268 Hartley — The Action of Tlcat on the Absorption Spectra and 



It was very difficult to make even apjiroximately accurate observations owing 

 to the variations in the ilhiminations 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 CoCl2"6H20 

 were covered with 5 c.c. of water at 16"'4, wliich caused the temperature to fall to 

 r2°'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 CoCh'GHaO were found to have 

 dissolved in 5 c.c. of water at 16° C, and the solution measured 9'2 c.c. 



The photographed Spectra of CoJjalt 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 light 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 I'ed end of the spectrum. 



* Proc. Roy. Soc, vol. xxii., p. 241. 



