72 LABORATORY GUIDE IN "BACTERIOLOGY 



Pour 96 per cent, alcohol on the cultures of B. prodigi- 

 osus, B. violaceus, and Sar. lutea. The pigment should 

 dissolve. Filter the liquids into clean test-tubes, and, 

 by adding a few drops of 5 per cent, hydrochloric acid, 

 note the change in color. Then add an excess of a 2 

 per cent, solution of sodium hydrate, and note whether 

 or not the color returns and is changed again. Then 

 pour chloroform on a culture of B. pyocyaneus. This 

 will dissolve the bluish-green pigment (pyocyanin). 

 Filter, and evaporate on the water-bath. When almost 

 dry, place a small amount on a slide, and observe the 

 small crystals of pyocyanin under the microscope. Note 

 also the aromatic odor given off by the pigment as the 

 solvent evaporates. 



