PROPERTIES AND METHODS OF IDENTIFICATION 233 



being a ready solvent. Benzene <li>snlvr.- ihc pmv crystals much more 

 easily and chloroform and carbon disultidc with great ease. Kohl 

 (1902e) gives the specific rotation of carotin in chloroform as 

 g D = 30.17, but this property is not mentioned by other investi- 

 gators. 



Carotin crystals, and even the amorphous pigment, if free from 

 lipoids, dissolve in concentrated H..SO with an indigo blue color, from 

 which the pigment precipitates as green flakes on dilution. A similar 

 color reaction is given by concentrated HN0 3 , dry sulphurous acid 

 and by thymol and phenol containing concentrated HC1. The crys- 

 tals also give a transient blue color with bromine water and with 

 bromine vapor. With ferric chloride a deep green color is given. 

 This reaction was explained in a previous paragraph. The color 

 reaction of carotin with H 2 S0 4 , which is also given by the other 

 carotinoids, is regarded by many as a specific reaction for these 

 pigments. There is no justification for this idea, which may easily 

 lead to erroneous conclusions, because this reaction is given by a 

 large number of organic compounds, especially by certain quinones of 

 the aromatic group. 



The crystals of carotin readily oxidize, whereby the crystals bleach 

 entirely. The original melting point of 167.5-168 C. falls and the 

 pigment changes markedly in properties. A number of investigators 

 have reported that the bleached pigment shows the color reactions 

 of cholesterol, but Willstatter and Mieg and Euler and Nordenson were 

 unable to confirm this. The amount of oxygen which carotin is ca- 

 pable of taking up during the oxidation has been variously reported, 

 Arnaud reporting 21 to 24 per cent, Kohl as high as 37.87 per cent. 

 Willstatter and Mieg obtained a maximum of 34.3 per cent, cor- 

 responding to 11 atoms of oxygen. Willstatter and Escher (1910) ob- 

 tained an oxidized product in dry oxygen corresponding to nearly 12 

 atoms of oxygen. They found that oxidation in a room saturated with 

 moisture gave a product with a like amount of oxygen but containing 

 2 molecules of water, in addition. The perfectly pure pigment crys- 

 tals did not oxidize readily. By placing them in a stream of pure 

 oxygen the increase in weight was only 0.3 per cent after five days. 

 After this the oxidation was more rapid, and was accompanied by the 

 violet-like odor which had been described by others for the pure pig- 

 ment. 



Carotin being an unsaturated hydrocarbon would be expected to form 

 stable halogen derivatives. Two iodides have been described, one by 



