vin THE GENERAL PHYSICAL PROPERTIES OF ALBUMINS 259 



it does not mean that a fundamentally new state of matter is 

 reached whenever we pass from invisible to visible particles. There 

 is no transition between electrolytes and colloids, as far as Tyndall's 

 test is concerned. 



Picton in 1892 1 divided arsenic-sulphide, As 2 S 3 , solutions, accord- 

 ing to their physical state, into four classes, which he called a, ft, y, 

 and 8. The a-solution is termed a pseudo-solution, because under a 

 magnification of 1000 diameters the fluid is seen to contain crowds of 

 minute suspended particles in rapid Brownian movement. The 

 /3-solution, forming the transition to the y-variety, is composed of 

 particles so small as to be microscopically invisible. The y-solution 

 differs from the a and /3 ones in diffusing and exerting osmotic 

 pressure, but it cannot be filtered through a porcelain filter without 

 the solid separating out, while the S-solution contains sulphide particles 

 of so small a size as to pass readily through the filter. 



Now Picton's a-solution is comparable to what is ordinarily called 

 a colloid, and his S-solution to what is usually termed an electrolyte. 

 The difference between a colloid and an electrolyte is, therefore, in 

 one respect, purely one of size, or a quantitative one ; the difference 

 becomes qualitative only in respect to the unit of electrical charge 

 carried by each individual particle. 



OTHER PHENOMENA. If polarisation does not allow us to dis- 

 tinguish between electrolytes and colloids, then all the other character- 

 istics mentioned on p. 257, under Nos. 2 to 9, point directly to colloids 

 being electrolytes as long as they are in ' solution.' 



This view, first advanced in 1902 by the author in his Physiological 

 Histology, p. 45, accounts in general for the movement of colloids ' in 

 solution,' when they are subjected to an electrical current, and also 

 explains the special case of the behaviour of heat-coagulated albumin. 

 Hardy's observation that iso-electric heat-coagulated albumin moves 

 neither towards the anode nor towards the kathode, while after the 

 addition of a trace of acid it moves towards the kathode, and after 

 the addition of an alkali towards the anode, the author explained thus: 

 " As the proteid acquires the charge of the positive hydrogen-ion of 

 acids, and the negative charge of the hydroxyl-ions of alkalies, we may 

 assume the hydrogen- or hydroxyl-ions to unite with aggregates of 

 proteid-molecules, and thus to form new ions consisting of the 

 (colloid + H) or (colloid + OH)'. The anion of the acid which was 

 added (for example, the negative chlorine- or acet-ions) or the kation 

 of the alkali (for example, the positive sodium-ions) become the com- 

 panion-ions to the (colloid + H) or the (colloid + OH)'-ions." 



1 Harold Picton, Jawrn. Cham. Soc. 61. 137 (1892). 



