Photographs of the Spark Spectra of Elementary Substances. 237 
Mercury.—This was a very good sample of the commercial article. It was 
digested for some time with strong sulphuric acid. The method of obtaining 
the spectrum of this element was the following :—A quill glass tube of an inch 
or so long was drawn out at one end to so fine an orifice that the mercury 
would not fall through when the tube was in a vertical position. This was 
treated as if it were a solid electrode, being separated at a convenient dis- 
tance from a small V tube filled with mercury, which was standing in a 
porcelain dish. Conducting wires were dipped into the upper and lower tubes, 
and as soon as the current passed a drop of mercury was forced through the 
hollow pointed tube, accompanied by the passage of a spark. 
* Thalliwm.—A specimen obtained by Dr. Miller from Mr. Crookes. 
Tellurium.—A. specimen purchased from Messrs. Hopkins and Williams. 
Arsenic.—A finely crystallized specimen in the Museum of the Royal College of 
Science. 
Antimony.—A. fine specimen in the Museum of the Royal College of Science. 
* Bismuth.— 
Tron.—Especially pure ribbon prepared by the late Dr. Matthiessen, kindly fur- 
nished to me by Dr. Russell. 
* Nickel.—A specimen in a sealed glass tube in the form of powder, prepared by 
Dr. Russell for determining the atomic weight of the element, and therefore 
most exceptionally pure. In order to get good electrodes the metal was fused 
by means of a jet of oxygen burning in an excess of hydrogen. A pair of 
electrodes were made out of the fused metal. 
-* Cobalt.—This also was prepared by Dr. Russell for a like purpose to the above. 
It was fused in the same manner. 
Palladium.—A purchased specimen which for some time has been in my 
possession. 
Gold.—An extremely pure specimen, prepared with great care by Mr. Sonstadt. 
It was twice precipitated from its solution by a current of sulphur dioxide, and 
was finally fused with potassic disulphate. This preparation was given to me 
by my friend Mr. Manning. 
Graphite.—This was a fragment from a beautiful specimen in the Museum of the 
Royal College of Science. 
*Tin.— 
* Lead.— 
I may here remark that the photographs which illustrate this paper are furnished 
from negatives which were produced from the originals on glass. They have thus, 
ingtransference from one vehicle to another, lost some of their delicacy of detail. 
The origmals on glass cannot be properly seen unless magnified forty-five or fifty 
six diameters. 
| These specimens were especially prepared for spectrum work. 
