io CONDITIONS OF STABILITY 



CHAPTER II 

 CONDITIONS OF STABILITY IN PROTEIN SOLUTIONS 



THE definition of a colloid system as a dispersion within 

 certain limits of subdivision is satisfactory in emphasising a 

 general property ; it does not, however, suffice to define special 

 cases when certain hypotheses become necessary to complete 

 the description. These serve to subdivide colloids into broad 

 classes. Thus Wo. Ostwald has devised a' classification based 

 on the state of aggregation of the disperse phase. Colloids 

 with solid disperse phase are suspensoids, those with liquid 

 particles emulsoids. If the dispersion in such systems is 

 reduced so that the disperse phase coalesces into macroscopic 

 masses, the suspensoids give solid coagula, which settle out of 

 the liquid. The emulsoid particles, in contrast, flow together 

 into drops, which frequently unite to form a separate liquid 

 layer. 



" If a io per cent, gelatin solution is precipitated at 30 by addition 

 of a neutral salt (e.g., sodium sulphate) and allowed to stand for some 

 hours at the same temperature, the gelatin is found in both layers, the 

 upper more liquid one containing but little gelatin, the lower layer being 

 rich in gelatin (Wo. Pauli and P. Rona*). A similar effect has been 

 observed and further studied by K. Spiro f when casein is coagulated by 

 heat." 



The classification of colloids from another point of view is 

 important in characterising the physical properties of the pro- 

 teins. Both in the case of typical solutions and in that of 

 colloidal solutions, a greater or less combination between the 

 particles and the solvent or continuous phase has been shown 

 to exist. Crystalloids are said to be hydrated^or, in general, 

 solvated) in solution when water is attached to the dissolved 



* Beitr. z. chem. Physiol. u. Path., 1902, 2, i. 

 t Beitr. z. chem. Physiol. u. Path., 1904, 4, 300, 



