viii THE GENERAL PHYSICAL PROPERTIES OF ALBUMINS 265 



will remain in ' solution ' as long as the H-ions, joined to the colloid, 

 enable its aggregates to maintain a definite charge. As the colloidal 

 particles become larger and larger, and the number of electrical charges 

 for a given volume of solution fewer and fewer, complete precipitation 

 will probably be induced at a time short of perfect neutralisation of 

 the charges, because of the specific gravity of the colloid-aggregates 

 overcoming the viscosity of the fluid." l 



When a colloid becomes iso-electric it ceases to be a colloid ; and 

 provided that the framework which is formed during the process of 

 rendering a colloid iso-electric is broken down mechanically, the newly 

 formed iso-electrical or non-ionised compound will fall to the bottom 

 of the vessel as an insoluble precipitate. 



Why the colloid does not unite in every case with the radical 

 having the stronger electro-affinity, why, for example, after the 

 addition of an acid the colloid unites with H, which has less electro- 

 affinity than K, while after the addition of an alkali it does not 

 unite with K but the OH', which latter has also less electro -affinity 

 than K, seemed, in 1902 to the author, "to be determined by the 

 fact that H and OH' are those very radicals which by their union 

 form water, and which therefore may have special chemical 

 affinities for the colloid, inasmuch as the latter owes its existence 

 to having been formed in water." Now the author is of the 

 opinion that colloids link on to H or OH 7 for the very reason that 

 these radicals have less electro-affinity, on the principle that a compound 

 becomes the more insoluble the greater the agreement is in the 

 amounts of the electro-affinities carried by the kat-ion and by the an-ion. 

 According to this view, silver has the same amount of + electro-affinity 

 as chlorine has - electro-affinity, and hence silver chloride is insoluble. 

 The same reasoning would apply to other insoluble salts, and seems to 

 be supported by the fact that colloids carrying a negative charge are 

 most readily precipitated by colloidal hydrates carrying a positive 

 charge. See later, p. 270, under Spring and Biltz. 



In this connection the precipitation of colloidal solutions by the 

 addition of ' neutral ' salts must be mentioned. Even if we assume 

 that the added neutral salt does not interfere in any chemical manner 

 with the colloid we are experimenting with, it is evident, if the author's 

 view is correct namely, that electro-affinities in equivalent intensities 

 but of opposite sign attached to two radicals lead to these two radicals 

 forming insoluble compounds that salts which are soluble and capable 

 of electrical dissociation must for this very reason be composed of ions 

 which differ from one another as regards their electro-affinities. If, 



1 Mann, Physiological Histology, p. 46. 



