VISCOSITY 327 



as more of the salt is added, but the curve displaying the influence 

 of the concentration of the salt upon the viscosity of the solution 

 exhibits very marked maxima and minima. Now Ostwald has 

 found that the influence of added salts upon the swelling of gelatin 

 plates in water (Cf. Chap. XII) is of a similar character to their 

 influence upon the viscosity of gelatin solutions; that the degree 

 of swelling runs closely parallel with the diminution in the viscosity 

 of solutions, as determined by von Schroeder, since the concen- 

 trations of salts at which maxima of swelling occur are nearly identi- 

 cal with those at which minima in the viscosity of solutions are 

 observed. From this Ostwald argues that the passage of gelatin 

 into solution does not destroy the structure of the gel but that this 

 structure persists in solution. 



Sutherland (119) in developing the theories to which I have 

 referred above, has also expressed the opinion that protein solu- 

 tions possess a structure.* 



Of great interest in this connection is the observation which a 

 number of investigators have made (110) (59) (34) (109) (33) that 

 the viscosities of gelatin solutions, insufficiently concentrated to 

 gelatinize, change somewhat on standing. Garrett has also 

 observed (33) that the logarithmic decrement of a disc oscillating 

 in gelatin or albumin solutions is not a constant, as it is in water 

 or other homogeneous fluids, but, on the contrary, increases as a 

 linear function of the time. This was traced to adhesion between 

 the disc and the protein ; if the disc was taken out of the fluid and 

 washed the initial value of the decrement was always the same. 

 This is obviously to be explained, on the basis of the above 

 hypothesis, by the adhesion of portions of the net-structure to 

 the oscillating disc. Garrett has further observed that very 

 slight mechanical disturbance of a gelatin solution produces con- 

 siderable alteration in the magnitude of the oscillation-decrement. 



Preliminary heating diminishes the viscosity of gelatin solutions 

 and the magnitude of the effect is a function of the time of expo- 

 sure to the higher temperature (110) (33). Garrett attributes this 

 phenomenon to a partial destruction by heating of a structure 

 within the fluid. Ostwald (79) has found that preliminary- 

 heating of gelatin increases the rapidity with which it swells in 

 water. He also interprets this by supposing that the structure of 



* Cf. also C. O. Weber (128). 



