OF THE SPONGIAD^. 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. 



Mbroinfrom 



100-0 



. 46-5 to 48-5 

 . 6-3 6-3 

 . 161 16] 



, 31-1 39-1 

 100-0 100-0 



Schlossberger 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 qaestion 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 



