340 PHYSICAL PROPERTIES 



dissolved through the membrane so that the space within the 

 latter may become nearly empty. It is probable that these phe- 

 nomena depend rather upon the extreme affinity of this colloid for 

 water than upon ordinary osmotic forces. 



C. J. Martin (68) and W. M. Bayliss (5) find that the os- 

 motic pressures of egg-albumin and of haemoglobin solutions vary 

 directly with the absolute temperature, thus obeying the law of 

 Gay-Lussac. 



7. The Nature of Protein Solutions. — The view has been held 

 by many investigators that the proteins, and colloids generally, do 

 not enter into true solution, forming molecularly dispersed systems 

 which obey the law of Avogadro, but are to be regarded, on the 

 contrary, as forming stable suspensions when they appear to pass 

 into solution in water; a view which reaches its most extreme 

 expression in the statement of Duclaux (26) that "Les Colloids 

 doivent etre consideres comme etant, dans I'eau, d'une insolubilite 

 absolue." Others, arguing* from the a priori assumption that 

 "solutions" of colloids are necessarily, in reality, suspensions, have 

 objected to the application of theoretical principles to them which 

 involve the law of Avogadro (such as the mass-law, etc.). It is 

 obvious that this is a reversion of the customary procedure of 

 science; the applicability of a law is in the first place a question in 

 itself, independent of any other generalizations, and, in the second 

 place, the applicability of a law involving Avogadro's law may in 

 itself be regarded as presumptive evidence that the law of Avo- 

 gadro applies as well. 



From what has been said above, it is evident that under certain 

 conditions, particularly in the form of their salts, the proteins 

 diffuse in water and exert a definite osmotic pressure. Hence 

 Avogadro's rule must hold good, although the time required for 

 the protein molecules to distribute themselves uniformly through- 

 out any given volume of fluid may conceivably, in certain instances, 

 be very great. 



Apart altogether from direct observation, however, the posses- 

 sion of a definite osmotic pressure by proteins and certain other 

 colloids in solutions is directly deducible from the fact that chemi- 

 cal reactions which involve them attain definite equilibria (101). 

 The work which is performed in the transformation of a molecule 

 of substance is the sum of two factors, the one the chemical work 



* For example, W. Nernst (75). 



