276 CHEMISTRY OF THE PROTEIDS CHAP. 



shows that with egg-albumin only the lines of maximum shear (the 

 wrinkles) persist as coagulated proteid, while in the intervals between 

 these lines the coating particles retain their solubility. 



Mechanically coagulated proteid thus obtained bears a strong 

 general resemblance to fibrin, and, like fibrin, can be ' coagulated ' still 

 further by heat. Ramsden maintains that mechanical surface coagula 

 must be regarded as consisting of chemically unaltered colloid 

 particles which by mere mechanical inpaction have been driven into 

 closer physical union. This union is held by Ramsden to be physical 

 rather than chemical, in the same sense that the union of silicic acid 

 particles must be regarded as physical, when a colloid solution of silica 

 is coagLilated by the addition of an electrolyte. 1 In all such cases 

 there is no limit to the size of the molecule which can be built up, 

 and the chemical term ' polymerisation ' is undesirable, since it would 

 then be necessary to regard the continuous solid framework of a gel 

 as composing one large molecule. 



Ramsden therefore advances the view that some forms of 

 coagulation, including mechanical surface coagulation, and fibrin 

 formation (see p. 382), are essentially physical processes, due entirely 

 to the close physical union of previously distinct colloid particles and 

 involving no demonstrable chemical change. 



Incidentally may be mentioned that all bubble-forming liquids have 

 been shown by Ramsden to yield mechanical surface aggregates, and 

 conversely that the power of forming thin films, bubbles, or froth, in 

 any limpid liquid, is due to the presence of solid surface coatings. 

 Similarly the permanence of any good emulsion is due to the forma- 

 tion of a coating of solid particles, or veritable haptogen-membrane, 

 at the interfaces between the emulsified globules and the menstruum 

 in which they are suspended. 



The haptogen-membrane which forms when milk is boiled is fully 

 discussed by Jamison and Hertz. 2 



3. Coagulation due to Alterations in the Electrical Tension 

 between the Colloid and its Solvent. 



An electrolyte in dissociating into its ions always gives rise to an 

 amount of positive electricity which equals the amount of negative 

 electricity, and the electrical charges are carried by the ions. Each 

 kind of ion travels,~iurthep, with its own velocity, the two fastest ions 

 being the acid hydrogen- and the alkaline hydroxyl-ions. 



If now, for example, hydrochloric acid is poured into water, the 



1 The author does not hold this view ; see pp. 268-271. 

 2 R. Jamison and A. F. Hertz, Journ. of PhysioL 27. 26 (1901). 



