JO6 PREPARATION OF PEPTONES 



precipitate, either with barium hydroxide solution or 

 with sulphuric acid. In the test with barium hydroxide 

 it may happen, that a precipitate appears, even though 

 no more sulphuric acid is present. These are barium 

 salts of peptones, which separate out. They can be 

 dissolved in nitric acid, while barium sulphate is 

 insoluble in this. 



Neutralization is carried out in such a way, as to 

 calculate the quantity of barium hydroxide necessary, 

 by the amount of sulphuric acid used. The barium 

 hydroxide is best added in the solid form, and is well 

 stirred until the action is complete. The neutral- 

 ization of the sulphuric acid is first tested by means 

 of litmus paper. Finally, small samples are filtered 

 through a small funnel, 21 and then one sample is 

 tested with barium hydroxide, 22 and another with 

 sulphuric acid. If, in the first case, the solution 

 becomes turbid, or precipitates are formed, then nitric 

 acid is added, and the solution is slightly warmed. 



21 If there be a centrifuge at one's disposal, then we recom- 

 mend centrifuging samples of the mixture. In this way a 

 clear solution is obtained immediately without any loss of 

 material. 



22 For testing purposes an aqueous solution of barium 



chloride gives better results than barium hydroxide, because 

 the baryta water becomes turbid, owing to its affinity for 

 carbonic acid, with consequent formation of barium carbonate. 

 When using the above solution, the sample employed must 

 never be returned to the original solution, but must be thrown 

 away. 



