THE PHOTOGRAPHIC SPECTRUM. 
227 
room provided with a heliostat for projecting a beam of sunlight into it, 
the following simple arrangement, 1 which requires merely an electric 
arc lamp and an ordinary laboratory spectroscope of the Bunsen type, 
may be adopted. 2 The telescope of the spectroscope is removed, and 
a beam from the + 'pole, of the arc is allowed to fall on the slit of the 
collimator. The spectrum is focussed on a fluorescent screen, then the 
slit is opened very widely. If the spectrum be a continuous one 
(which is the case if it be that of the positive pole of the electric 
arc), the coloured solution is then interposed in the path of the beam 
falling on the slit. 
The position and limits of Soret's band. — Defibrinated arterialised 
blood, diluted with from 400 to 600 volumes of distilled water, or still 
better with a similar amount of 0T per cent, solution of sodium hydrate, 
G h HK L M 
X 
Fig. 33. — The photographic spectrum of haemoglobin and oxyhemoglobin. 
furnishes solutions (containing about 1 part of oxyhemoglobin in 3000 
and 1 part in 5000 respectively) of a concentration suited for 
photographic investigations of the spectrum. With solutions of this 
strength (a stratum 1 cm. thick being placed in the path of the beam 
falling upon the slit of the collimator) Soret's band can be studied 
to perfection, though it can be well seen with solutions much more 
concentrated and much more dilute. The appearance and position of 
Soret's band in the spectrum of oxyhemoglobin are shown in Fig. 33 
along with that of reduced haemoglobin. 
Within fairly wide limits of concentration (the stratum examined 
being invariably 1 cm. wide), the limits and characters of Soret's band 
1 I employed this simple arrangement in demonstrating these bands in the violet and 
ultra-violet to members of the Internat. Physiological Congress, Bern Meeting, September 
1895. 
2 Direct vision spectroscopes cannot be used, the absorption of the ultra-violet rays being 
very great in these instruments. 
