108 Oilier on the Chemical composition 



of that time I took it out, perfectly freed from all earthy sub- 

 stances. Jn this state, the carapace is formed of laminae of a soft 

 flexible substance, with a light brown tint, laid one on the other. 

 Having well washed this substance, I dried it in order to compare 

 it with the chitine of insects. I first submitted it to the action of 

 potassa in which I boiled it for a considerable time. The carapace 

 became white, and transparent, but did not dissolve. This was 

 already a strong reason for presuming that this matter was the same 

 as that from the insects ; but the action of nitric acid, and its de- 

 composition by heat, which presented the same characters that I 

 had observed in chitine, left me no doubt as to the absolute iden- 

 tity of th* two substances. I should have been glad to have exa- 

 mined likewise the animal matter of the Mollusca, Zoophyta, &c. 

 to ascertain if it be of the same nature as that of insects and Crus- 

 tacea ; but not being able to extend my researches at present, I 

 reserve those experiments for a future season. 



Of the coloured oil contained iu the elytra. 



We have seen that the elytra of the Cockchaffer treated with 

 alcohol, left, on evaporating the liquid, a brown oil. The Crioceris 

 merdigera, treated in the same manner, alibi ds a red oil, which, 

 as M. Lassaigne informed me, is still more beautiful if the elytra 

 be treated with ether. This oil changes readily by exposure to the 

 air, and loses its red colour. Observing the relation that exists 

 between the colour of these oils, and that of the insects from 

 which they are derived, I was led to conclude that it is to them 

 they owe their colours. Many other facts of the same nature have 

 confirmed this opinion. Reading M. Robiquet's memoir on Can- 

 tharides, in the 76th vol. of the Annales de Chimie, we. find that 

 by treating Cantharides, (previously digested in water till it had 

 no farther action) with alcohol, he obtained a fine green oil, simi- 

 lar to the colour of those insects. 



We may conclude, I think, from these facts, that the colour of 

 the horny pieces of insects, is derived from an oil, coloured ac- 

 cording to the species. On examining those pieces, we observe 

 that the colour is merely superficial, their interior being coloured 

 by the brown animal matter. 



