206 
PROFESSOR W. N. HARTLEY OX 
clean iridiam was heated in the flame for seventy minutes and the spectrum 
photographed. 
When the wire was at its highest temperature the flame assumed a peculiar bluish 
colour and the wire became very thin. The spectrum obtained proved to be similar 
to that previously obtained from pure silica. 
A second spectrum was taken on the same plate, a little silica being placed on the 
loop of iridium. The spectrum was similar to the first, the lines being the same, but 
\veaker, as the silica acted as a glaze and protected the wire. 
It is perfectly evident that this metal was to some extent vaporized in the flame, 
and that the vapour emits a line spectrum. 
The following are measurements of the lines photographed :— 
\. 
X. 
4386 
3599 
3479 
42.56 
3812 
3596 
3475 
3965 
3772 
3533-5 
3464 
3987 
3705 
3511-5 
3436-4 
3860 
3696 
3.508-7 
3400 
3815 
3663 
3484-3 
3328 
These lines have not yet been identified, but they are suspected to be due to 
osmium. 
A small strip of pure iridium, for which I am indebted to Mr. George Matthey, 
F.R.S., was exposed to the flame for three hours and a quarter, and a line spectrum 
with a small portion of a continuous spectrum was photographed. Undoubtedly the 
iridium was volatilized, for it lost weight to the extent of 0'082G grm., and the end 
was worn away by the flame impinging upon it. The spectrum was very Aveak, the 
lines Avere not those referred to above, and it is suspected that some of them at least 
are due to a gaseous spectrum, or possibly to a series of the lines belonging to the 
spectrum attributed to Avater vapour Avhich have not previously been observed. 
The fact that iridium is slightly volatile has undoubtedly been proA^ed, but if the 
metal is pure it may be used adA^antageously for the purpose of supporting irreducible 
oxides in the oxy-hydrogen blow-pipe flame. 
ATAVAlINHLAr. 
When the metal, in the form of foil, is burnt in the oxy-hydrogen bloAV-pipe, it 
elves a spectrum Avhich is continuous, but in AA'hich some fsAV lines or narroAA' bands 
are visible. There can be little doubt that these are due to impurities, principally 
iron. With the exception of three the lines are all very faint. The measurements, 
Avhlch are only approximations, oAAung to the indefinite character of the lines, are the 
