G4 Prof. Roscoe on the Spectra of the Chemical Elements, 



low temperature. This influence on the mass of the temperature 

 of the incandescent gas explains perfectly why, in the spectra of 

 many metals, those lines which are the most prominent when the 

 metal is placed in the colourless gas-flame, are not the most di- 

 stinct when the spectrum of the induction-spark from the metal 

 is examined. This is most clearly seen in the case of the calcium 

 spectrum. I have found that if a wet string or a narrow tube 

 filled with water be placed in the circuit of the Leyden jar which 

 gives the spark, and if the electrodes be moistened with a solu- 

 tion of chloride of calcium, a spectrum is obtained which coin- 

 cides exactly with that seen when a chloride-of-calcium bead is 

 placed in the colourless gas-flame. Those lines appear absent 

 which are the most distinct when an entire metallic circuit is 

 employed. If the narrow column of water be replaced by a 

 column of larger sectional area and of shorter length, a spectrum 

 is produced in which both those lines which are seen in the flame 

 and those obtained by the intense spark are equally plainly 

 visible. In this experiment we see the mode in w r hich the cal- 

 cium spectrum, as given in the flame, may be converted into that 

 produced by the bright electric spark." 



I may likewise add that, in lately examining the spectrum 

 of lithium obtained by the induction-spark from a RuhmkorfPs 

 coil with one of StemheiPs prisms, Professor Clifton and I ob- 

 served the appearance of two blue lines, one of which (probably 

 the line noticed by Dr. Tyndall) we found to be coincident with 

 the common blue strontium line B, whilst the other coincided 

 with a seeond blue strontium line, which became first apparent 

 in the spark-spectrum of this metal. Whether the lines thus 

 produced in the spectra of lithium and strontium will prove to be 

 coincident when examined with a larger number of prisms and 

 with a higher magnifying power we are unable at present finally 

 to decide; but by employing three of SteinheiPs prisms, each 

 having a refracting angle of 60°, there appeared to us a slight 

 difference in refrangibility between the first blue lithium line and 

 the line Sr 8, — this difference, however, not being so large as that 

 between the two sodium lines. We hope to be able before long to 

 give a definite answer to this important and interesting question. 

 The explanation of the coincidence by possible presence of strontia 

 in the lithia, is disposed of by the fact that when the blue lines 

 are most intense no trace of the orange or red strontium lines «, 

 /3, and y can be observed. The lithium-salt which I used was the 

 sulphate, being a portion of some pure salt sent me by Professor 

 Bunsen ; the strontium-salts employed were the chloride and ni- 

 trate, and with both of these. the same coincidence was observed. 

 I remain, Gentlemen, 



Yours truly, 



Henry E. Roscoe. 



