2 COLLOID CHEMISTRY AND THE 



of that subject colloid chemistry. The relations of this 

 special branch of knowledge to the general chemistry of the 

 proteins is so definite that a discussion of the position is 

 desirable. 



An independent branch of science arises when a number of 

 observations are in strong contrast to previous records. The 

 differences must be so striking that investigators are spurred 

 on to an intensive study of the most glaring peculiarities, and 

 the contrast between the new and the old knowledge serves to 

 define sharply the bounds of the new discipline. As time goes 

 on and the new knowledge increases, previous discoveries, which 

 appeared to have little in common with it, are seen in a new 

 light. Consequently, there is, in the first place, a period of 

 detachment from the main stream of knowledge, followed by 

 a second phase of reunion. When the new development is rich 

 in observations and laws peculiar to itself, it will maintain a 

 distinctive position even after the period of coalescence has 

 begun, particularly when it contributes new methods of inquiry. 

 In this way colloid chemistry has achieved its autonomous 

 position. 



Although there were distinguished workers in the field before 

 him, Thomas Graham (1851) must be acclaimed as the father 

 of colloid chemistry. Not only was he the first to set forth the 

 most important properties of colloids, but he further emphasised 

 the fundamental distinction between colloids and crystalloids 

 a distinction as wide as that between an organised substance 

 and a lifeless mineral. Indeed, so vivid was this distinction to 

 Graham and his immediate successors in research that any 

 connection between the properties of crystalloids and colloids 

 remained far in the background. Such a connection is, however, 

 very plain in the considerations which formed the starting point 

 of Graham's work. For he submitted the following line of 

 thought : all substances show a greater or less difference in 

 the rate or ease with which they pass from the solid or liquid 

 state into the state of vapour ; in many cases these differences 

 are sufficiently pronounced to form the basis of a method of 

 separation in fractional distillation. The differences in the rate 

 of diffusion in a liquid are not less pronounced than in the rate 



