500 Mr. J. Barnes on the Analysis of 
This porcelain tube is connected with a glass tube which in 
turn is connected with a large rubber tube. The mercury fills 
the. space between the porcelain and iron tubes as well as the 
porcelain, glass, and rubber tubes attached. The electric 
poles are placed as shown in the figure. By raising the 
barometer column until a drop of mercury flows over into E 
the are is started. Any further adjustments are easily carried 
out by raising or lowering the mercury column. Since all 
the joints were made air-tight the pressure could be varied by 
means of the pump. Within a few seconds after the arc is 
started the whole bulb of the receiver is covered with a layer of 
mercury thrown off from the arc, this does not penetrate into 
the neck so that the glass at B is always clear and the radiation 
from the are passes through to the slit of the spectroscope 
without loss.. The whole apparatus may be placed in a cold- 
water bath to keep the joints cool. This was found unnecessary 
with |the apparatus used, even when the arc was steadily run 
aslongasten minutes. Usually 110 volts were employed, the 
current was varied by means of a rheostat, generally 4 
amperes were used. 
With the pressure under 5 mms. the results were the same as 
those obtained with vacuum-tubes as given above. Above this 
pressure it was very difficult to obtain any components, and the 
bands were broad and hazy. This is probably due, as above, 
to pressure and the presence of a number of molecules of air. 
The results obtained with the other metallic vapours and 
gases are briefly as follows :— 
~ Cadmium.—Small pieces of metallic cadmium were enclosed 
in a Geissler tube surrounded by an asbestos jacket; when 
heated with a Bunsen flame the metal easily vapourized. 
The red line 6439 is nearly monochromatic ; there is, 
however, a weak component towards the shorter wave-lengths. 
1. Standard Component. Intensity, 1. 
2. 250° So =? aime Bs 1/5. 
The green line 5086 is composed of four components, the — 
three weaker being on the side towards the larger wave- 
lengths. 
1. Standard Component. Intensity, 1. 
2. + 04 x 105% mm: ue 1/4. 
3. + OW + ‘a 1/4. 
ae: ye | AR ent a 1/8. 
The blue line 4800 has a component on each side of the 
principal. | 3 | 
1. Standard Component. . Intensity, 1. 
ry esto 06) x 107% nam. - 1/5. 
Bein Dae s 1/4. 
