viii THE REMOVAL OF H AND OH' RADICALS 295 



3. A neutral pseudo-basic proteid, by addition of the acid H, 

 is converted into a real base, and the pseudo-acid colloid by the basic 

 OH 7 radical is changed into a real acid (the Author). 



4. The proteid forms with the H a kat-ion, or with the hydroxyl- 

 ion, an an-ion, the an-ion in the former case being the an-ion of the 

 acid which was added, while in the second case the kat-ion is the 

 kat-ion of the alkali we added (the Author). 



Whatever view we adopt, if we are dealing with a (colloid + H), 

 then, by the addition of the OH 7 group neutral water is formed, 

 H + OH 7 = H 2 0, and the charge on the proteid also disappears, 

 immaterial in what way it was induced. For reasons given on p. 264 

 the colloid then aggregates into larger masses, and is ultimately com- 

 pletely precipitated. 



The precipitation in this case depends therefore on the chemical 

 union between the hydroxyl- and the hydrogen-ions producing electri- 

 cally neutral water, and thereby diminishing or completely destroying 

 the electrical charges on the colloid. Another method of rendering 

 the hydrogen-ion inert is to convert it into the non-ionic state by 

 removal of the an-ion to which it was linked, as in the following case : 

 Given faintly acid solutions for example, an acid albumin coagu- 

 lation may be induced by the addition of neutral salts of the alkalies 

 or of alkaline earths, because this addition drives out the carbon 

 dioxide contained in the water and thereby renders the solution 

 less acid. The less acid the albumin solution is, to begin with, 

 the less neutral salt will be required for complete coagulation. 



Alkali-albumins in an alkaline solution are coagulated by the 

 addition of C0 2 , or other dilute acids ; by small quantities of alkaline 

 earths, probably because of the formation of insoluble hydrates ; 

 further, by dilution with water or dialysis against pure water ; and 

 lastly, by saturated solutions of sodium chloride or magnesium sul- 

 phate. All these reactions, with the exception of the last, which is 

 caused by salting-out, see p. 280, depend directly on the alkalinity or 

 the acidity of the proteid compound being interfered with. When 

 Starke states that the acidity of a dilute acid is diminished by neutral 

 salt, it must be remembered that this only holds good if the acid and 

 the salt have a common ion. Starke also observed that if the same 

 amount of alkali is added to two test-tubes, one of which contains pure 

 distilled water while the other contains an equal amount of pure sodium 

 chloride solution made up with the same distilled water, litmus-paper 

 is turned much bluer by the salt solution. The explanation he offered 

 was that alkalies in the presence of neutral salts dissociate to a greater 

 extent, and therefore give a more pronounced alkaline reaction. This 



