608 PEOFESSOE STOKES ON THE LONG SPECTETJTVI OE ELECTEIC LIGHT. 
dered, I prefer tin — the electrodes (or one of them at least) being broad, for a reason 
which will be mentioned presently. Tin, indeed, is weak in the most refrangible 
region, though after a long interval of weakness it shows one pretty strong line between 
the 2nd and 3rd of the strong aluminium lines ; but with these substances the distinctive 
features of the absorption hardly ever occur so late. For combined strength and con- 
tinuity, copper answers well for the highly refrangible region in which tin is weak; 
while mercury, which may be employed in the form of amalgamated zinc, is the richest 
metal for the invisible region just beyond the visible spectrum ; but I have employed tin 
almost exclusively. 
The following figure gives the bands of absorption observed in solutions of several 
Fig. 2. 
Principal lines of zinc 
Strychnine, in dilute sulphuric acid 
Brucine, in dilute sulpliuric acid . . . 
Morphine, in dilute sulphuric acid 
Codeine, in dilute sulphuric acid . . . 
Narcotine, in dilute sulphuric acid 
Narceine, in dilute sulphuric acid ... 
Papaverine, in dilute sulphuric acid 
Caffeine, in dilute srdphuric acid . . . 
Corydaline, in dilute sulphuric acid 
Pipeline, in alcohol 
^sculine, in dilute ammonia 
Phlorizine, in dilute ammonia 
Phlorizine, in dilute sulphuric acid 
Salicine, in water 
Arbutine, in water 
alkaloids and glucosides. The bold lines of zinc are given as points of reference ; but 
the observations were made with electrodes of tin. The border on the left is the limit 
of the red light visible on a screen. 
