ON SPONGTOPORPHYRTN. 343 



Polyopogon is extremely unstable. This was observed by 

 Mr. Kirkpatrick, who states in his notes: " {a) HNO3 bleaches 

 instantly; (&) KHO turns colour from pui-ple to brick-red; 

 (c) KHO and NHo added to a bleached piece of sponge partly 

 restore colour; (d) the alkaline (KHO) brick-red colouring- 

 matter is bleached by HNO3, and again restored by adding 

 more KHO; (e) colouring matter insoluble in benzol." 



In contrast to the pigment of Suberites, that of Polyo- 

 pogon disappears at once when portions of sponge ai*e put 

 into water acidulated with hydrochloric acid. On putting 

 portions into water to which a little caustic potash had been 

 added, the colour changed to brick-red. The sponge itself 

 has a kind of dull violet-brown colour quite diiferent from that 

 of Suberites, and in the sponge itself and in its solutions I 

 could not see any absorption bands. 



Both water and glycerine take up some pigment from 

 Polyopogon. The aqueous solution has a pale violet tint, 

 and shows no bands. Nor do any appear on treatment with 

 ammonium sulphide. The same remarks apply to the glyce- 

 rine extract. 



Portions of sponge clarified by means of glycerine and 

 examined with an Abbe condenser and open diaphragm, and 

 microspectroscope, show no bands before or after adding 

 ammonium sulphide. 



This pigment may be isolated by taking an acidulated 

 alcoholic solution, which has a faint yellowish tint, and 

 shows no bands, and adding a little caustic potash solution. 

 The almost colourless fluid gets reddish. The precipitate 

 may then be filtered off and further purified. 



If a bit of sponge be taken which has lost its colour under 

 the influence of alcohol acidulated with hydrochloric acid, 

 and be washed free from acid and then be placed in water 

 containing a little caustic potash, the sponge becomes reddish 

 brown. If now the alkali be Avashed off, and a little water to 

 which hydrochloric acid has been added is poured on the bit 

 of sponge, the latter is again almost decolourised. It has 

 now, however, a faint greenish tinge. On again washing and 



VOL. 43, PART 2. NEW SEKIKS, A A 



