VISCOSITY 325 



and ionic motion. Thus a netlike structure, such as a tennis net, 

 will offer no hindrance to the passage through it of a quickly- 

 moving body which is smaller than its meshes, other than that 

 which is due to the fact that the material which composes the net 

 occupies a small fraction of the area which the body must traverse, 

 but to any force which involves deformation of the structure, for 

 instance, a force which seeks to drag it through a small tube, it will 

 offer a very considerable resistance. On the other hand the 

 resistance which is offered to a small moving body by a viscous 

 liquid (viscous, that is, in the ordinary sense) is accurately meas- 

 ured by the resistance which the liquid offers to passage through 

 a tube. Now the direct methods which we employ to measure 

 the viscosity of fluids are all such (rotation of a relatively large 

 body within the fluid; passage of the liquid through a capillary 

 tube, etc.) as would involve the deformation of any molecular 

 structure within the fluid. Our direct methods of estimating 

 viscosity do not enable us to distinguish between that type of 

 viscosity which is attributable to a structure within the fluid and 

 the other type of viscosity which we may term "true" internal 

 friction. The indirect measurement which the conductivity esti- 

 mations afford, however, only reveals the latter type of viscosity 

 and, as we have seen, when we employ this method of estimation 

 the presence of protein is found to leave the viscosity of the solvent 

 unaltered.* 



If we admit, however, that the viscosity of protein solutions is 

 due to a molecular net-structure within them, then we are forced 

 to a conclusion which, in the light of our present inadequate 

 knowledge of the mechanics of ionization, appears very curious. 

 We have seen (Cf. above) that the viscosity of protein solutions 

 must be attributable, primarily, to the protein ions which they 

 contain. We are led to conclude, therefore, that the net-structure 



* Save to the degree involved by the fact that the material composing the 

 net-structure occupies a certain proportion of the cross-area of the conducting 

 field. As we have seen above, the results of Dumanski show that if allowance 

 be made for this diminution in cross-area the conductivities of solutions of 

 electrolytes in gelatin jelhes are nearly identical with those of equally concen- 

 trated solutions in water. The slight deviations which Dumanski observed 

 are probably attributable to the fact that the calculation of this diminution in 

 area involved the specific gravity of the gelatin in its dissolved condition, and 

 this is not necessarily the same as that of unhydrated gelatin, i.e., gelatin in 

 its undissolved condition. 



