APR iv.] KUHNE'S NEW METHOD OF PURIFYING PEPTONES. 493 



Separation of When the successive saturations with ammonium 

 peptones from sulphate, at a boiling temperature, have been effected, 

 ammonium the experimenter is, at last, in possession of a large 

 sulphate. quantity (perhaps a great many litres) of a cold satu- 



rated solution of ammonium sulphate containing amphopeptones. 

 As pure water dissolves, at ordinary temperatures, about 70 per cent, 

 of its weight of ammonium sulphate, it follows that each kilo of the 

 fluid contains about 700 grammes of ammonium sulphate. 



In order to separate the larger part of this salt, the solution is 

 briskly boiled, evaporation being aided by keeping it continually 

 stirrea (preferably by an automatic stirrer). When sufficiently con- 

 centrated, the whole is exposed to as low a temperature as possible, 

 and the concentrated solution is separated, by decantation and 

 thorough draining, from the crystalline mass which has formed. 



The now yellow-coloured solution is mixed with one-fifth of its 

 volume of alcohol, which causes an abundant separation of crystals 

 of ammonium sulphate ; after their separation, the turbid liquid is 

 poured off, when it is observed to separate into two layers, a lighter 

 supernatant layer, which contains much alcohol with a large quantity 

 of peptone, and a heavier layer, which contains a large quantity of 

 ammonium sulphate in solution, but relatively little peptone. 



These two layers are separated from one another, as far as 

 possible by simple decantation, and then by employing a separating 

 funnel. The heavier solution, rich in ammonium sulphate, previously 

 referred to, is treated with successive quantities of alcohol ; each 

 addition by the latter causes the separation of additional quantities 

 of yellowish peptone and alcohol-holding supernatant liquid, which 

 floats on the surface of the aqueous solution of ammonium sulphate. 

 The latter on each addition of alcohol further furnishes deposits com- 

 posed of crystals of ammonium sulphate. 



The alcoholic solution, comparatively rich in peptones and poor 

 in ammonium sulphate, which results from all these operations, 

 having been placed in a stoppered bottle, is exposed to a very low 

 temperature, for at least twenty-four hours. The yellow alcoholic 

 solution may then be decanted from the thick and hard crystalline 

 crust of ammonium sulphate which has separated. 



It is now boiled, so as to drive off the whole of the alcohol, and 

 afterwards boiled with barium carbonate. The latter process serves 

 to decompose the ammonium sulphate yet present, barium sulphate 

 being precipitated and ammonia evolved. Ktihne recommends that 

 ammonia and ammonium carbonate should be added during the 

 process of decomposition with barium carbonate, and states that by 

 proceeding in this way he has succeeded in obtaining a solution of 

 peptone which contained neither sulphuric acid nor barium in solu- 

 tion. If this desirable result has been attained, the solution of 

 peptones is filtered ; it may then be further boiled until all ammonia 

 is expelled and is concentrated to almost syrupy consistence on 

 the water bath. The syrupy liquid is then poured into pure 



