CHAP. IV.] 



B1LIRUBIN. 



317 



cipitated with alcohol, and the further purification of the separated 

 bilirubin carried out as already directed 1 . 



Physical and Chemical Characters. 



Colour and Bilirubin occurs in an amorphous and in a crystal- 



crystalline }j ne condition. In the former it presents the appear- 

 ance of an orange-coloured powder resembling sulphide 

 of antimony ; in the latter it has the colour of crystallized chromic 

 acid. Examined under the microscope, crystalline bilirubin exhibits 

 orange-coloured rhombic tables, in which the obtuse angles are often 

 rounded off. When crystallising from solutions which are not quite 

 pure (containing cholesterin, &c.) better formed crystals are obtained 

 than is the case when the solutions contain no such impurities 

 (Hoppe-Seyler 1 ). 



Bilirubin is insoluble in water, almost insoluble in 

 ether and very sparingly soluble in alcohol. It is 

 readily soluble in chloroform especially with heat ; it is likewise 

 soluble (though to a much less extent than in chloroform) in benzol, 

 carbon disulphide, amyl alcohol, and glycerin. These fluids dissolve 

 enough however to acquire a yellow or a brown red colour. Solu- 

 tions of bilirubin which contain 1 part in 500000 exhibit a percep- 

 tible yellow colour when a layer I'D cm. thick is observed (Hoppe- 

 Seyler). 



Bilirubin is readily soluble in dilute solutions of sodium, and 

 potassium hydrate and ammonia, and if the solutions be kept from 

 contact with air or with oxygen, it can be reprecipitated from them 

 by the addition of hydrochloric acid. 



It is important to notice that solutions of bilirubin in alkalies do not 

 yield the colouring matter to chloroform. A chloroformic solution of the 

 colouring matter shaken with dilute sodium or potassium hydrate is at 

 once decolourised ; on the other hand a similar alkaline solution of bilirubin 

 if acidulated and shaken with chloroform at once gives up its colouring 

 matter, which is dissolved by the chloroform and imparts to it a much less 

 brownish-yellow colour. 



Bilirubin forms compounds with bases of which several have been 

 studied. The Na-compound is obtained by precipitating a dark 

 orange solution of bilirubin in sodium hydrate by means of a 

 concentrated solution of caustic soda. 



The Ca-compound is obtained by precipitating- an ammoniacal 

 solution of bilirubin with calcium chloride. The precipitate is 

 rust-coloured, flocculent, and insoluble in water, alcohol, ether and 

 chloroform. It has the composition indicated by the formula 

 Ca^H^NjOg.Ca. When this compound is dried in vacuo over 

 sulphuric acid it is of a dark-green colour with a metallic lustre, but 

 when powdered it has a dark-brown colour. 



1 Hoppe-Seyler, Physiologische Chemie, Berlin, 1887, p. 294. 



