PREPARATION OF PEPTONES 2O/ 



If the sediment remains, it is a sign that more barium 

 hydroxide is to be added to the original solution. It 

 is advisable, always to work with very dilute solutions 

 of sulphuric acid and barium hydroxide, otherwise 

 one may easily overshoot the mark. 



When the solution is free from sulphuric acid and 

 baryta, we proceed to filter it through a doubled 

 sheet of folded filter paper, or, by means of a filter 

 pump, through a hardened filter impregnated with 

 animal charcoal. This process can be hastened by 

 the use of a centrifuge. The precipitate of barium 

 sulphate is stirred up with distilled water, well 

 kneaded in a mortar with water, and then filtered 

 again. It is advantageous, in order to ensure a good 

 output of peptone, to repeat this washing out with 

 cold water many times. The ninhydrin test can be 

 applied at this stage, as a test of the satisfactory 

 washing out of the precipitate. To a portion of the 

 filtrate about i c.c. of ninhydrin is added, and the 

 mixture is boiled for one minute. If the coloration 

 is faint, or even negative, then the process of washing- 

 out is discontinued. 



In the meantime, the process of concentration has 

 been begun. As solutions of peptones produce a 

 great deal of scum, the apparatus represented in 

 fig. 9 is used. The latter allows the peptone solution 

 to evaporate to dryness, at about 40 C., under 

 highly reduced pressure. The drop funnel serves the 



