268 Hartiry—The Action of Heat on the Absorption Spectra and 
It was very difficult to make even approximately accurate observations owing 
to the variations in the illuminations of the field of view in the spectroscope, 
for, as the light diminished in quantity and intensity, the eye became accustomed 
to the subdued light, and the cross-wires in the eye-piece became visible in posi- 
tions where previously they had been obscured. All measurements, therefore, 
must be regarded merely as approximations. They serve to show that the change 
is measureable, and to what extent it occurs under different conditions. 
The variations in the spectrum of this solution were very striking, as already 
mentioned in a preliminary note.* Except by reference to the drawings, no idea 
of them can be formed. : 
Occasionally an obscure band of red rays was seen to flash down the dark part 
of the spectrum about wave-length 720. 
In the preparation of the solution of cobalt chloride 10 grs. of CoCl,6H,O 
were covered with 5 ¢.c. of water at 16°-4, which caused the temperature to fall to 
12°-0, after which it rose. The liquid was allowed to stand until saturated with 
the salt, but was poured off after a lapse of 48 hours, and the crystals drained 
from adhering solution and weighed. 8 grs. of CoCl,;6H,O were found to have 
dissolved in 5 c.c. of water at 16° C., and the solution measured 9°2 c.e. 
The photographed Spectra of Cobalt Chloride Solutions. 
The general results of the examination of the cobalt chloride solutions have 
been confirmed, as far as practicable, by means of photography, using Cadett and 
Neall’s Spectrum plates. The results vary a little from those made by the eye 
observations for these reasons: first, the source of illumination was sunlight ; 
secondly, the sensitiveness of the eye is not the same as that of the photographic 
film; and thirdly, it may be pointed out that exactly the same thickness of liquid, 
or, in other words, the same part of the wedge-shaped cell, was not always 
examined, though, as nearly as could be judged by the eye, this was adhered to. 
Then again the extinction of ight which rendered the cross-wires visible was 
judged by the eye, but no such means of measuring could be applied to the photo- 
graphic method. 
It was not found practicable to maintain a strictly stationary temperature, 
because the necessary heating apparatus could not be interposed between the con- 
densing lens and the slit. The instrument was a spectrograph with four quartz 
prisms, the same that had been previously used in photographing the spectra of 
the Bessemer flame, and is figured and described in the Journal of the Iron and 
Steel Institute, No. II., for 1895. 
It was adjusted and focussed so as to give special distinctness and sharpness to 
the red end of the spectrum. 
* Proc. Roy. Soc., vol. xxii., p. 241. 
