OF THE SPONGIAD.E. 65 



due to the traces of sesquioxide of iron present in the 

 fibres, and the difference in shade is simply caused by the 

 greater or less preponderance of that metal. 



"Although I have not been able to obtain fibroin in 

 a state of chemical purity, I would state that, to my 

 knowledge, there is no vegetable principle which behaves 

 itself towards reagents in a manner similar to that shown 

 by the substance of silk, sponge, &c. 



" Mulder and Crookewit's analyses show silk and sponge 

 scarcely to differ in composition. 



Fibroin 

 from Silk. 



Carbon 48'5 



Hydrogen . . Pr5 



Nitrogen . . 17'3 



Oxygen 1 



Sulphur } . . . 27'7 



&c. &c. J 



100-0 



Fibroin from 



Sponges. 



Carbon . 46'5 to 4S'5 



Hydrogen . . 6'3 Cv3 



Nitrogen . . lf,-l Ifrl 



Oxygen 

 Sulphur 

 Phosphorus 

 Iodine 



31-1 29-1 



100-0 100-0 



Schlossbcrger has recently expressed his doubts of the 

 identity of composition of these bodies, from the cir- 

 cumstance that silk is readily soluble in strong ammonia, 

 saturated with oxide of copper, whilst sponge is scarcely, or 

 not at all, affected by long maceration. My own expe- 

 riments prove the same fact, yet it is not impossible that 

 the minute quantities of iodine, phosphorus, and sulphur 

 present in sponge may modify the solubility of the 

 fibre. 



" Under the supposition that a resinous gum might act 

 as a protection, portions of sponge were boiled in benzol, 

 ether, and alcohol, but these solvents did not modify the 

 characters in any noticeable degree. 



" I consider, however, that this difference between 

 sponge and silk in no wise affects the question of the 

 former substance being a product of the animal kingdom, 

 which the other experiments, I think, satisfactorily 

 prove." 



In considering the results of these analyses with a view 



5 



