338 SOLID PARTS OF ANIMALS. 



When heated in the open air it behaves rather like a vege- 

 table than an animal substance. It does not melt nor swell, gives 

 out little smoke, but emits a disagreeable vegetable odour. When 

 the heat is increased it burns with flame, and leaves a greyish 

 ash having a shade of red. This ash dissolves with effervescence 

 in nitric acid, and leaves a little peroxide of iron behind. 



Gmelin distilled the pigmentum nigrum and obtained an empy- 

 reumatic oil, carbonate of ammonia, and combustible gas, and 

 water. The charcoal remaining in the retort amounted to 44-6 

 per cent, of the pigmentum nigrum distilled. This charcoal was 

 difficult to incinerate. The ashes which it left consisted of chlo- 

 ride of calcium, carbonate and phosphate of lime, and peroxide 

 of iron. *A solution of chlorine made the pigmentum nigrum 

 much paler and dissolved about the half of it, The undissolved 

 portion was rendered deep-brown, and readily dissolved by potash 

 ley. The acids precipitated it from that solution with a brown 

 colour. Fuming nitric acid dissolved the pigmentum nigrum 

 with effervescence, and the solution had a reddish brown colour, 

 was bitter, and partly precipitated yellowish brown by water and 

 an alkali. When concentrated sulphuric acid was heated with 

 pigmentum nigrum sulphurous acid was given out, and a black so- 

 lution was formed, from which water threw down brown flocks, 

 which were not so easily dissolved by potash as the unaltered 

 pigment. Boiling muriatic acid dissolved a small quantity of 

 the pigment ; the solution had a brown colour. Caustic potash 

 dissolved it slowly and incompletely at the boiling temperature; 

 the solution had a reddish brown colour and disengaged ammo- 

 nia. Muriatic acid threw down from this solution brown flocks, 

 soluble in cold potash ley and in ammonia. The pigmentum 

 nigrum is insoluble in both fixed and volatile oils.* 



In short, the properties of the pigmentum nigrum of the eye 

 are very similar to those of the dark matter which constitutes the 

 ink of the cuttle-fish. 



Dr Scherer subjected it to an ultimate analysis.f He obtained, 



Carbon, . 58-21 



Hydrogen, . 5-92 



Azote, . 13-77 



Oxygen, . 22-10 



100-00 

 * Berzelius, Traite de Chimie, vii. 451. f Ann. der Pharm. xl. 63. 



