494 KUHNE'S NEW METHOD OF PURIFYING PEPTONES. [BOOK n. 



(absolute) alcohol, when the amphopeptone is at once precipitated, 

 and soon assumes the appearance of white or greyish-white crusts. 

 These may be further purified by solution in very small quantities of 

 water and reprecipitation by absolute alcohol. They may then be 

 dried in vacuo over sulphuric acid. If it be not an 'object to obtain 

 the amphopeptone in as colourless a condition as possible, the pep- 

 tone which has been precipitated by alcohol may be dried as follows. 

 It is dissolved in water and the solution is boiled so as to drive off 

 every trace of alcohol ; it is then evaporated, in a porcelain capsule, 

 to dryness on the water bath, and may be kept in well-stoppered 

 bottles, or in sealed tubes. The so-called dry substance thus ob- 

 tained, if however further heated to 110 C., continues to lose water 

 for a long time and then the dark-coloured residue thus obtained 

 possesses the intensely hygroscopic characters first observed by 

 Kuhne: when dropped into water it dissolves with the evolution of 

 heat and with a hissing noise, in the same manner as phosphoric 

 anhydride does under the same circumstances. 



It sometimes occurs that after boiling with barium carbonate and 

 filtering, the peptone solution is found to give a precipitate with 

 dilute sulphuric acid, indicating the presence of barium peptone. In 

 this case the whole solution must be very cautiously treated with just 

 enough very dilute sulphuric acid as is needed exactly to precipitate 

 all the barium present, and thereafter the processes previously de- 

 scribed should be carried out. 



The experimenter cannot, however, be sure that his long and 

 tedious work has been successful, until having dissolved a sample of 

 the dry peptone finally obtained he submits the solution to the three 

 sets of precipitations which formed the essence of the whole opera- 

 tion. If ammonium sulphate produces any precipitate when added 

 (to saturation) to a boiling solution in the neutral, the alkaline, and 

 the acid, conditions, the whole of the product must be worked up de 

 novo. 



According to the Author's experience, however, if the whole of the 

 operations which have been described are carried out with thorough- 

 ness and intelligence, neither time nor material being spared, the 

 product obtained is found to be absolutely free from albumoses. He 

 has, however, found that even when the solution of amphopeptone, 

 filtered from the precipitate of barium sulphate, gives absolutely no 

 precipitate with either barium chloride or with dilute sulphuric acid, 

 a very concentrated solution of the amphopeptone ultimately ob- 

 tained is found to contain a trace of barium. It would appear there- 

 fore that peptones in solution prevent the perfect precipitation of 

 traces of barium by sulphuric acid. 



