138 CHARACTERS OF PEPTONES. [BOOK II. 



Distinguishing Characters of Peptones. 



Physical However different the proteids which are employed 



in their preparation, peptones all possess, essentially, 

 the same physical and chemical properties. 



When freshly precipitated and moist, pure peptones are white, 

 resembling freshly precipitated casein ; if the yet moist mass be 

 heated to between 80 and 90 C., it has a tendency to melt into a 

 fat-like mass which solidifies on cooling (Adamkiewicz and Hoff- 

 mann). Dried peptones appear as brittle, yellowish-white, solids, 

 soluble in any proportion in cold or hot water, and from their great 

 affinity for water, highly hygroscopic. They are insoluble in ab- 

 solute alcohol, in ether, chloroform, and hydrocarbons : they dissolve 

 in aqueous alcohol, according to the amount of water which it con- 

 tains. The aqueous solutions of peptones have a neutral reaction, 

 rotate the plane of polarization to the left, and possess a higher 

 diffusive power than other soluble proteids ; to this character, atten- 

 tion will again be directed. 



Non-precipi- When solutions of peptones are pure they are not 



tation by heat precipitated when boiled, nor on the addition of any 

 and nitric acid. m i ner al acid. Adamkiewicz has asserted that this 

 statement is not true of very strong solutions of peptones, which, he 

 says, are precipitated by heat and mineral acids. The statement has 

 not, however, been confirmed by the very careful examination by 

 Herth of albumin peptone, nor does it agree with the author's 

 observations. It doubtless rests upon the fact that Adamkiewicz 

 worked with impure peptones. 



Non-precipi- ^ ne most characteristic difference, according to 

 tation by acetic authors, between solutions of peptones and all other 

 acid and ferro- proteid bodies, is found in the difference of behaviour 

 cyanide of { o acetic acid and potassium ferrocyanide. Every pro- 

 teid body in solution, with the single exception of 

 peptones, is precipitated if acetic acid be first added and then a 

 solution of potassium ferrocyanide. 



It must not be supposed however that even the peptones are 

 wholly unacted upon by these reagents, for, however carefully they 

 may have been purified, it is found that the addition of acetic acid 

 and potassium ferrocyanide, though at first without effect in the 

 solution, which remains perfectly clear, ultimately causes some opa- 

 lescence (Kiihne and Chittenden); this is, however, very different 

 from the abundant precipitation occasioned by the same reagents 

 with other proteids. 



Neutral and basic lead acetates only produce turbidity when 

 added to solutions of peptones. Solution of copper sulphate (5 p.c.) 

 does not affect a solution of ampho-peptones. Similarly, according 

 to Kiihne, solutions of platinum chloride, chromic acid, and ferric 

 chloride are without action upon them. 



