PRECIPITATION AND COAGULATION 133 



mass of salt, provided this is sufficient to enter into combination 

 with the protein {vide equation iii), i.e., it is possible to bring 

 about precipitation by mere dilution, the relative masses of 

 protein and salt being unaltered. 



(v) The precipitation of proteins by salts occurs more readily 

 in acid than in alkaline solutions {vide equation iii). 



(vi) The observation of Bonamartini and Lombardi (6)* that 

 egg-albumin in neutral solution combines with both the basic 

 and the acid radicals of copper sulphate in equivalent propor- 

 tions to form an insoluble compound but that m alkaline solu- 

 tion it combines with excess of copper to form a soluble compound 

 {vide equation iv). In alkaline solution hydrolytic dissociation 

 of the complex salt is pushed back in accordance with the fol- 

 lowing equations. 



CUSO4 + 2K0H -^ K2SO4 + Cu(0H)2 



H2N.R.CO.N.R.COOH H2N.R.CO.N.R.COOH 



/' \H / ' \ 



Cu(0H)2+ Cu( S04)„ -> CuC SO ;Cu -F2H20 



\ I / H \ I X 



H2N.R.CO.N.R.COOH H2N.R.CO.N.R.COOH 



(vii) The observation of Osborne (Cf. Chap. V) that edestin 

 crystallized from concentrated salt-solutions will decompose the 

 salt, binding the base, is probably attributable to the reaction: 



H 

 I 

 HaN.R.CONa.N.R.COOH + NaCl 

 I 



CI Na 



I 



= H2N.R.C0NaN.R.C00H + HCl 



I 



CI 



the complex salt being in this case insoluble. 



(viii) The observation of Pauli that precipitation of a protein 

 by salts when it is non-ionic is impossible. For, when the pro- 

 tein is not ionized the nitrogen is bound up in undissociated 

 — COH.N— groups and is not attached to H+ and OH' groups 

 replaceable by the ions of the salt. 



* The egg-albumin employed by these observers is not ash free; it must, 

 therefore, according to Pauli have been ionic. 



