[mclennan-edwards] absorption SPECTRA OF MERCURY 173 



A = 3075-99 A°.U. In the emission spectrum of the spark taken 

 directly there are two Hnes close together at A = 3075-99 A°.U. while 

 in the lower photograph only one line is seen. In order to bring out 

 the absorption at this point more clearly, a series of photographs was 

 taken with gradually increasing vapour density. One of these is shown 

 in Fig. 10. The upper spectrum shows the line at A = 3075-99 A°.U. 

 to be double. In the second and third spectra the line is single and in 

 the fourth and fifth spectra a narrow dark band is seen close to and to 

 the left of the single line. An enlargement was taken of this portion 

 of the absorption spectrum and it is shown in Fig. 11. This photo- 

 graph it will be seen brings out very clearly the absorption band at 

 A = 3075-99 A°.U. 



If the absorption spectrum in Fig. 9 be examined it will be seen 

 that absorption bands are also shown at A = 2288 A°.U. and A = 2536-72 

 A°.U. These were no doubt due to the presence of mercury and 

 cadmium vapours in the tube containing the zinc vapour. As this 

 tube was a new one and had not been used previously it would seem 

 that the mercury and the cadmium must have been present in the zinc 

 as impurities. It is of interest to note this, for the zinc had been 

 purchased as being doubly distilled and specially pure. The mercury 

 vapour absorption band is also shown in Fig. 10 at A = 2536-72 A°.U. 



The zinc lines at A = 2139-3 A°.U. and A = 3075-99 A°.U. are 

 respectively the first members of the series given by n = 1-5, S — m,P 

 and n = 2, p2 — m, S in the spectrum of the zinc arc. There is there- 

 fore a j:omplete analogy in so far as the first members of these two 

 series are concerned in the absorption spectra of mercury, cadmium, 

 and zinc vapours. In the absorption spectra of cadmium and zinc 

 vapours no absorption was observed corresponding to that obtained 

 with mercury at A = 2338 A°.U. It will be remembered, however, 

 that with mercury this absorption band required high vapour density 

 to bring it out clearly. It may very well be that with cadmium and 

 with zinc vapours, the densities used were not sufficiently high to 

 produce noticeable absorption at points in their spectra corresponding 

 to the band at A = 2338 A°.U. in the mercury spectrum. 



V. Absorption Spectra of Gold and Silver Alloys. 



In the course of the experiments described above and in view of the 

 relationships which have been established above between the absorp- 

 tion spectra of mercury, cadmium and zinc vapours, it was thought 

 well to make an attempt to see if the absorption spectra of gold, 

 silver and copper vapours revealed similar relationships. Small 

 quantities of gold, of silver and of copper were in turn heated as highly 



