CHITIN AMMONIA. 97 



of iron, sulphate of copper, corrosive sublimate, nitrate of mer- 

 cury, or by nitrate of silver. 



Taurin, according to the analysis of M. Dema^ay, is com- 

 posed of C 4 H 7 Az O 10 . This may be resolved into, 

 2 atoms oxalic acid, C 4 O 6 

 1 atom ammonia, . H 3 Az 



4 atoms water, . . O 4 H 4 



C 4 H 7 AzO 10 = 15-625 



This composition has been confirmed by the analysis of Dumas 

 and Pelouse.* 



CHAPTER X. 



OF CHITIN. 



THIS name (from %/7<wi>, tunica) has been given by Dr Odier 

 to the hard horny crust which forms the outer covering of many 

 insects, and in particular the elytra of the coleopterous insects.! 

 When these elytra are boiled in a solution of caustic potash, the 

 menstruum extracts albumen, a matter analogous to the extract 

 of meat, and a fatty coloured matter which is soluble in the al- 

 kali ; but insoluble in alcohol and water. What remains is chitin. 



Chitin is white and translucent. It does not melt when heat- 

 ed ; but is charred without giving out ammonia or hydrocyanic 

 acid. It is soluble in dilute sulphuric acid, and in nitric acid 

 when assisted by heat. The solution in nitric acid is not yellow, 



CHAPTER XL 



OF AMMONIA. 



AMMONIA is beyond question the most important of all the anU 

 mal bases. But its use is so indispensable to the chemist at the 

 very commencement of his investigations, that it it was necessary to 

 describe its properties while treating of the Chemistry of Inor-. 

 ganic Bodies. (Vol. i. p. 138.) 



Ann. der Pharm xxvii. 292. 



f Odier, Mem. de Mus. d'Hist, Nat. i. 35. 



