420 Mr. W. B. Hardy. [Apr. 9r 



tion of 7*59 grammes globulin per litre, the transpiration times are in the 



ratio — 



Water 1 



MgS0 4 globulin 4'66 



HC1 „ 155 



NaOH „ 679 



In solutions of salt globulin, the globulin particles do not carry electricity ;: 

 " ionic " proteid is completely absent, therefore the higher viscosity of acid 

 and alkaline globulin solutions is connected with the presence of "ionic" 

 proteid, that is, of very large molecules carrying a charge. 



Since globulin acts much more strongly as an acid than as a base, there 

 will be in similar solutions of HC1 globulin and NaOH globulin a greater 

 concentration of " ionic " proteid in the latter. Here, again, increased concen- 

 tration of " ionic " proteid goes with increased viscosity. 



These conclusions agree with the observations of Keyher* on the viscosity 

 of solutions of soap, and of Sacklirj" on solutions of the proteid caseinogen. 

 It would, however, be rash to fix upon the simple proteid or soap ion as the 

 agent. The effect of dilution, and of varying proportions of acid or alkali, 

 make it possible that the high viscosity is due to the presence of the 

 molecular complexes, which carry a surface charge, and which I have called 

 " colloidal " ions, or pseudoions. Thus, further addition of small quantities of 

 ammonia, beyond the amount necessary to dissolve the globulin to a trans- 

 parent solution, decreases the viscosity. Ammonia is a very weak base, which, 

 in solution, has a specific molecular conductivity much less than that of its- 

 compound with globulin. One cannot, therefore, refer the diminished viscosity 

 to diminished ionisation of the ammonia-globulin compound, but the optical 

 properties of the solution show that slight excess of ammonia does diminish 

 the size of the particles of the globulin. It raises the " grade " of the 

 solution. 



A comparison of the different types of solution of globulin raises, in a 

 special way, the question of the meaning to be attached to the phrase 

 " colloidal solution." Mixtures of very diverse character have been classed 

 as colloidal, some because they form jellies, others because they are physically 

 heterogeneous, others because the osmotic pressure is exceedingly low, others,, 

 again, because the electric conductivity is abnormally low. Of these, perhaps,, 

 the only constant attribute is physical heterogeneity. Solutions which 

 present any of the other distinctive features of the colloidal state always- 

 contain particles which are large enough to scatter light. 



* ' Zeits. f. Physik. Chem./ vol. 2, p. 743, 1888. 

 + Ibid., vol. 41, p. 672, 1903. 



