of strontium. Lithium also can be easily detected 

 in presence of strontium when the proportion of the former 

 metal is not very small. The lithium line Li a appears as an 

 intensely red sharply defined band upon a less distinct red 

 ground of the broad strontium band Sr yS. 



Calcium. 



The spectrum produced by calcium is immediately distin- 

 guished from the four spectra already considered by the very 

 characteristic bright green line Ca /3. A second no less charac- 

 teristic feature in the calcium spectrum is the intensely bright 

 orange line Ca u, lying considerably nearer to the red end of 

 the spectrum than either the sodium line Na a, or the orange 

 band of strontium Sr a. By burning a mixture consisting of 

 chloride of calcium, chlorate of potassium, and milk-sugar, a white 

 cloud is obtained which gives the reaction with as great a degree 

 of delicacy as strontium salts do under similar circumstances. 

 In this way we found that 10 000 000 of a milligramme in weight 

 of chloride of calcium can be detected with certainty. Only the 

 volatile compounds of calcium give this reaction ; the more vola- 

 tile the salt the more distinct and delicate does the reaction be- 

 come. The chloride, bromide, and iodide of calcium are in this 

 respect the best compounds. Sulphate of calcium produces the 

 spectrum, after it has become basic, very brightly and continu- 

 ously. In the same way the reaction of the carbonate becomes 

 more distinctly visible after the acid has been expelled. 



Compounds of calcium with the non-volatile acids remain in- 

 active in the flame; but if they are attacked by hydrochloric 

 acid, the reaction may be easily obtained as follows : — A few 

 milligrammes of finely powdered substance are brought on to 

 the moistened flat platinum ring in the moderately hot portion 

 of the flame, so that the powder is fritted, but not melted on to 

 the wire ; if a drop of hydrochloric acid be now allowed to fall 

 into the ring so that the greater part of the acid remains hang- 

 ing on to the wire, and if then the wire be brought into the 

 hottest part of the flame, the drop evaporates in the spheroidal 

 state without ebullition. The spectrum of the flame must be ob- 

 served during this operation ; and it will be noticed that at the 

 moment when the last particles of liquid evaporate, a bright 

 calcium spectrum appears. If the quantities of the metal pre- 

 sent are very small, the characteristic lines are only seen for a 

 moment; if larger quantities are contained, the phenomenon 

 lasts for a longer time. 



Only in the silicates which are decomposed by hydrochloric 

 acid can the calcium be thus found. In those minerals which 



