148 BACTERIOLOGICAL CHEMISTRY LESSON 



porcelain dish at 38 -5 C. in the dark : a crystalline residue 

 of pyocyanine is obtained. 



(2) To the blue chloroform solution add dilute sulphuric 

 or hydrochloric acid, drop by drop, and shake. 



When thoroughly acidified, the solution turns red. 



Allow to settle : the chloroform which sinks to the 

 bottom of the tube is clear and colourless, the 

 supernatant watery solution red. 



(3) To this upper red layer add, drop by drop, 10 per 

 cent caustic soda solution and shake. 



The blue colour reappears. 



Allow to settle : the chloroform which again sinks to 

 the bottom of the tube takes up the blue pyo- 

 cyanine, while the supernatant watery liquid 

 becomes colourless. 



(4) Expose the blue chloroform extract to sunlight. 

 It soon loses its blue tint and becomes yellowish. 



Now add caustic soda solution : the solution assumes 

 a violet tint. 



(5) Place four tubes, containing each 5 cc. of the blue 

 chloroform extract, in boxes behind coloured glass (blue, 

 green, yellow, red) and expose them to the action of direct 

 sunlight. 



Keep a fifth tube in the dark at 22 C. 



Blue light discharges the blue colour rapidly, while 

 green light preserves it best. 



In the dark also it changes slowly. 



