1889.] Photographs of the red end of the Spectrum. 155 



dissolves and when dried forms a dark purple powder, known as Alizarin 

 Blue S or Anthracene Blue. In this form it is readily soluble in water, 

 the solution in distilled water being at first of a brownish orange colour, 

 turning blue on exposure to air. By keeping a few days the colour forms 

 a floculent precipitate, and is then only partially soluble in dilute 

 ammonia. 



Examined with the spectroscope solutions of the dye do not give a 

 very marked absorption spectrum. 



The plain orange solution of Alizarin S in distilled water absorbs the 

 violet, blue and green up to about b. 



The greenish-blue ammoniacal solution absorbs the red, orange and 

 yellow very strongly down to about D ^ E., with a general lowering all 

 over the spectrum. There are no distinct absorption bands. I do not 

 find any marked difference in the absorption spectra of the ammoniacal 

 watery solution of three samples of the dye in my possession. 



I. Alizarin Blue paste, from the Elberfeld Factory, formerly F. 

 Baeyer and Co. 



II. Alizarin Blue S, from the Badische Anilin and Soda Fabrik. 



III. Anthracene Blue, from Dr. Schuchai'dt of Gorlitz. 



In his work " Practische Spectral Analyse Irdischer Stqffe," Dr. H. W. 

 Vogel gives two very different absorption spectra for the ammoniacal 

 watery solutions of pure alizarin blue and of Anthracene Blue, also ob- 

 tained from Schuchardt ; the first agrees with my observations — but the 

 second, which shows maximum absorption between D and E, does not. 



The photographs now exhibited have for the most part been taken 

 with No. II, but others have been taken with Nbs. I and III. Tho 

 effect of all of them seems very similar, but further trials are required 

 to ascertain which is best. 



The plates I have used have been the ordinary commercial celatine 

 dry plates. Wratten's ' Instantaneous ' have perhaps given me the 

 best results, but the ' Ordinary ' have also proved wonderfully sensitive 

 under the action of the dye. The plates are stained by bathino- them 

 for one or two minutes in a solution of the dye in distilled water in the 

 proportion of 1 part of the dye to 10,000 parts of distilled water with 

 l°/o of strong solution of ammonia added. The solution has at first a 

 strong greenish tint, but this soon changes to blue and I have noticed 

 that after a time it again takes a gTeener tint. 



With a small spectrograph on Dr. Vogel's principle, consisting of a 

 Browning pocket spectroscope attached to a camera in front of a sino-Je 

 element of a small Steinheil aplanatic lens (the addition of this lens is 

 I find, a great improvement to the instrument as originally proposed 

 by Dr. Vogel) the spectrum obtained on the stained plates shows very 



