166 Odier on the Chemical composition 



The manner in which this matter bums withput fusing, but 

 leaving a coal which retains the original form of the organ, also 

 serves to distinguish it. It cannot be confounded with the base of 

 gelatine which is soluble in boiling water, nor with skin which is 

 of the same nature ; and it is distinguished from coagulated albu- 

 men by the solubility of the latter in potassa. 



It was an interesting object to ascertain whether this substance, 

 whose characters as animal matter, are so peculiar, be really of 

 that nature, that is to say, whether it contain nitrogen. For this 

 purpose I burnt Chitine in a glass tube, placing litmus paper that 

 had been reddened, by an acid, at the mouth of the tube. If car- 

 bonate of ammonia be one of the products of the decomposition of 

 the elytra, it would restore the blue colour of the litmus paper. 

 But no such effect was produced, although it is well known, that 

 the smallest portion of nitrogen would form carbonate of ammonia. 

 Fearing lest I might have been deceived in this experiment by 

 some unknown cause, I repeated it several times, and always with 

 the same result. 



This character, joined to that derived from the action of nitric 

 acid, which does not turn chitine yellow, can leave no doubt of 

 its vegetable nature, that is, that it contains no nitrogen. Assured 

 of this, I naturally was led io seek amongst vegetable substances, 

 the one most allied to Chitine. Lignin (woody fibre) is the only 

 proximate vegetable principle which can be compared with it. It 

 is in fact, the only body, I think, which burns without swelling 

 up, and whose coal retains the form of the original substance. 



It is very remarkable that we should thus find in the frame work 

 of insects, the same substance that forms that of vegetables, or 

 which at least approaches it in many of its characters. This fact 

 will serve to confirm the opinion that nitrogen is not an essential 

 character of animal substances. 



We have now, therefore, certainly attained the knowledge of a 

 peculiar, very singular matter, which forms the base of the ely- 

 tra of insects, and is distinguished by the following characters. 

 It is insoluble in potassa ; 



Soluble in sulphuric acid, «?ith the assistance of heat ; 

 Does not become yellow by nitric acid ; 



