344 PHYSICAL PROPERTIES 



a second estimate, regarding the oxygen as hydroxyl oxygen 

 (difference due to one atom of hydroxyl oxygen = 7.8), yields the 

 molecular volume 17,960. The volume, estimated in this way, 

 therefore, lies between 18,000 and 19,000. The absolute volume of 



i i -n +u 't r u 18,000 , 19,000 , 



the molecule will therefore he between - and or about 



o.o o.o 



3400 times that of a hydrogen molecule, and about 523 times that 

 of a molecule of carbon dioxide. The diameter of the molecule 

 will, therefore, be approximately v^523 = about 8 times that of a 

 molecule of carbon dioxide. Now the diameter of a molecule of 

 C02 is, according to Nernst (74), 0.3 w, hence that of a molecule 

 of casein must be about 2.4 /*/*, or about one-half the diameter of 

 the smallest particle which will scatter transmitted light. Ad- 

 mitting the great uncertainty which, in our present state of 

 incomplete knowledge, attaches to such estimations as these, we 

 must yet admit that it is improbable that the opalescence of solu- 

 tions of proteins such as casein is directly attributable to the 

 protein molecules themselves; and it appears the more improbable 

 when we recollect that in pronouncedly opalescent solutions casein 

 salts, and many other protein salts are, as we have seen (Chaps. 

 VIII-X), quite extensively ionized, that is, split up into particles 

 which occupy, themselves, a fraction of the volume computed 

 above. When we recollect that the non-filterable character of 

 many proteins in solution (Cf. Chap. VII, section 6) and the vis- 

 cosity of protein solutions (Cf . the earlier part of this chapter) are 

 alike attributable to ionic protein, the suggestion offers itself that 

 the opalescence of protein solutions (as distinguished from that of 

 suspensions of partially coagulated protein) may possibly be 

 attributable to the peculiar characteristics of ionic protein. It is 

 possible that the non-filterable character of ionic protein and its 

 power of scattering transmitted light are alike due to a bulky 

 water-complex, which is associated with each of the protein ions 

 (Cf. Chap. VI, section 6 and Chap. VII, section 6). In support of 

 this view may be mentioned the remarkable fact that the addition 

 of alcohol or of acetone, in quantities insufficient to initiate coagu- 

 lation, to solutions of the caseinates leads to a very decided de- 

 crease in their opalescence. On the other hand, it is possible that 

 the net-like structure which we have seen reason to believe that 

 protein ions form in solution (section 1, this chapter) is account- 

 able, not only for the viscosity of solutions of ionic protein, but 



