i8 PHYSICS OF STREAMING 



solutions (one gram molecule per litre) of inorganic salts varies from ii to 

 1-3, and of organic salts from 1-3 to 1-8. In the case of normal solutions 

 of NH 4 C1, KC1, and KNO 3 , the ratio is 0-97, and in that of KI, 0-91 J , solu- 

 tions of these substances having a less viscosity than pure water. The 

 decrease is slight, but it increases with the concentration : thus in the case 



o * 



of a 7 per cent, solution of KNO 3 , 77 = 0-0169, in that of a 14 per cent, 

 solution, T] = 0-0155. Hence the viscosity of the cell-sap under ordinary cir- 

 cumstances probably lies between o-oi and 0-02 at 20 C. In cells loaded 

 with sugar (beet-root, onions, &c.) the viscosity may rise to from 0-03 to 006 

 at 20 C.j and the retarding or preventive effect of the cell-sap upon stream- 

 ing or upon any tendency to streaming would be proportionately increased. 

 From a purely physical point of view protoplasm is to be regarded 

 as consisting mainly of a colloidal albumin containing large and varying 

 percentages of water, the latter having a very pronounced influence upon 

 its viscosity. Hence it is of importance to know the values for colloidal 

 solutions such as ordinary egg- and serum-albumin. 



SECTION 7. Viscosity of Albuminous Solutions. 



Instead of attempting any absolute measurements, the easier method 

 was adopted of comparing the rates of flow of equal volumes of egg- 

 albumin, and of liquids of known viscosity through a capillary tube under 

 the same pressure and in the same direction. The albumin was obtained 

 from fresh eggs, snipped in all directions with sharp scissors, and then 

 filtered under pressure through linen in order to remove its ropy character. 

 The first samples used contained from 89-4 per cent, to 89-9 per cent, of 

 water, their density being 1-043. 



In a particular experiment 2 with 99 per cent, glycerine of density 

 i 3612 (at 19-3 C.) the time of flow was 43 min. 20 sees, at i8-5C., and of 

 the same volume of egg-albumin 120 sees, at 18-5 C. 



Now r/ : r/' : : td : t'd', where TJ and r/', are the viscosities of the albumin 

 and glycerine respectively, t and t' their times of flow, and d and d' their 

 densities. Substituting these values and the known viscosity of glycerine 

 at this temperature, TJ = 0-381. 



When, as in this case, the difference of velocity is very great, various 

 errors are introduced. Thus the resistance instead of increasing in direct 

 proportion to the velocity, may increase as a power of the speed rising to 

 as much as 1-8, so that in comparison with the more viscous glycerine, the 

 albumin appears to have a higher viscosity than is really the case. Thus 



1 Landolt and Bornstein, Phys. Chem., Tabellen, p. 293. 



8 In all cases the time of out-flow was taken, and the lower end of the capillary kept immersed 

 beneath the liquid, so as to avoid the formation of drops and consequent errors due to their surface- 

 tension retarding the out-flow. (See Fig. 4, p. 21.) 



