532 Prof. R. Bunsen's Spectral- Analytical Researches. 



The characteristic line of magnesium (Plate V. no. 10), 

 corresponding with Fraunhofer's line b, appears only in the 

 spark-spectrum, where, however, it is situated so near to another 

 line (75) that it is with difficulty distinguished from it. 



In order therefore to recognize magnesium, it is necessary to 

 substitute hydrogen or coal-gas for the air in which the spark 

 usually passes. The little apparatus represented in fig. 5, 

 Plate II. serves for this purpose. The glass vessel A is furnished 

 with a good caoutchouc stopper, through two holes in which pass 

 platinum wires connected with the carbon-points a } ft. These 

 wires are fused into small mercury cups. The glass tubes b and 

 c pass through two other holes in the stopper ; b is connected 

 with a Dobereiner's hydrogen-generating apparatus ; c carries 

 off the replaced air, and is stopped (when the air has all been 

 driven out of A) by an india-rubber cap. The fine wire /con- 

 ducts the current to the mercury-cup, whence it passes by the 

 small platinum connexion to the carbon point, and so returns 

 by the other wire g to the battery. 



In order to detect small traces of strontia and baryta when 

 these occur (as is often the case in mineral waters and rocks) 

 mixed with a large amount of lime, the bases are converted into 

 nitrates and digested with small quantities of absolute alcohol. 

 The small quantities of strontium and barium nitrates which 

 remain, or which precipitate after some hours, are collected upon 

 a very small filter and washed with alcohol ; the filter is then 

 surrounded by an exceedingly fine platinum wire, and burned in 

 the upper oxidation zone ; the ash is treated with a drop of hydro- 

 chloric acid, which is applied by means of a capillary tube; and 

 the chlorides thus formed are examined in the flame-spectrum. 

 If, in addition to the sodium-line, the spectrum of strontium is 

 alone visible, the substance on the wire must be repeatedly 

 heated and moistened with hydrochloric acid ; the barium-spec- 

 trum is then seen, if the minutest trace of that metal be present. 



Small traces of calcium and strontium may be detected in 

 barium minerals by digesting the three bases, previously con- 

 verted into chlorides, with the smallest possible quantity of 

 absolute alcohol and evaporating the liquid. The residue, which 

 is sometimes scarcely visible, is taken up by a slip of filter- 

 paper; the paper is burned on a platinum wire, and the ash, 

 while being repeatedly heated and moistened with hydrochloric 

 acid, is examined in the flame-spectrum. 



If it be wished to detect minute traces of calcium and barium 

 in strontium minerals, this may be effected by treating the 

 chlorides with cold and then with hot alcohol. Calcium is 

 found in the first, strontium in the later, and barium in the 

 last washings. 



