706 PROTEIDS. [App. 



As special tests of acid-albumin may be given : 1. Partial coagu- 

 lation of its solution in lime-water on boiling. 2. Further precipitation 

 of the same solution sifter boiling, on the addition of calcic chloride, 

 magnesic sulphate, or sodic chloride. 



Dissolved in very dilute hydrochloric acid, acid-albumin (syntonin) 

 -prepared from muscle possesses a specific laevo -rotatory power of -72 for 

 yellow light, this being independent of the concentration 1 . On heating 

 the solution in a closed vessel in a water-bath, the rotatory power rises 

 to -84-8. 



The body known as parapeptone which makes its appearance during 

 the peptic digestion of proteids is closely allied to the substances just 

 described. (See p. 243). 



2. Alkali-albumin. 



If serum- or egg- albumin or washed muscle be treated with dilute 

 alkali instead of with dilute acid, the proteid undergoes a change quite 

 similar to that which was brought about by the acid. The alkaline 

 solution, when the change has become complete, is no longer coagulated 

 by heat, the proteid is wholly precipitated on neutralisation, and the 

 precipitate, insoluble in water and in neutral sodic chloride solutions, 

 is readily soluble in dilute acids or alkalis. Indeed in a general way 

 it may be said that acid-albumin and alkali-albumin are nothing more 

 than solutions of the same substance in dilute acids and alkalis 

 respectively. When the precipitate obtained by the neutralisation of 

 a solution of acid-albumin in dilute acid is dissolved in a dilute alkali, 

 it may be considered to become alkali- albumin ; and conversely when 

 the precipitate obtained from an alkali-albumin solution is dissolved in 

 dilute acid, it may be regarded as acid-albumin. 



It is stated 2 as a characteristic reaction of this modified or derived 

 albumin that it is not precipitated when its alkaline solutions are 

 neutralised in the presence of alkaline phosphates; solutions of acid- 

 albumin on the contrary are said to be precipitated on neutralisation in 

 the presence of alkaline phosphates, and this difference is considered 

 to be a distinguishing feature of the two proteids. But doubt has been 

 cast on this statement *. 



Alkali-albumin may be prepared by the action not only of dilute 

 alkalis but also of strong caustic alkalis on native albumins as well as 

 on coagulated albumin and other proteids. The jelly produced by the 

 action of caustic potash on white of egg, spoken of in Class I. 1, is 

 alkali-albumin ; the similar jelly produced by strong acetic acid is acid- 



1 Hoppe-Seyler, Hdb. Phys. Path. Chem. Anal. Ed. iv. (1875), S. 246. 

 3 Hoppe-Seyler, loc. cit. S. 245. 

 3 Soyka. Pfltiger's Arch. Bd. xn. (1876), S. 347. 



