340 C. A. MACMUNN. 



aqueous extracts, as is usually the case,— due, no doubt, to 

 the different refractive index of the solvent. 



An aqueous solution gave the following readings for the 

 absorption bands : — First, A 592 to A 547, dark from A 586 

 to A 552, centre A 571 ; second, A 538 to A 516, centre A 527. 



If an excess of sulphuric acid, or of hydrochloric or 

 nitric acid, be added to such a solution, we finally, after 

 allowing the solution to stand some time, get the spectrum 

 shown in sp. 9. Certain intermediate changes of spectrum 

 take place which are not easy to map. 



Glycerine, as already said, also extracts some of the pig- 

 ment from the sponge, forming a violet sohition, and giving 

 two bands : — First, A 586 to A 550, dark from A 58r5 to 

 A 560; second, A 540 to A 518. 



Alkaline Solutions of Spongioporphyrin. — Both 

 caustic potash and caustic soda, added in small quantity to 

 alcohol or to water, are capable of extracting considerable 

 quantities of pigment. Ammoniacal alcohol, on the con- 

 trary, extracts very little; in aqueous solution it extracts 

 more. But whereas we can precipitate Spongioporphyrin 

 out of an acid solution, such as that obtained with hydro- 

 chloric acid, by means of caustic potash, we cannot do so by 

 adding an acid to the alkaline solution, or at least only to a 

 limited extent. 



If a o-reat excess of caustic alkali be added to a solution 

 of Spongioporphyrin, obtained by extracting the sponge with 

 water or alcohol containing a little caustic alkali (and giving 

 sp. 3 and 4), no further change takes place. 



Although the colour of such a solution seems red in deep 

 layers or in concentrated, solutions, yet in thin layers or in 

 weak solutions it is more of a bluish colour than the acid 

 solutions, or to be more correct it has a violet colour. 



If we take a solution got by digesting some sponge with 

 water to which a few drops of caustic soda have been added, 

 and examine a deep layer, we find the red rays between, say, 

 A 620 and A 700 are transmitted; in a less deep layer the 

 spectrum is blocked out from about A 615 to A 505, while in a 



