236 Photographs of tne Spark Spectra of Elementary Substances. 
Cudmium No. 17. =274:3 (Mascart).—A strong, continuous, single, sharp line, 
with a nimbus and extended. This is the longest line with Nos. 18 and 24. 
l,m, n. These lines, sharp, faint, and discontinuous, proceeding from one 
electrode only. 
Cadmium No. 18. \=257°4, (Mascart).—Strong, sharp, single, continuous, extended 
and with a nimbus. 
Cadmium No, 19, 20, and 21.—With four or five other fine discontinuous lines, 
due to the metal, occur between Nos. 18 and 22. Of these No. 19 appears to be an 
air line. 
No. 20 is rather stronger than 19, and sharp. 
No. 21 is near Nos. 22 and 23. It is not a strong line and is discontinuous. 
No. 22 is distinct, rather weaker, nearly discontinuous, with slight nimbus. 
Cudmium No. 23. A long line. A=231°8, (Mascart).—Strong with nimbus. 
o. A fine but weak and discontinuous line. This is coincident with one of 
the strong lines of indium, and it probably belongs to that element. 
p. A strong continuous line exactly similar to No. 15. 
Cadmium No, 24. =226'5, (Mascart).—Strong, continuous, extended, and with 
larger nimbus. With Nos. 17 and 18 it is one of the longest lines. 
g- This is a sharp, continuous, faint line. 
Cadmium No 25. A=221°7, (Mascart).—A faint line, scarcely continuous. 
Particulars regarding the electrodes or the specimens from which they were prepared. 
Specimens marked * were from the collection photographed by the late Dr. 
Miller, of King’s College, London. 
* Magnesium.—tThe metal supplied by the Magnesium Metal Company, Patricroft, ; 
near Manchester is of great purity, and was employed. 
* Zinc.—A sample of very pure distilled zine. 
* Cadivum.—Several specimens of cadmium were photographed, but the one the 
spectrum of which is here reproduced, was the purest. 
* Alununiwm.—By greatly lengthening the exposure, the lines of iron are made 
to appear. 
Indium.—Three specimens of this metal were examined. They were given me 
by my friend Mr. W. G. Lettsom. One was prepared by Dr. Bottger, another 
was purchased in Freiburg. Neither of these were pure. The third was 
prepared by Professor Richter, and is the one photographed here. 
Copper.—The copper was prepared by dissolving electrotype copper, which was 
found to contain only a little sulphur, in nitric acid, precipitating the oxide by 
potash, washing the oxide very thoroughly, reducing in a current of hydrogen, 
and subsequent fusion of the metal. 
* Silver.—A most carefully prepared specimen of pure silver. 
