468 E. RAY LANKESTER. 



the lower charts two records are given of the absorption of two different 

 thicknesses (respectively 2 millimetres and 5 millimetres) of a carefully 

 neutralised alcoholic solution of Chsetopterin. (For further details and the 

 comparison of the observed absorption of the smaller thickness of solution 

 with the theoretical value calculated from that given by the greater thickness, 

 the reader is referred to the text.) 



PLATE 37. 



Charts prepared by Dr. Engelmann of the observed absorption of the 

 spectrum by acidulated, alkaline, and neutralised alcoholic solutions of Bonelliu. 

 Two thicknesses of each solution were made use of, and their absorption re- 

 corded. See explanation of Plate 36 and the fuller statements in the text. 



