NON-DISSOCIABLE INORGANIC RADICAL 169 



gelatin, prepared by the action of nitrous acid upon gelatin, 

 notwithstanding the absence of end NH2 groups, still retains the 

 power of binding CI' ions in solutions of hydrochloric acid. 



Oryng and Pauli (20) have shown that serum albumin, gelatin 

 and deaminized gelatin, dissolved in solutions of potassium chlo- 

 ride, bind a definite proportion of CI' ions, and this proportion 

 is greatly increased by the addition of acids (such as sulphuric 

 acid) to the solution. 



Confirmatory evidence is not lacking. Loevenhart (15) and 

 others * have found that rennet will not coagulate calcium casein- 

 ate unless a small amount of a dissociable salt of calcium is present. 

 The calcium bound by the casein itself is not available for this 

 purpose, but if a small quantity of acid be added then a pro- 

 portion of the calcium is freed from its combination with casein 

 and, if it forms a dissociable salt with the added acid, it is able 

 to bring about coagulation. 



W. A. Osborne (21) has shown that if calcium caseinate be 

 placed inside a dialysing tube which is then immersed in a very 

 dilute solution of mercuric chloride the mercury diffuses into the 

 tube and is there held in an undissociated form, since the con- 

 centration of mercury within the tube is found, after some time, 

 to considerably exceed that of the mercury in the outside fluid. 



Similarly, it has been shown by Moore, Roaf and Webster 

 (18) that if casein dissolved in dilute sodium hydroxide be placed 

 inside an osmometer of which the membrane is permeable to crys- 

 talloids but not to colloids and the concentration of NaOH be 

 rendered initially equal on both sides of the membrane, then 

 NaOH will move into the osmometer against the osmotic pressure 

 gradient and actually lead to a pronounced increase in the pres- 

 sure within the osmometer. It is evident, therefore, that not 

 only OH' but also Na+ ions must have been bound by the protein, 

 since otherwise no movement of Na+ across the membrane could 

 have occurred. 



* The statement of van Dam (6) that the extent of coagulation depends 

 upon the quantity of Ca hound by the casein is not irreconcilable with Loeven- 

 hart's results. As is well known, the calcium bound in casein as calcium 

 caseinate does not suffice to bring about coagulation. A dissociable salt of 

 calcium must also be present. That this salt may combine with the calcium 

 paracaseinate to form a double salt analogous to those described in the 

 previous chapters, is not at all unlikely. 



