510 BACTERIOLOGY. 



filtered again and the concentration is continued till about 

 50 c.c. of liquid are left. 



The concentrated blue liquid is then poured gradually, 

 with constant stirring, into about 5 volumes of absolute 

 alcohol. The blue pigment is thrown down as a sticky 

 precipitate, whereas the red color remains in solution in 

 the alcohol. The precipitate is allowed to settle thorough- 

 ly; the alcoholic liquid is then decanted as much as possible 

 or it is removed by filtration. 



The sticky precipitate is then dissolved in about 50 c.c. 

 of -water and the blue pigment is again precipitated by 

 pouring the solution, as directed above, into 5 volumes of 

 strong alcohol. The alcoholic liquid is again decanted and 

 is finally drained off as much as possible. 



The mass now contains the purified blue pigment, 

 mixed with various lime salts. Inasmuch as the pigment 

 may not possess the requisite degree of sensitiveness it 

 is well to make it as sensitive as possible. For this pur- 

 pose, about 250 c.c. of water should be added to the pre- 

 cipitate and the mixture warmed on the water-bath till 

 complete solution has taken place place. Then dilute 

 H 2 SO 4 is added, drop by drop, till a portion of the liquid 

 placed in a tube and diluted has a strong red color. The 

 liquid is then boiled to expel CO 2 and alcohol. It is then 

 neutralized by adding saturated baryta water, drop by drop, 

 and stirring well. This addition of baryta is continued till 

 a few drops of the solution, placed in a test-tube and diluted 

 with water, show a clear blue liquid without a tinge of red. 

 If a drop or less of o HC1 is added to the tube it will 

 promptly change to a deep red. The liquid is now boiled 

 for a few minutes and set aside over night. The precipitate 

 t of barium and calcium salts is then removed by filtration. 

 The purified, concentrated litmus solution is then placed in 

 Billings' glass-stoppered flasks and sterilized by steam. 

 Whenever it is desired to add the litmus to sterile lactose 

 agar, glucose agar, glucose gelatin, milk, etc., it should be 



